Elly Deacon Smith and Kirk Rushby from Arbor Architects explain why they consider the embodied carbon of their projects, how they do it and how it is balanced with competing factors.
Interview with Elly Deacon Smith and Kirk Rushby
Elly Deacon Smith is the Founding Director of Arbor Architects with nearly 25 years of experience. She began her career in Bristol at White Design, working on straw and timber projects that emphasised both embodied and operational carbon long before it became mainstream. After moving back to Herefordshire, she joined Architype, deepening her expertise in Passivhaus construction and building physics, before co‑founding Arbor Architects, which she now leads.
Kirk Rushby is an Associate at Arbor Architects with roughly 20 years in the field, fifteen of which were spent at Architype. His background mirrors Elly’s focus on sustainable, low‑energy design and bio‑based materials. He’s also built his own Passivhaus home.
Focusing only on the energy a building uses in operation misses a large portion of its climate impact. Embodied carbon covers emissions from material extraction, manufacture, transport, construction and demolition. Even a Passivhaus can carry a substantial carbon debt if high‑impact materials are used. Measuring both sides lets designers keep total lifetime emissions within targets like the RIBA 2030 benchmark.
“We’re aware that operational carbon is regulated, but embodied carbon is a bigger blind spot,” Elly notes.
Make sure your design team is carbon literate
Elly taught a master’s course at the Welsh School of Architecture. A key aspect she encouraged was to “think in carbon” for every decision. This habit makes it easier to spot high‑impact choices later, because the designer already asks, “What is the carbon cost of this material?” Kirk agrees that years of practice have turned this questioning into second nature. Early education therefore lays the groundwork for systematic carbon reduction and intuitive decisions.
Use specialist tools to quantify embodied carbon
Arbor initially hired an external consultant to run assessments in PH Ribbon, which can use a certain amount of information from the existing PHPP model. The consultant just required quantities for elements like walls, floors and roofs, enabling calculation of kilograms of CO₂ per square metre. More recently Kirk is using a tool from Studio Bark, whose emerging calculator pulls volumes directly from Revit models, delivering near‑instant feedback.
“We’re really keen to be able to model in‑house, and to be able to make decisions quite quickly,” Elly explains.
Tin Barn
Take advantage of real‑world case studies
Arbor’s retrofitted Tin Barn (certified to the EnerPHit standard) achieved about 347 kg CO₂ / m², comfortably below the RIBA 2030 target. By contrast, a newly built garden‑room annex with timber framing and zinc cladding recorded just over 600 kg CO₂ / m². Interestingly, adding a photovoltaic array increased the figure by roughly 100 kg CO₂ / m². Elly says that this is another good reason to take a fabric first approach so that you keep your energy needs to a minimum.
Cwm Barn
Test assumptions: zinc cladding may not increase carbon dramatically
Swapping timber cladding for zinc on the Cwm Barn garden‑room added only a modest amount of embodied carbon, perhaps contrary to expectations. Elly attributes this to the relatively small surface area and the fact that the underlying timber structure already contributed most of the carbon.
“One of the surprises was that the decision to clad the garden room in zinc didn’t have as big an impact as we thought,” Elly comments.
So the lesson is to evaluate material impact in context rather than doing it intuitively.
Quick checks, early in the design process, make it possible to consider embodied carbon for every project
Waiting weeks for external consultants slows down design decisions and is not practical in the long run. So using a simpler embodied carbon tool like the one from Studio Bark means the whole process becomes easier, different options can be evaluated and it can be integrated into the standard workflow.
Using bio‑based materials normally leads to a good carbon outcome
As a general rule at Arbor they like to build with timber. This stores carbon from the tree’s growth, giving it a lower embodied carbon compared to other methods of construction.
Recognise foundations and substructure as the biggest carbon hotspot
Concrete foundations are inherently carbon‑intensive and often difficult to get away from. However, you can reduce volumes with good design or use low‑carbon mixes. Sometimes screw piles can be a way to avoid concrete altogether but these will normally be made of steel which again has a high embodied carbon. That said, they can be removed and reused at the end of the life cycle.
Balance cost, client expectations and carbon goals early on
High‑performance homes and Passivhaus certification typically increase material quantities and costs a little. Arbor addresses this by being transparent with clients from the outset about trade‑offs between carbon performance and budget. Early budgeting conversations help align expectations, and designers explore “more with less” tactics—optimising layout, trimming unnecessary floor area, and selecting durable, low‑maintenance finishes that lower lifecycle costs. Kirk stresses that “you can get more out of less” with the right mentality.
Good decision-making considers many factors
Embodied carbon is just one aspect of a sustainable home. Arbor evaluates each material for moisture handling, indoor air quality contribution, longevity and visual ageing.
Designer experience and instinct are still important
For design teams that aren’t yet modelling embodied carbon, logical decisions can often lead to low carbon outcomes: prioritise low‑impact substructures, favour timber over masonry where feasible, reuse on‑site materials, and keep use of steel to a minimum.
Anticipate a future where measurement is seamless and data is shared
Whereas many design teams are familiar with operational carbon, the future could see quick‑feedback calculators embedded in standard workflows and a shared database of embodied‑carbon benchmarks for common building typologies. More data will enable designers to make confident, low‑carbon decisions early in the design process, accelerating the transition to a net‑zero built environment.
Marion Baeli, author of “Residential Retrofit,” offers hands-on experience of designing and retrofitting high performance homes. As well as drawing on her personal retrofit she shares the lessons learnt from revisiting properties that took part in the Retrofit for the Future competition over a decade ago.
Interview with Marion Baeli
Marion Baeli is Principal, Sustainability Transformation at 10 Design and author of “Residential Retrofit,” covering the evolution of retrofitting over the past decade. Originally a French architect, Marion came to the UK in 2002 and later took a master’s degree in sustainable architecture and design. This brought a fundamental shift in her approach so that she now embraces the Passivhaus methodology, and considers all aspects of embodied carbon and material circularity in her work.
She was fortunate to be part of the Retrofit for the Future competition and has been able to revisit several of the properties, ten years later to assess their performance. She also draws on the experience of her personal retrofit project to highlight the differences between good and bad retrofits.
Retrofit needs a holistic, system‑level approach
Marion stresses that many retrofit failures stem from treating the building as a collection of isolated fixes. She points out that focusing solely on insulation, without addressing moisture control, ventilation, airtightness, and thermal bridges, inevitably creates new problems. A coordinated design that balances all performance factors is essential for long‑term durability. This mindset is now embedded in standards such as PAS 2035, which require a comprehensive retrofit plan before work begins.
“You can’t really do a retrofit by looking at just one thing… you need a holistic approach.”
Start with thorough planning and expert co-ordination
For Marion the most reliable retrofits begin with careful upfront planning, bringing together architects, engineers, contractors, and a retrofit coordinator to ensure that each intervention is contributing to the overall performance target. Marion recounts that the original “Retrofit for the Future” case studies succeeded because the teams invested heavily in design time, avoiding costly re‑work later. Skipping this step often leads to unintended consequences and poor performance.
Long‑term performance holds up when quality is built in
When revisiting a number of the original case studies that featured in the book and carrying out building performance evaluation, Marion reports that airtightness, insulation integrity, and thermal bridge mitigation have largely remained intact. No major failures such as tape peeling or board collapse were observed, confirming that a well‑executed retrofit can be long-lasting. The key takeaway is that investing time and expertise at the start pays dividends in sustained performance and lower operating costs.
Watch our in-depth video case study of the Kinver retrofit in The Hub.
Regular maintenance of the building fabric is essential
Even the best‑designed retrofit can be undermined by neglected maintenance (which is obviously nothing to do with retrofit). Marion cites a case where a leaky gutter caused brickwork to spoil and moss growth which could have threatened the structural longevity. Simple upkeep, cleaning gutters, repairing cracks, and checking flashing helps preserve the gains achieved through retrofit.
Window and door seals degrade over time
One common observation of the post occupancy evaluation was that gaskets around windows and doors have begun to lose elasticity, potentially starting to compromise airtightness. Although these can’t simply be replaced at the moment Marion believes we should all be raising this concern with our window manufacturers. She explains that on bigger projects and social housing they develop relationships with these suppliers and so units might be removed, repaired and replaced. This circular approach is needed for one-off homes too.
Financing retrofit needs to look beyond ROI
Marion argues that retrofit is not about return on investment. She likens it to buying and maintaining cars; you don’t expect a return on your investment when you buy a car and you maintain your car to ensure its safety and longevity. In many cases, the key benefits of retrofit are reduced energy bills, improved comfort and health, along with future‑proofing against climate change. Creative financing, phased implementation, and leveraging grants can make the upfront cost manageable.
Marion bought a mid terrace home with a plan to retrofit it
The plan and timelime of the step-by-step retrofit
Step‑by‑step retrofitting can be a good way to spread out the costs
Rather than tackling the whole house at once, Marion describes the phased strategy that she adopted. This involved making changes to the internal layout first as well as installing ground floor insulation and the ducting for the MVHR. Later she was able to address the external façade and windows, making sure that the house maintained its integrity with the other 1960’s houses on the estate. This allowed her to spread the costs over several years, while still moving into the house after the first phase. Planning each stage to dovetail with the next ensures that interim works do not compromise later performance targets.
“We’ve spent a lot of time planning the ductwork route – that’s the most difficult part of a retrofit.”
Significant construction work is better in one hit
Marion contrasts two approaches to construction disruption; to fully vacate the property for intensive works versus a staged, live‑in alternative. Her own project required a temporary relocation for six months, but she notes that many retrofits can be completed incrementally, allowing occupants to remain on site, perhaps moving around the house as the work is carried out. Choosing the right strategy depends on the building’s condition, the scope of work, and your personal tolerance for inconvenience!
A retrofit is often the time to look for other opportunities to make the building better
While carrying out the internal work, Marion added a light well to bring natural daylight into the core of the house, reducing reliance on artificial lighting. They also created bespoke timber storage units in the entrance hall and living area. In the summer months they are ready for a heatwave and have a pop-up fabric that they can stretch across the windows. Though simple DIY, this method effectively cuts solar gains, keeping the interior temperatures comfortable.
Passivhaus Open Days allow you to understand more about low energy homes
Ben and Marion are both big fans of the ‘Passivhaus Open Days’ event, which enables you to step inside completed Passivhaus or EnerPHit projects. This is a great way to experience the indoor environment and meet homeowners or professionals who have been involved.
“I’d encourage you to take advantage of these events… you can just make up your own mind.”
Jeffrey Hart from the Earthen Floor Company gives us the lowdown on natural earth floors, explaining what the components are, how they are mixed and the process of installing them. He also outlines the benefits and limitations, and highlights what makes them a great choice for an eco home.
Interview with Jeffrey Hart
Jeffrey Hart got into natural building in Oregon, USA, where he was an apprentice of earthen floors expert Sukita Reay Crimmel. He spent five years constructing various buildings and installing earth floors in each of them, before returning to the UK. Although he started out as a ‘generalist’ natural builder, as demand grew, he found himself focusing exclusively on earth floors through the Earthen Floor Company. He credits Sukita’s influence for both the modern earth floor technique and the resurgence of this historic building method.
Earth floors have been used for centuries
Historically many buildings would have had an earth floor just because it was the ground beneath the building. At some point, people realised that cow dung reacted with the earth to make it a harder, more waterproof surface. It was also noted that when blood fell onto the floor of farm slaughter houses it made the earth rock solid, so over the years different methods have been used to make the floors harder and more durable. Sukita developed a way to use linseed oil to seal and harden the clay, making it a lot more palatable for the modern world and the way we live now.
All earth floors have a binder, an aggregate and fibre
Earth floors – also known as earthen, cob or adobe floors – all have a binder, an aggregate and fibre. In Jeffrey’s case the binder is clay, the aggregate is sand and the fibre is either straw or hemp.
The process of making an earth floor is similar to that of a concrete or limecrete floor, but clay’s ability to hold together is lower than lime or cement, which is why linseed oil is added.
“The linseed oil turns the floor from something that’s relatively soft and quite easily damageable, to this hard-wearing, leathery rock.”
Earth floors can be structural or just the top coat finish
An earth floor can serve as a thin finish over an existing concrete, limecrete or even timber floor, or it can be built up as a full‑thickness slab. The minimal approach involves a 20 mm top coat, while the full build‑up typically incorporates foam‑glass insulation, optional under‑floor heating, a rammed‑earth base and a top coat.
Jeffrey’s preferred full build-up
Moisture must be managed to avoid problems
Moisture is a critical concern for earth floors and Jeffrey will use membranes if damp conditions exist and foam‑glass insulation as it acts as a capillary break, preventing upward moisture migration. It is also important that the floor dries out sufficiently before the linseed oil is applied.
Linseed oil is used to cure and harden the surface
Linseed oil is the “magic” component that transforms a relatively soft, clay‑based mix into a hard‑wearing surface. Once the clay dries, the oil polymerises, linking long‑chain molecules to create a leathery, rock‑like finish. Without sufficient oil penetration, the floor remains soft and prone to damage. The oil also imparts the characteristic warm brown hue that many owners associate with earth floors.
The embodied carbon of earth floors is extremely low
Switching from a conventional concrete floor to an earth floor can reduce embodied carbon by roughly 83 % (according to calculations using the BEAM Estimator). The reduction stems from using locally sourced clay and sand, eliminating the need for high‑energy cement, and the floor’s ability to be broken down and returned to the earth at the end of its life cycle.
“It’s about an 83 % reduction if you were to swap like for like.”
It is possible to use clay from your building plot
If you’re digging the foundations of your house and the spoil is clay, one option is to reuse it in your floor. Jeffrey believes this is the ultimate local and sustainable floor, but there are a few considerations. Most important is to test the soil to confirm that it is clay rather than silt, which lacks the necessary binding properties. Tests assess shrinkage rates, strength, and colour consistency. Variability between layers can lead to inconsistent performance, so careful excavation and sampling are essential. Unfortunately, using local clay isn’t necessarily cheaper because of the required testing and processing, so the Earthen Floor Company offers pre‑bagged mixes with clay sourced from reliable brickworks and pottery suppliers.
A lot of the cost is down to the labour
The current rate for a finished earth floor from the Earthen Floor Company is £160 per square metre for the top‑coat package, which includes materials, labour, buffing, and waxing. Prices vary with location because of the extra travel but if money is tight, self-builders can do the final oiling and waxing themselves.
You can’t walk on the floor for a month while it’s drying
Although an installer might be able to cover 10 m² per day the whole floor must be completed in a single day. This means multiple installers coming to site, the number depending on the size of the floor. After the mix is laid, the floor must dry out before the linseed oil is applied. The drying time depends on ambient temperature, humidity, and air flow; heaters and fans can help accelerate the process, but Jeffrey recommends not trying to speed things up too much as there can be unintended consequences. Once dry, the floor is oiled and then left for a further 14 days to harden.
“From install to you being able to use the floor it’s three weeks if everything goes well.”
Underfloor heating works well with an earth floor
Earth floors store heat efficiently, making them ideal for radiant heating systems. The heating pipes are usually positioned between the insulation layer and the rammed‑earth base, though some projects place them higher in the slab for a faster response in properties that may not be used all the time (such as holiday lets). The thermal mass of the earth floor prolongs warmth after the system cycles off, reducing temperature swings and improving comfort.
Repairing minor damage to the floor is quite easy
A well‑installed earth floor would be expected to last at least 30 years, becoming more beautiful as it ages. If you damage the floor, making a dent or chip, it’s actually not too difficult to remedy. By crushing leftover “biscuits” (small pieces of the original mix), mixing them with oil, you can fill the crack. While repairs are relatively seamless, they may be visible in certain light conditions. To protect your floor it’s a good idea to oil and wax it as part of the maintenance cycle; the oil’s polymerisation continues slowly over the years, gradually increasing hardness.
“We make little biscuits from the mix leftovers; they’re used to patch dents.”
It is possible to choose the colour of the floor
The natural colour of an earth floor ranges from earthy browns to greys, dictated by the clay’s mineral content and the colour of the linseed oil. To achieve brighter hues, pigments can be blended into the mix, producing uniform colour throughout the slab. Alternatively, a coloured hard wax applied as a surface finish can modify the appearance without altering the underlying material, though this layer may need to be reapplied every couple of years. Most self-builders prefer the authentic, warm tones, but designers increasingly want something bespoke.
“People are becoming more aware of this material now; it’s no longer just a niche.”
There are lots of reasons to love earth floors!
As natural materials are much more accepted these days, earth floors are seeing a revival. Jeffrey has also been doing his bit to train the next generation of installers. He is trying to make earth floors as accessible as possible as he really believes in them. They look beautiful, they feel incredible under your feet, they soften sounds and are good in terms of carbon emissions.
“And at the end of the product’s lifespan, you can break it all up, chuck it in your garden, and it will break down to be just earth again.”
Ben Adam-Smith shares a few thoughts about what to look for in a plot of land for a low energy house build.
Start with realistic expectations
Ben starts the podcast by sharing a few pieces of advice about the whole exercise of looking for land:
There is no such thing as a perfect plot. Chasing an ideal site can drag the search out for months or even years, so it’s better to accept that compromises will be necessary.
Remember how the design process works. You don’t start with the house design and then hunt for a site that will accommodate it; instead, identify the constraints and opportunities of each site. Good design embraces these and responds to them.
Recognise that this is a lengthy process. Sometimes it can happen quickly but brace yourself for a journey that could take months or even years.
Be flexible. This allows you to make the most of the opportunities.
The good news is that those who stay determined normally find a building plot in the end.
Define your needs versus nice‑to‑haves
Splitting your requirements into “needs” and “nice‑to‑haves” is a great way to prioritise. Also identify what you can do without. This information can help you calculate what size plot will be enough. For example, a good sized house doesn’t need an acre and could fit on a plot a fraction of the size. However, if you also want to be set back from the road, have a driveway, garage, garden, patio or paddock then this will quickly add to the spacial requirements.
Find a neighbourhood that aligns with your values
Choosing a location is deeply personal, and will be about finding somewhere that resonates with you. Consider proximity to work, schools, medical facilities, shops, and leisure activities, as well as the overall safety and vibe of the neighbourhood. Visiting the area at different times of day reveals hidden issues such as traffic noise, smells, or activities that could lead to unruly behaviour. Community values matter too; a plot embedded in a supportive, like‑minded neighbourhood can enhance long‑term satisfaction. Just be careful not to restrict yourself to a tiny search area, as this can dramatically reduce the pool of viable sites.
Make sure the plot has good solar access
If you want to build to Passivhaus standard then solar access is really important. In the Northern Hemisphere south facing sites are ideal because you can maximise the gains in winter whilst also easily managing shading in the summer. Another advantage is that if you plan to install solar photovoltaic panels then these will also be more productive on a south facing roof.
Be realistic about what you can afford
Sometimes our dreams go beyond our financial means, so it’s really important that we take in the whole picture when considering our building plot. Don’t forget that there is an equation to value land:
Land cost + construction cost + 20‑30 % profit margin ≤ value of the finished home
So land price is only part of the equation; you’ll have to factor in professional fees, material costs, groundworks, utility connections and a contingency budget. Regularly updating a spreadsheet with quotes and estimates keeps the project grounded. Ben also highlights the psychological toll of overruns, noting that stress, health, and relationships can suffer if finances spiral out of control.
Don’t buy a site without planning permission
For first-time self-builders it’s a really good idea to buy sites that already have planning permission for a dwelling in place. Normally the drawings can be swapped out for the design you want so long as you stick within the key parameters.
When you’re looking for sites the main types you will come across are greenfield, brownfield, infill, and replacement dwellings. Greenfield sites rarely get planning permission because they are assigned to agricultural use whereas sites within a settlement boundary stand a much better chance. Checking your local authority’s planning portal for recent applications is a good way to gauge what kinds of projects are getting approved in the area.
Understand the additional costs of sloping sites
Flat land is generally cheaper and simpler to develop, while slopes introduce extra costs for foundations, retaining walls, and drainage. Ben references Mark Brinkley’s “slope law,” which quantifies cost increases for every five degrees of gradient. In other words the steeper the slope the more it’s going to cost.
However, a sloping site can also provide attractive views and unique architectural opportunities, such as an “upside‑down” house. Understanding how you’ll manage excess soil (“spoil”) from excavation is essential; disposal or reuse plans affect both budget and environmental impact.
Find out what’s in the ground and around the site
Soil composition—clay, chalk, sand, gravel, or rock—directly influences foundation design and drainage solutions. Ben shares anecdotes about historic mining areas where unexpected subsidence posed serious risks. One option is to commission a geotechnical survey, which involves boreholes, trial pits, and laboratory testing to produce a detailed ground‑water and soil‑strength report. Local engineers and contractors can interpret these results to optimise foundation type and avoid costly redesigns later. Additionally, finding out what the site was used for before may put your mind at ease when it comes to possible contamination. There could also be ecological considerations, such as protected wildlife (e.g., newts, bats), and trees that you can’t remove (tree preservation orders).
Ensure the site has legal access
Legal access is essential; a “ransom strip” or missing right‑of‑way can render a plot unusable without negotiation. Ben recounts the situation at Denby Dale where the Tunstalls were forced to purchase an additional piece of land to gain access to their proposed site.
Assess whether the site has power, water, sewerage and broadband connections as extending services can be a significant expense. Public footpaths, private roads, and other legal challenges must be identified early, and a solicitor familiar with land should verify that all rights are documented. Ben also notes the importance of planning for delivery vehicles and construction traffic when evaluating access routes.
Add in your gut feeling about this opportunity
If you’ve whittled it down to a favourite plot then are you getting excited? If a plot has lingered on the market for a long time, or if a site feels “off” during a visit, it may signal hidden problems. So walking the site at different times, speaking with neighbours, and observing any recurring nuisances such as noise, anti-social behaviour, or flooding will give you a better grasp of the site’s pros and cons. When doubts arise, it’s sometimes wiser to walk away than to convince yourself it’ll all work out. Ben concludes by encouraging listeners to leverage the free “finding land” course and to join The Hub to get more support.
Es Tresidder from Highland Passive explains what an air-to-air mini split heat pump is, why he believes it’s a good choice for heating a high performance home and the various pros and cons of going down this route. He also reflects on one of the toughest stages of his retrofit when they took the roof off the existing dwelling and then faced torrential rain.
Interview with Es Tresidder
Es Tresidder is a certified Passivhaus Designer with over a decade of experience in low energy buildings. His consultancy Highland Passive helps self-builders and retrofitters create better homes, that are healthy, comfortable and energy efficient. He’s also been working on various projects for John Gilbert Architects over the years, and he’s a regular at House Planning Help as part of our ‘ask the expert‘ team in The Hub.
Es has been on the podcast before, explaining how he upskilled in DIY during his retrofit project. In this session he’s reflecting on the whole process, including a key challenge he faced with water damage, and he’s going to go into detail about how he heats his home with an air-to-air mini split heat pump.
Es is a regular in The Hub where he helps answer questions on building physics and retrofit
Vehicle-to-load allows you to use an electric car’s battery to power external devices
This podcast was recorded during a power cut and was only possible because Es has an electric car capable of vehicle-to-load, which means that you can plug an adapter in to where you normally plug it in to charge, and then plug a three pin, normal domestic plug into that, and run that into your house. He explains that you can’t power your whole house, but you can take three kilowatts from it, which he was using with three or four extension cables strewn around the house, to power the fridge freezer, the dishwasher, the Wi-Fi, to charge computers and even to make a loaf of bread overnight!
“…logically, you know that electricity is very, very useful in life, but life just becomes much harder as soon as you don’t have electricity.”
When Es put the services into the house, he created a service void, which is effectively a pipe that goes through the external wall with an airtight membrane on one side and a windtight membrane on the other. This means he can add new cables into the house and make them airtight easily. He did this when adding solar PV to the roof and now he’s done it again, putting in a permanent extension cable that can connect to the car, ready for the next power cut.
Home battery systems with ‘island mode’ help you operate independently from the grid during a power cut
Es explains that domestic inverters shut down when the grid fails, preventing the house from drawing power from solar PV panels during an outage. However, if you have a home battery system you can pay extra so that you can island from the electricity grid, which would happen automatically during a power cut. However, domestic batteries are only around seven to 12 kilowatt hours, so if it was January or February, with little solar power generation, you’d quite quickly go through your battery’s power, even in a Passivhaus. A car battery is much bigger, around 77 kilowatt hours, which would last several days during mid-winter, running heating as well as everything else. Another advantage is that if the power cut lasted much longer, he could just drive into town to a public rapid charger and top the car back up.
Getting the MVHR back on was a priority because it immediately improves the health and comfort of the home
Es says the MVHR has a really small energy requirement and is beneficial in lots of ways, so it was the first thing they plugged in. Until that point they had been keeping windows open for ventilation and, with an outdoor temperature of 12-13 degrees, the temperature inside had dropped down to around 17 degrees.
The existing dwelling before any alterations
The completed project
Photography by Alex Trowski, commissioned for a case study in Passive House Plus Issue 50
The retrofit, extension and remodel has made the whole house work better as a home
Es’s house was a 1975 timber-frame build of one and a half storeys, where the first floor rooms felt quite pokey. So the strategy was to take the whole first floor off and rebuild it as a one and three-quarter storey house. This may not sound like a big increase, but Es says it gave a lot of extra floor space on the top floor, with enough for an extra bedroom, and an increase in size for the other bedrooms. The floor plan just worked much better.
The upper floor is a new build Passivhaus, with an I joist timber frame sitting on top of the existing structure, which was quite complicated to do. Downstairs is a retrofit of a 100mm timber frame house, where the plasterboard was taken off and insulation put between the studs. He then added another 40 mm of wood fibre insulation board, an airtightness membrane, and then outside of that is white rendered blockwork. There’s a cavity between the two. As a Passivhaus Designer, Es did all the energy side of things and a lot of the retrofit work himself. The new build was carried out by a local contractor.
The project involved removing the pitched roof and extending upwards
Keeping a flat roof dry is incredibly difficult
This project required the first floor and roof to be removed, which is slightly unusual. When they were looking at the options, one way to keep everything dry was to put up a massive tent over the whole structure, but this would set them back £30,000. The builders, however, were confident that they could keep the water out because they had done this many times before. There was also the fact they would be doing this in May which is statistically the driest time of the year in Fort William. Unfortunately the weather did not play ball and it was an unusually wet month. Es also points out that although the builders take off lots of roofs they probably don’t remove the whole structure leaving effectively a flat roof to keep dry.
So it just became impossible to protect the structure from the torrential rain. Es had already insulated the ground floor and achieved good airtightness but the rain soaked the floorboards and insulation, forcing him to strip them out and replace everything.
“You don’t want to install any insulation until the building is watertight.”
A lot of insulation got waterlogged and had to be replaced
Sequencing the work differently would have avoided damaging the insulation
If doing the project again Es would not necessarily pay for the giant waterproof tent but he would sequence things differently. The work downstairs had been done first to ensure structural stability for the new first floor and roof. However once rain had compromised the work, they had to go ahead without the extra racking boards on the walls anyway or the racking strength from the floor. He would therefore consult a structural engineer to look at any structural elements that could be done without involving the insulation.
The unit inside the house
An air‑to‑air mini split heat pump is a cost effective way to heat a low energy home
For Es, a heat pump is an obvious choice over direct electric resistance heating. However, instead of a conventional air‑to‑water heat pump system, Es chose an air‑to‑air mini‑split system. He explains that this is like an air conditioner, which usually pumps heat from inside to outside a building, but can also be used to pump heat from outside to inside a building. They have a similar efficiency to an air-to-water heat pump, but are much cheaper to install, because there’s no need for radiators or a wet system. The mini split has an outdoor unit and an indoor unit, with refrigerant lines between the two. The unit and installation cost was around £1,500 compared to £12 000 for the air‑to‑water system. Es is clear that this system is great for a Passivhaus but wouldn’t work for a normal new build house as it only delivers heat into one room and relies on heat spreading to other rooms.
The unit outside the house
Reversible operation provides useful cooling in heatwaves
Mini‑splits can run in reverse to deliver modest cooling, which has proved handy for Es during a heatwave which coincided with the midge season (when they don’t really want to open any windows) and a large group of friends staying over and thus raising the indoor temperature.
Sizing the mini split above peak load ensures comfort in cold snaps
The house’s peak heating demand is around 1.3 kW and by selecting a 2.7 kW mini‑split Es has provided a comfortable margin, which allows the system to cope with occasional freezing cold days without needing supplementary electric heaters. In cold weather he will run the system overnight when electricity is cheaper, so increasing the temperature in the main parts of the house, whilst the bedrooms stay cooler. Once the doors are open the heat can spread through the house. He admits that having his office in his bedroom means occasionally it can be cooler than he would like and so a small electric heater would probably be a good addition.
Photography by Alex Trowski, commissioned for a case study in Passive House Plus Issue 50
Locate an air-to-air mini split system in a large open area
Es explains that the mini split system needs to be in a space big enough to deliver a lot of heat into it, before warming that space to above the set point temperature. A small room would reach that temperature quickly then the system would shut off and so not provide enough heat for the rest of the house. The indoor fan also produces a low hum comparable to a refrigerator, louder than the house’s MVHR, so you need to place it where the noise won’t matter too much. Es stresses that whilst the MVHR supplies fresh air, and recovers heat it only moves a small amount of warm air between rooms. Keeping interior doors open lets the warm air from the mini‑split circulate more effectively.
Grants favour air-to-water systems, but air-to-air systems may still be cheaper
Even though Scottish renewable‑heat grants are available for air‑to‑water heat pumps and not for air‑to‑air units, Es feels the air‑to‑air solution may still be cheaper. The grant system also involves a lot of paperwork and restricts you to using MCS certified contractors, who are not necessarily the best. For a Passivhaus going down the air-to-air route also means you keep things simple.
A standalone hot water pump works alongside the air-to-air system
Whilst air-to-water heat pumps can also be used to supply hot water, an air-to-air mini split system is just warming the air in the house. So Es has installed a heat pump water heater, which is a 200 litre insulated hot water tank with a small heat pump on top. They are normally ducted to the outside to bring fresh air into the heat pump, the heat pump takes some heat out of that outdoor air, and then it ducts the exhaust air back out. Es has set his up to take heat from the house, which gives some free cooling in the summer and a much faster reheat time in the winter. It’s also easier from an airtightness point of view as it is not ducted to the outside at all. In the winter, the water heat pump is slightly cooling the house, so the mini split has to work a bit harder, but overall, it is still very efficient.
Living in the house has been amazing
The house before Es started had quite serious mould and damp problems. They were always a bit chilly in winter and couldn’t dry things because there was no reliable ventilation, and the house wasn’t warm enough. Now things are completely different.
“It’s hard to remember how it was before, because it’s just so nice now.”
The house is warm and comfortable all the time in every room. Es believes it’s almost more impressive in hot weather than it is in cold weather, when you expect it to be warm. Es says that the first summer they moved in, they had two separate weeks of more than 28 degrees as peak temperatures in the afternoon. And in those conditions, the house was at 23 degrees, and it felt like walking into an air-conditioned space. It has really improved the quality of life. The air is clean and just walking outside the house, Es immediately notices if the neighbours oil boiler is running or there’s a coal or wood fire on locally. He thinks his sense of smell has improved, because he’s used to clean air and the house smells fresh all the time. The best thing isn’t the bills, but it’s the most quantifiable thing. He’s reduced his heating bill by at least 80% while also massively increasing the average temperature of the house.
“After one full year of monitoring we have spent £175 on heating and hot water for a family of five, which is remarkable.”
Having spent the last few years working within the Ministry of Housing, Communities and Local Government, John Palmer explains how building regulations are made and what their role is within the construction industry.
Interview with John Palmer
In 2012, having served as an engineer in the Royal Navy for 16 years, John Palmer pivoted into the construction sector. Over time he gained his Passivhaus credentials, built a high performance home and also spoke to us about the impact of setting an energy target. He then joined the Passivhaus Trust and was trying to lobby the government to do great things for energy efficiency and housing when an opportunity came up in the Ministry of Housing, Communities and Local Government. He moved into a policy position there four years ago, looking at the Future Homes Standard and Energy Performance Certificates. John has recently taken a secondment to work with the Building Safety Regulator on some of the processing of Building Control applications.
British building regulations date back to the Great Fire of London
The origins of building regulations can be traced back to the Great Fire of London in 1666, which resulted in banning timber in the external construction of homes in London. More recently, the building regulations, became not just for fire and structure, but for many other aspects like energy efficiency and moisture, so that there are now 18 parts to the UK Building Regulations.
Each regulation will require a certain outcome to be achieved
John explains that the Building Regulations are primarily outcome-based regulations, which means that they don’t set prescriptive requirements for how things should be built. For example, Part B relates to Fire, with outcomes to build things that don’t spread fire to other buildings, and that can resist fire for long enough for people to get out. This could be met in a variety of ways.
The Building Regulations set minimum standards for life safety
The primary intent of the Building Regulations is to set minimum standards for life safety and that’s where most of the regulations are targeted. John explains that it’s not just about structural collapse and fire, which are obvious threats to life safety, but also longer-term threats such as poor internal air quality and moisture levels within buildings.
Over the years, additional regulations have been added that go beyond this. For example, broadband services and electrical vehicle charging have their own part of the regulations.
Events often drive significant changes to the regulations
The Grenfell Tower tragedy in 2017 had a huge impact upon building safety in the UK, notably prohibiting combustible materials from being used in the external walls of buildings more than 80 metres high.
Whenever government decides to bring in a change to the regulations, there is a lengthy process involved to work out what the impact of that change might be.
“Is this going to do what we would like it to do? Is it going to be enough? Are people going to try and circumvent it?”
There can also be unintended consequences to consider.
“What else would people use? What are the non-combustible materials? Are there enough of them in the supply chain? What does that mean for the quality of design or structural strength?”
All these second order effects need to be considered during the policy-making process to ensure the unintended consequences have been explored, and any risks are accepted or understood.
John Palmer giving a keynote speech at the ASBP Healthy Buildings Conference
Policy changes stem from the government of the day
Any changes to the Building Regulations will be initiated by the government of the day, who will ask the civil service for an assessment of the impacts. This will include the second order effects that might occur from a change to the regulations, such as to supply chains and labour markets. Ministers will be looking at how they will balance the impact of the proposed change to the regulations versus other competing government priorities. In some cases, a minor change might be relatively straightforward, with little or no impact on anything else, in which case it would be implemented. Other more significant changes might have bigger impacts on the cost, complexity or material supply chains of new homes. Government ministers will take a measured decision as to whether to press ahead, postpone it or do a lesser version of the change in order to lower the impact. It becomes a proportionality and judgement call for the government of the day at that point.
Policy‑making is a multi‑stage, consultative process
John shares an example of how a regulation might be created and the process it would need to go through. So, it might be proposed that we should paint all our houses pink in the future! This would then be assigned to a relevant team in the civil service, and they would look at how it might work and form some options of how it might be achieved. Building regulations might be one of the options. They’ll look at the potential benefits of pink homes, they will put that to ministers, and create a consultation, because normally there has to be input from the public or a stakeholder view for any proposed policy change. The consultation will have to get ministerial approval and cross government approval. It then gets published and runs for a minimum of three months, at which point it will be evaluated. The results may lead to more questions that need answering and so that might require further work. The options then go to ministers, who may ask further questions or want different options. If an option is approved that requires a change to the regulations themselves, not just the guidance, then a statutory instrument needs to be drafted by lawyers, checked several times and then time found for it to be laid in Parliament. In other words, it’s not a trivial process to update the regulations and can take anywhere between 12 months to two years to put in place.
Other mechanisms could achieve the same outcome
The other option is to encourage the desired outcome. So, in our example there could be an advisory that encourages all homes to be painted pink, and there might be a scheme whereby discounted rates on pink paint from a local retailer has been arranged. This whole approach could be put in place in two or three months.
“The carrot encouragement, optional, discretionary type approach to getting things into the built environment is always much quicker than the stick approach of actually going through and making changes to the regulations.”
Approved Documents provide statutory guidance on how to meet the regulations
Accompanying the Building Regulations is a set of statutory guidance, known as the Approved Documents. John explains that Part A of the UK Building Regulations, which is a statute in law, has an accompanying Approved Document A, which is the statutory guidance that sets out how that part of the building regulations may be complied with in typical situations. That means that someone designing a building can look at that Approved Document and know that there is a clear path to compliance. John says that if you are doing something slightly unusual, say an innovation, that might not be covered by the Approved Documents, then it is the building regulation itself which must be complied with.
Regulations will always evolve
In an ideal world, all regulation is necessary, all regulation is minimal, and all regulation is proportionate. These are the tests that government applies when introducing new regulations. However, things do change over time and regulations which were previously proportionate and made perfect sense, may no longer do so. This means there will always need to be a review and update of the regulations.
Regulation is nothing without enforcement
Part of creating a regulation involves working out how the government or the relevant regulator will know if that regulation has been complied with. Also they must consider what action to take if the regulation is breached.
“As part of the policy process, you would define what the sanctions would be for organisations or individuals that didn’t comply, which might include fines or coming off registers.”
Building Control is the main mechanism in place to ensure that people are compliant with the building regulations.
New regulations may have a long lead in time
Where the impact analysis has been sufficiently confident that the regulation is going to work, it’s not going to cost a fortune or result in supply chains collapsing, it can be put in place in fairly easily. Where it’s less clear-cut, different approaches can be taken. One of the primary routes is to give a long lead in time to allow the industry to plan and adapt. This way it’s also easier to address unintended consequences if they arise.
John tells us it can be more difficult for the government to run small pilot projects as there is a tendency for people to think a proposal is definitely going to happen, which can result in unintended consequences for segments of the industry.
Incentive schemes can also encourage behaviours
Incentive schemes are another mechanism that government uses to encourage certain behaviours. They’re not necessarily regulated in the same way as by their very nature, they’re never going to be enduring. They are used to encourage either innovation in technology, market shifts or consumer behaviour, with solar panels being a good example. When solar panels first came in, they were prohibitively expensive, so incentive schemes mitigated against the high costs, and made them more attractive to homeowners. When the price of solar panels dropped to affordable levels, where payback periods without incentives still made financial sense, the scheme had done its job and that money could be better targeted elsewhere.
Digital tools and automation are the future of compliance
Currently, implementation of the Building Regulations relies on individuals becoming experts in compliance, which may not be the optimal way of doing it. John tells us that an Approved Document review panel has just been set up to look at how the documents are formed, communicated and relate to each other.
“For example, is there a single definition of a dwelling that’s used across all the Approved Documents, or are certain words used in different ways in different parts?”
John says this does happen, so communicating them more effectively and setting them out in a different way might be an option. Digital processes may also be embraced more in the future, perhaps becoming more integrated into CAD design systems.
“Where regulations talk about heights, clearances, etc. could it be possible to have a level of automation? Or maybe a red, amber, green indication that you are compliant with the Building Regulations? Those kinds of things could make a big difference and create a better starting point for a designer to feel confident they’ve designed something in accordance with the building regulations.”
Sometimes you may need specialist input to check you are compliant with the Building Regulations
When building your own home or having your own home built, you can use either the Local Authority Building Control or a registered Building Control private provider. As part of your project, you will submit evidence to demonstrate that you’re compliant with the Building Regulations. This will include documents and drawings showing the structure of the build, fire safety, etc. For a typical self-builder, this will be quite specialist information that will require technical input. For John when building his own home, he was keen to have an input over the design materials and felt qualified to have a view on those. However, when it came to other parts of the Building Regulations, such as the structure and fire safety he knew he needed to bring in expertise.
“That specialist input may sit with your architect or designer along with structural engineers, possibly fire engineers and energy assessors when required.”
New building standards apply to some but not all aspects of retrofit
John outlines how new build standards, don’t necessarily apply in their entirety to retrofits, because you’re starting with something already built. For example, energy performance will be looked at differently in a retrofit, where you can’t necessarily decide the form factor, the size of the windows or amount of glazing.
There is also a basic principle of non-worsening in the Building Regulations that applies to retrofits. If you’re redoing an entire wall, you might need to bring that up to a required standard for thermal performance, whilst other aspects of the Building Regulations might not apply. You don’t necessarily have to make your refurbished building as accessible as a new building, but you do need to make sure that it doesn’t get less accessible, which is the non-worsening principle. Your Building Control body should be able to advise on exactly what level you need to reach in certain areas and whether other things would be subject to non-worsening, in which case you can leave them as they are.
There’s likely to be a more coherent approach to housing as a system
John concludes by noting that many different pieces of legislation have grown up organically over time, which drive outcomes in the housing sector and so it is a complex area. He thinks that the regulatory landscape will start to evolve to a more coherent approach towards housing as a system. This could go all the way from deciding what you’re going to build, planning, designing, building regulations, and once built to its occupation. All those regulatory regimes could work together a bit more seamlessly, and a bit more effectively.
“So that the end result – which is people living in high quality, safe, decent homes, beautiful homes that you know are a pleasure to live in – becomes more the norm.”
Will South from Etude takes us step-by-step through the retrofit of his Victorian terrace house in Brighton, which has improved the health, comfort and energy efficiency of the property.
Interview with Will South
Will is a mechanical engineer, working at Etude to make buildings better through reducing energy consumption and carbon emissions, an approach he has carried over to all the places he’s lived. With his most recent move he had in mind a retrofit project right from the start. He wanted to be in the middle of Brighton, close to the railway station and the coast, in a modest sized home. So he chose a Victorian terrace house, originally a two-up two-down that he could retrofit to the level that would be right for the building.
Many period properties have common traits
Will’s house is a classic Victorian terrace design, where there is space for you to take off shoes and coats just through the front door, the stairs are in front of you, then there’s the living area on one side and a kitchen all the way through at the back. Upstairs, there are two bedrooms and a bathroom. Will describes it as a simple layout with a nice flow and high ceilings, even upstairs, which is more unusual.
Deciding how deep to go with your retrofit is a personal choice
A big part of Will’s day job is working on Passivhaus projects, but here there was a question around the right level of retrofit for this type of property.
This project has also made him realise that maybe not all homes need to have as deep a retrofit as he used to think, and that heat pumps are more than capable of heating the majority of homes with few changes. However, he knew he wanted to take it further and make the house as comfortable as it could be. With his experience in ventilation systems, glazing specifications, insulation, etc. nothing was off the table.
“We’ve done everything: walls, roofs, floor, new ventilation system, new windows, but a lot of it is as an experiment to show how it could be done.”
Watch an EnerPHit retrofit of this Victorian home in The Hub.
Decarbonise your heating by moving to a heat pump
One key move Will wanted to implement to lower his carbon emissions was to switch from a gas boiler to a heat pump. For most homes, some fabric measures may be needed, often topping up loft insulation, improving windows and upgrading radiators. Anything after that will continue to improve comfort levels, reduce bills and increase resilience for the future.
Create an overall plan for your retrofit
Will started with his dream end point, irrespective of budget, to come up with an overall plan for the retrofit. For example he has not installed solar PV as part of the project but he has made allowances for it as a future addition.
With a solid retrofit plan, he then examined the priorities. There was leak in the roof and a rear extension, where the floor and the roof were in a sorry state. Generally, starting with the roof is a good strategy, which for him meant redoing a parapet then making sure the party firewalls and the chimneys were in a good state before he did anything else, so that the building had a good chance to stay dry.
Having a good ventilation strategy is essential on a retrofit project
Will tells us that although it took a long time he ended up doing everything in almost one go. If you have to do a phased retrofit, you need to make sure that the building is left in a good working state at the end of each stage. The main risk is around ventilation and managing moisture in the building, and you need to be careful you don’t seal up the building or insulate it in one part without dealing with the ventilation. A ventilation strategy is often a priority and if the end goal is a mechanical system, then get that in early, so you’re already managing the moisture levels.
SketchUp was used to create drawings for the project
As a consultant Will knew what was needed but he wasn’t used to doing the drawings himself, so that was a bit of a challenge. He used SketchUp to create a model of the house, including drawings for the existing building and the proposed building. Being in a conservation area, planning permission was needed for replacing windows at the back of the house, and altering the roof-scape slightly to fit the heat pump at the rear, which led to more drawings for the planners. In the end he made a full set of drawings to help him work out what he was going to do and allow him to communicate easily with the contractor.
Will imagines that in the future there will be templates for every building type, that you would alter to reflect your own situation. There’s already a good website called retrofit.support, which has a pattern book of details that give you a place to start.
Create a detailed cost plan
Will paid a cost consultant who specialises in housing to provide him with a full cost plan. This gave him a long list of everything needed, with a starting point for all the prices, giving a good feel for what it would cost if he did everything. This service cost around £400 but was invaluable.
The costs for construction broadly came in as expected. He imagined that there might be a big cost differential between materials but in actual fact he was dealing with such small areas that the cost was all in the labour.
Budgeting for the internal finishes was much more difficult as costs varied dramatically, particularly for bathrooms and kitchens. So unless you have an example of the product that you want to use, it can be hard to budget accurately for this stage.
Different insulation strategies have been used around the house
Will explains that even though it’s a small building a variety of strategies have been needed to insulate the roof, walls and floors. Initially they planned to live in the house while the retrofit took place. The first phase was going to be the rear return, with the kitchen and the bathroom. The kitchen ceiling was falling in and the bathroom ceiling looked worrying, so both needed attention.
The building has all sorts of roof types, which is not ideal. There is a small parapet at the front which has got insulation between the rafters and a lead roof. Then there’s the main loft which has mineral wool insulation, the rear return which has Larsen trusses, filled with insulation in the pitch, and a small flat section of fibreglass roof which has got the heat pump on it.
“Generally, starting with the roof is a good strategy. An old fashioned building has a good hat and good boots.”
Planning restrictions also had an impact on the insulation strategy
Being in a conservation area an internal wall insulation strategy was adopted at the front of the building, using 80mm wood fibre board. There is a bonding coat underneath, made by Baumit, which helped create a flat base for the boards to go on to and added an extra 10-20mm of insulation.
At the rear of the property they were allowed to insulate externally and have used cork, which was chosen because it deals with moisture better than some other products. The external wall insulation is taken below ground to the foundation with EPS.
The floor became a bigger project than originally planned
While Victorian properties are highly desirable today, when they were built they were thrown up quickly and cheaply so there were a few surprises lurking. When they took up the floor, they found slim 3-inch joists sitting on continuous bungaroosh, which was just piled up chalk. As they were able to move out of the house for a few weeks they could tackle the floor in a more significant way.
It involved taking out all the timber and the dwarf walls, scraping back the chalky base to create the space needed for the floor build-up. EPS was directly put onto the sand blinding, then a plastic DPM, and finally a concrete screed with underfloor heating. It’s a simple build-up as there’s no structure sitting on it. Will would have liked to have reused the original floorboards on top of the screed but was advised against it.
The sash windows have been improved
While Will had more freedom at the back of the house, where he installed some triple-glazed units, at the front of the house there were restrictions. He also did not want to get rid of the beautiful period sash windows. So he has replaced the sliding part of the sash and put in vacuum glazing. The boxes are original although he has added a draught strip to improve airtightness. He’s used a foam filled rubber draught strip, a type more often used on a casement window, which is more robust and gives better airtightness, but it makes the windows a bit stiffer. As all the windows are wooden, they will need maintenance and Will suggests to always repaint them just before they look like they need painting!
Having a continuous airtightness layer was easier said than done
The strategy at the beginning was to identify where the airtightness line would be for each part of the construction. Will realised that they would be able to achieve it for some parts, but in other areas they wouldn’t be able to get into places to create an air barrier. He estimates that he got around 75% of the way with airtightness and to get any further would probably have meant gutting the whole house and starting again. The intermediate floor and all the internal walls stayed where they were, but the external wall finishes were removed allowing for bonding of the insulation, creating continuous runs to tie into the next airtightness material and into the windows. The damp proof membrane underneath the screed on the ground floor comes up the inside of the wall and is taped on there. In the loft Will put a membrane over the top of the joists, cut it around all the trusses, taped it and then put the loft insulation on top of it. It was very difficult to tie it into the top of the walls right into the eaves where access was limited. The eaves were extended very slightly at the back of the house to accommodate the external wall insulation. This meant the last two tiles were off for a time and Will used the opportunity to do more taping. His approach was to use membranes only where there was timber, and then everywhere else to use a wet lime product.
Before the sash windows were replaced, Will got an air permeability of 2.1 which is three air changes per hour at 50 Pascals, which he was pleased with and was in fact the number he’d put in his PHPP model. He hopes it will have improved and is going to get another air pressure test and more thermography in the winter.
MVHR can usually be integrated seamlessly into an existing home
Installing mechanical ventilation with heat recovery can really improve the indoor air quality in an existing dwelling. It manages moisture in the home, allowing you to do things like cook or dry washing without consequences. And Will believes that there is always a way of designing a system into an existing home and figuring out the duct runs, etc. It just takes careful planning.
The benefits of MVHR are noticeable even in a leaky home
Even if the airtightness has not been addressed fully Will feels that installing MVHR will improve the ventilation in a house and because it has 90% heat recovery it will give some energy saving no matter how efficient your building is. If you then improve insulation and airtightness you will continue to see benefits.
A heat pump is a good choice for a low energy home
When they bought the house it had a 10-year-old combi boiler, which they could have used for a bit longer, but Will was keen to switch to a heat pump heating system. So when redoing the bathroom he took the opportunity to put a new hot water cylinder where the boiler was, because all the pipe runs link to that point. An extra motivation to get off gas was the massive gas meter that was located in the entrance hallway. He paid extra to get this disconnected and removed.
In Will’s experience it was difficult to buy the heat pump and difficult to get it installed, a view that other people have also expressed. At the time, it was also difficult to find somebody qualified to install heat pumps. In the end, his builder’s plumber carried out the work, and used it to upskill and get his MCS qualification, which was really positive. On the negative side, he hadn’t known they didn’t have MCS and so he was not able to get the boiler upgrade grant.
He had assumed that the heat pump manufacturers would know what was needed for a small home, so hadn’t looked into the detail himself. That was a mistake and the whole process got complicated very quickly. They’d assumed he wanted thermostats in lots of different places, and that the radiators and underfloor heating circuit were on different zones. Will ended up having to change things afterwards, which was frustrating. The other eye opener was just how much equipment you end up with inside the house. He had thought about a cylinder, but with unvented cylinders you also have an expansion vessel for the heating, an expansion vessel for the hot water. Then there are two control boxes, two zone valves and they wanted to put in a buffer vessel as well. It really started adding up, with a lot to fit in a small area. He recommends buying a hot water cylinder with a built-in expansion vessel, which is a bit more expensive but saves on space.
Will’s energy consumption has gone down significantly
The average temperature within the house has increased to a constant 20 degrees, which is where Will wants it to be. Gas consumption has gone from 158 kilowatt hours per metre squared per year, which was quite high, to zero.
This has however been replaced with electric heating, with electricity use now around 40 kilowatt hours per metre squared per year. This went up about 20% after the switch over to electric heating, so a much smaller uplift than the reduction in gas. By Will’s calculations his carbon emissions are down by 85%, which is significant. If solar PV was added at a later date they could be net zero.
Some of this is about how they live, with just two people in the house they don’t have huge consumption and are out a lot of the time. In financial terms their energy costs have more than halved, reducing from £2,500 a year to about £1000 a year.
Sticking to a budget is tricky!
Will sees a budget as a good tool to manage costs although he realises this isn’t necessarily what you’re going to spend. Therefore he put aside a significant contingency. For him this takes away the worry about money, which can so often cause problems.
Buying a smaller house in the first place and securing a bigger mortgage so as to free up the cash was also sensible. They had an inheritance and some savings, which essentially has all been spent on the house. It has come in at around £150,000, but this figure includes a new kitchen, new bathroom, new flooring and a lot of extras.
Replacing the suspended floor was a gamechanger
Amongst the takeaways from the project Will feels the hard work and disruption of putting in a solid floor with insulation underneath has really paid dividends. So if you have enough space to play with then this is something Will would definitely do again as it’s made it draught-free and always comfortable to walk upon.
The installation of the heat pump relied heavily on the plumber
Will was surprised that even though they had a Vaillant heat pump and used their designs, a lot still rested on the plumber. If he was doing it again Will would take more of it under his control.
Airtightness is often about doing the best you can
Will thinks he did a really good job on airtightness, but reflects upon the fact that there is always more that could be done. If he were to do it again he would use more traditional wet materials like lime-based plasters for airtightness when dealing with crumbly brickwork.
The house is now comfortable all year round
When they bought the house the structure was worrying with a bendy beam, ceilings falling down and it was very damp, with slugs behind the kitchen cabinets. During the winter they were just heating whichever room they were in and downstairs they were always aware of draughts from under the floor. There is none of that now, it feels homely and is a constant 20 degrees throughout the house all year round.
Joshua English, co-founder of Okom wrks labs shares his journey into the creation of a mycelium-based composite material, which has structural and load-bearing properties.
Interview with Joshua English
Joshua English, co-founder of Okom wrks labs describes himself as a jack of all trades with a lifelong obsession with fungi. Although he did an arts degree, he realised he loved working with numbers and so spent his early professional life in database programming. After 18 years doing data analysis and data visualisations for healthcare he started to miss the physical world. He then took a degree in Interior Architecture and Design, with an emphasis on industrial design which led to a hyper focus on materiality. A long-time carpenter, with a love of metal and concrete and the knowledge that those materials were not great for the environment, he wanted to try to find the most sustainable way to build things. When a friend introduced him to mycelium-based composites about six years ago, he took a deep dive into the subject.
Could he make a chair using mycelium-based composites that people could sit on?
In his research he came across pictures of chairs made from mycelium-based composites, but nobody was sitting on them. Could he be the first designer to make a chair that a human could sit upon? He spent six months gathering information on the technology with a plan to spend two years researching how to make mycelium-based composites stronger. He ended up finding a solution much quicker through a random application of materials left over from his first set of experiments. He then had to reverse engineer from this “mistake” to work out what had happened. It took a few years to patent this process and they are now looking to patent the material itself.
Mycelium are fungi and not to be confused with plants
Mycelium is fungi, which is in its own kingdom and not to be confused with the plant kingdom. Joshua explains that where animals engulf their food and plants photosynthesize, fungi absorb their food, so their whole lifestyle is centred around surface area. We think of mushrooms as fungi, but they are just the fruiting body, the mycelium is by far the vast majority of the organism. He compares it to an ant colony, where the individual ants are like the hyphal strands of the mycelium. A mycelium will have billions of hyphae that branch out to explore their environment. They provide a large surface area and exude enzymes to absorb their preferred food source. To do this the hyphal strands need to be incredibly strong, durable, and multi-use as well. Joshua is exploiting the capability of the fungus to create an adhesive to use as part of the matrix of a composite material. Not all fungi have the capabilities to create strong mycelium-based composites, and so far, mycologists have found that fungi that grow on trees are particularly well suited for this.
This technology is still in its infancy
The technology goes back to the early 2000s, but it has grown and developed in the last 25 years. Philip Ross, an art major at Stanford and a lifelong mycophile started to develop processes to make things out of mycelial colonies about 20 years ago. He then used mycelium blocks to create striking artworks and published his findings, which people started to notice. Some engineering students in New York, then developed a business model to use this technology to make a foam packaging replacement. They tried to commercialise it about 13-15 years ago. When researchers started to look at the key qualities of the mycelium-based materials they were impressed with its fire resistance and sound attenuation, but it was not so good structurally or when it came to water absorption. This led to them being relegated to insulating panels or decorative wall sound mitigation panels.
“And then, you have a guy like me who makes a mistake in the lab and then finds this way to make what seemed to me to be structurally sound materials.”
Turning it into a business is a huge challenge
Joshua believes that a 5 -10 year time frame is needed to go from the research phase to a commercial product. In his experience Venture Capital investors want more of a 2 year turnaround, so there is a mismatch here that needs to be overcome. Because it’s such a new technology there is a lot of siloing happening along with a push to early commercialisation. There is also a big rush to patent the materials, because you don’t want to be overtaken, but this has all led to a stifling of the technology and people making wild claims. Joshua is clear that any claims need to be backed up with data and currently there are no standards for how we measure and create these things. Joshua thinks that for this technology to move forward governments need to subsidise it and universities need to continue the research. It needs targeted attention and standardisation of methods, but none of this is going to happen without funding. Joshua believes the capabilities for mycelium composites are endless, as endless as the kingdom of fungi.
The mycelium-based composites are grown in the lab
Joshua explains that you need at least a food grade level of facility to grow the fungal starter culture, very different to a standard sawmill making SIPs. But one of the amazing things about this technology is you can start from a single fungal spore and grow enough material in about 90 days for several houses. During the process, the spore starts in a petri dish, and you grow it, adding a bit of material at a time. You can increase the amount of material you add as it builds up, whilst making sure the fungus isn’t getting too old, because its life cycle can be rapid. Joshua grows the material in the open air and doesn’t use rigid moulds. A remarkable part of the process is that it takes five days to grow, whether it’s one metre or ten metres, it’s the same amount of time. During that time, it fully colonises the substrate and forms a fungal skin around the outside of the material, which is tough and durable. At the end of the process, you dry it, to kill the fungus, as you don’t want the fungus to continue to digest the material. It is the drying process that gives it the rigidity and strength.
The Hy-Fi tower
Experimental projects demonstrate potential for the future
Joshua completed a non-structural project in New York City two years ago using their mycelium-based composites. The second half of that project was to include the manufacturing of chairs, but difficulties in finding the right facilities to dry the material brought things to a halt. The Hy-Fi tower at PS1 in New York City is a well known example of using mycelium bricks in a large structure. However, the tower was built of timber and the bricks are just infill. A man in Ohio has used edible mushroom mycelium blocks, compressed at a 20:1 ratio to make strong materials. Joshua is trying to develop a different process, which tests how far the fungus can go itself, so not using any industrial compression to bring strength. He is also currently limited in the size he can make, at 3m long by 300mm wide.
Okom wrks labs could also look at creating a two by four wood replacement product but at this stage it would not be as strong as wood. However, they are finding that if they grow several parts together, at the same time and cross layer them, they can build an incredibly strong 2 feet by 2 feet SIP wall section. In their trial seven parts were all adhered together by the mycelium itself. There was no glue involved and although they didn’t get to do a compression test it did seem like there was a synergistic effect by growing them together in this way. There are more collaborations brewing and the potential for space technologies for drying that would make it possible for them to restart building SIP wall sections.
Working at full scale they could compete with standard SIP wall panels
Very early on Chris Magwood suggested concentrating on structural insulated panels (SIPs) and Joshua believes that if they could work at full scale, they could produce mycelium-based composite SIPs at a competitive price. Over time, they could make that difference even greater.
Mycelium-based composites are already being used outside construction
Mogu in Italy has been creating decorative sound attenuating wall panels for a long time now, which has kept the material in the zeitgeist. There have been several attempts at creating businesses with foam packaging, but it’s been rather difficult to commercialise the products overall. Le Corbusier regarded chairs as small pieces of architecture and as Joshua is also infatuated with chair design, he thinks a fully mycelium-based composite chair could be the way to show people what is possible. It would show the industry that it can be done commercially, and consumers that you can put these things in your house. They’re not going to grow weird things off the sides, and they will have some heirloom quality to them!
It is healthy for people with allergies to mushrooms
In Joshua’s process the fungus is killed at a certain point and never reaches the fruiting body stage, which means spores are not produced. It’s usually the spores that people have sensitivities to, so it’s therefore completely healthy. The other issue is that most mycelium-based composites are incredibly hygroscopic, which means they will take up a lot of water. Other moulds or anything else, could start to colonise the material in a wet state, so you need to be able to stave off that moisture. This would be about protecting it from the elements, like you do with timber, so you would then have a system with longevity. Joshua admits its early days and hypothetical, but from his own research he thinks it is doable, and it is safe.
He explains that whilst foam-like mycelium-based composites typically have a water uptake of 200 to 300%, their material is far more dense, with a water uptake of around 25 to 45%. That’s a big leap in the right direction with more improvements possible through improving the fungal skin or adding natural products like beeswax. His goal is to avoid any kind of petroleum based products, if possible, but has accepted that using an epoxy resin covering may be a good way to get things started.
Hemp is the Joshua’s preferred substrate for growing the mycelium
Joshua is developing a composite material, which we might compare to the first earth bricks that included straw to add strength to the mud. He is using hemp as the substrate for the mycelium to grow on as it is a strong material and is “tasty” to the fungus they’re using. The fungus serves as an adhesive that binds everything together, so you’re using these two different materials to create something like a brick. He then adds in the textile reinforcement phase that provides even more strength and improves the compressive strength by orders of magnitude over the foam-like materials and other types of mycelium-based composites. That textile reinforcement phase is notoriously difficult as it needs to be clean enough to grow without it getting contaminated before the end of the grow process.
We need to re-imagine how we use materials
Even though Joshua’s data is showing increased strength in the material it is still only just over one megapascal in compressive strength. This is not great from an engineer’s perspective, so can we think differently about how we build? He is thinking about modular building rather than lots of concrete and brute strength. Instead use geometry and genius engineering to build lighter, stronger structures. Anything that makes steel lighter and stronger from a geometry standpoint, would also work with their material. There is also work to optimise the way that the fungus grows and possibly some genetic changes to the fungus that would enhance certain qualities. Machine learning can help with this process as there are so many variables to consider. People are now starting of pool resources, with Phil Ross, setting up a nonprofit, called Open Fung. This is to create baselines for researchers, so people are not starting from scratch each time and can hopefully go further and faster on the engineering side.
The potential applications are as diverse as the kingdom of fungi
Joshua believes that the potential applications for mycelium-based composites are as diverse as the kingdom of fungi, but the material needs to match the job it’s meant to do whether that’s in industrial design or architecture. It’s also important not to oversell the capabilities. Whilst patenting is important to gain investment, there is a need for more collaboration in the field, and that is Joshua’s request to the mycologists and engineers currently exploring these ideas.
“I think the future is wide open as we are at the nascent stages of understanding how fungal mycelium-based composites come together.”
Award-winning architect Kirsty Maguire shares her experience of designing and building her own Passivhaus on a challenging sloping site in Newport-on-Tay, Scotland.
Interview with Kirsty Maguire
Kirsty Maguire runs an architectural practice and consultancy in Scotland, that blends good design with environmental responsibility, to create buildings that people love. One of her clients used the phrase ‘dream catching’ to describe the process of working with Kirsty, who helps people explore what’s important to them and then turns their dreams into reality. Kirsty does this on all her projects, including her own and feels that building a house can be an enjoyable process. She remembers as an architectural student wanting to create a space for herself, to be part of that world and have that experience. It took over 20 years for her to pinpoint where she wanted to live, find a suitable plot and have the funds available to put this into practice. Here she shares her journey and experience of building her own home.
Accessing a number of plot opportunities is part of the process
The idea of building her own home was there in the background for a long time before she really started looking at sites. Her grandmother’s garden, which had an outbuilding that could be replaced, was her first serious consideration, but the timing was not right for her to do the project. However, the thought process she went through, developing her ideas there, became a stepping stone in the right direction.
When Kirsty is working with clients who don’t already have land, she will help them look at different plots to clarify what they want, what they need and what’s most important to them. Thinking about the future is also important, we don’t know what the future will bring, so having some flexibility is ideal.
Get to know what your plot priorities are
As time went by, Kirsty set up her own practice, went on some adventures, and then got a bit more serious about plot hunting. Some plots came up in Newport-on-Tay, where she was living, but although she visited them and did sketches none of them really floated her boat. But she could identify what was important to her in this location; she had to be able to take advantage of the stunning views, be able to walk to the shops, be part of a community where she didn’t have to drive everywhere. Other people will have different priorities in their plot finding, so it’s knowing what’s right for them.
Eventually Kirsty saw an advert for the plot where she now lives when she was travelling on a 10-month sabbatical. When she came back, she realised it was a great spot, a really challenging site, steeply sloping, north facing site, amazing views, but it turned out someone else had bought it. She was disappointed, which was really telling, but it came back on the market and she managed to buy the plot.
A site with a lot of constraints can become a positive
Kirsty describes it as a tricky site with strict planning restrictions, which limited the overall size of the house, the direction of the build, number of bedrooms and amount of parking. There was also an existing planning consent for a dreadful building all of which put other people off the site and worked in her favour.
It was a garden when she purchased it, but Kirsty believes it was always seen as a building plot, with the house next door maybe having bought two plots, but never getting round to building on this one.
The main challenge was the topography, as it’s a narrow site on an extremely steep slope. There is a three-storey level difference between the front and the back of the house. Properties on either side restricted the placement of windows and she needed to ensure the right to light as well as making sure she wasn’t overlooking the other properties. From a Passivhaus point of view, it’s north facing, which is a challenge and most of the views are to the north.
In Kirsty’s experience once a site has planning permission it is much easier to adjust the details of the building, if you keep within the parameters of the local plan. Kirsty took all the restrictions that had been imposed on the site along with the physical nature of the site itself and used them creatively to create the shape of the house.
A lot of the core decisions fell into place
Kirsty knew she wanted it to be a Passivhaus using eco materials, so from that point of view, some of the design decisions were already made. As timber frame building is traditional in Scotland, this was also an obvious route.
‘Upside down’ living is a good fit for a sloping site
Kirsty describes her home as an upside-down building, with an open plan, living, dining, kitchen area upstairs. This has a partial separating wall with holes in it, so that you can sit at the dining table in the south facing sunshine next to the garden and also see the views all the way to Dundee. It’s a two storey, rectangular box with a pitched roof, but the ridge of the roof runs front to back, which is the opposite direction to what you might expect. There is then a box on the side, to accommodate the stairs, bathroom and utility. From the street you see the gable end of the building, with the ground floor of the building already a storey up above the street, and then it’s two storeys up above that to the ridge. The living space is a tall, generous space, where you could potentially add a mezzanine, but Kirsty doesn’t need any more space.
Thinking about privacy is also part of the window design
Kirsty knew that she wanted a big window to the north to enjoy the views and some rooflights to get east and west sunlight into the building to make sure it was light and bright. But, as well as ensuring that she wouldn’t be overlooking other people, she didn’t want them to be overlooking her. She therefore did lots of sight line analysis, which resulted in the big picture window in the living room being raised by 400mm. Architecturally, you might have put in a floor to ceiling window, but having the raised cill gives a huge amount of privacy. People walking along the street, or even in the house opposite, can’t see in and likewise, when Kirsty is sitting on her sofa, she can’t see out.
Talk to your neighbours to get their support
Kirsty went round to her neighbours to make sure they knew what was happening and that resulted in lots of letters of support for the building. It’s important to acknowledge that you will be changing people’s local area and most of us don’t like change. If we feel included in the process, we tend to be more comfortable with it.
The people opposite had built their own house and Kirsty’s house was going to slightly reduce their access to sunlight because of the steep slope, but they were positive because she had thought of them and worked out how to minimise the impact on them. She also feels lucky because the people around her are really friendly.
Variety in the neighbourhood is often a good sign for a self build
Kirsty thought a lot about how the cladding of the building would fit into her neighbourhood. There is an eclectic mix, with Victorian buildings, a 1990s period piece opposite, a small brown bungalow next door and some lovely new builds in the village. So she ended up incorporating motifs from some of the buildings around, the big picture window is echoed in the building next door and some of the Victorian buildings across the street, as is the relationship, with the pitched gable roof.
Some features of the house were not optimal for achieving Passivhaus
Kirsty explains that some of the constraints led to architectural features that are not optimal in terms of Passivhaus. For example, there are rooflights because she couldn’t have many windows in the walls along the length of the building. Also the desire for a big open space with a cathedral ceiling creates extra volume to heat. All this means is that the insulation must be slightly thicker to compensate.
The form factor is around four, which is similar to many of the detached buildings that Kirtsy works on. For the Passivhaus certification Kirsty used heat load rather than heat demand. The heat demand is calculated at around 20 kilowatt hours/m² per annum, whereas the heat load is 10 kilowatt hours/m². Her actual energy use is more like 13 kilowatt hours/m² per annum for heat demand, which is a lot lower than the PHPP had suggested. One reason for this might be that Kirsty prefers setting the temperature a little lower in winter at 19 Celsius rather than 20 Celsius.
The size of the windows matters
Kirsty stresses the importance of getting your windows the right size, both in terms of heat loss and overheating. It might have been tempting to open the whole south gable end to glass, but she knows she would have cooked in the summer. She still has one large feature window and several other generous sized windows, and says the PHPP process really helps to show where there might be a problem and how to adjust things accordingly. Even though it’s looking at averages and could be regarded as a crude tool it did allow her to model her overheating risk to 0%.
Skylights can be tricky to shade
Kirsty included skylights as replacements for vertical windows along some of her walls and explains that you will lose more heat in winter through a window directly facing the sky and it will be harder to shade in summer. She doesn’t feel she has enough of them to cause a problem and one benefit is that they work extremely well for stack ventilation.
Strathclyde University have been monitoring the performance of the house and office for the last 18 months and both of them are working really well.
Finding time to work on the project was challenging
Kirsty is building houses all the time, so from that point of view, building her own was quite straightforward. She knows good consultants who are part of her normal work team that she could bring into the project. The hardest thing was setting aside enough time, because she was having to do all this in her own time. At least she was passionate about it, but remembers finishing some drawings whilst on holiday with friends!
Be prepared for a lot of digging out on a steeply sloping site
The groundworks phase started with digging out a lot of material from the site due to the steep slope. There was also a 2.5m high wall along the street edge that had to be taken down and soil removed to make it level with the street to create the parking area and the site for the new office. Kirsty was able to reuse the wall to create the gabions needed on site and collected more stone from other building projects around the village. And her dad even carved her house number onto a piece of stone, which was built into the new wall.
The house is on an Isoquick raft foundation, with the area around it built up with a concrete block retaining wall, which is insulated on the outside with XPS insulation. There is also a tanking layer to keep the water out, which so far has been working well. Around a third of the building sits below ground. The timber frame is filled with wood fibre insulation with a wood fibre “tea cosy” all the way around the outside including the roof to avoid thermal bridges. Kirsty often uses this technique, particularly when doing a stick build on site. She explains that there used to be few timber kits of Passivhaus quality that were manufactured off-site but now there are some good ones, including Eden Insulation that was used at The Seed.
Find out more about Eden Insulation in our training session with Stephen Gurney in The Hub.
The steep slope also meant it was harder to bring materials to site
Everything had to be carried up the steep slope, most of it by hand. Only the large windows and ridge beam were brought in by mechanical means. Kirsty says it’s also worth checking the largest size of window that can be carried on a normal truck, so you don’t have to cover the cost of non-standard transport.
It’s about choosing where you spend your money to make the best impact
Upstairs, there is lots of volume due the cathedral ceiling and this gives it a light and airy feel. There is oak flooring throughout the house with quite simple detailing and lots of plants adding interest. A local craftsman, Imric made some beautiful shelving and built in cupboards, with bespoke worktops coming from another craftsman in Edinburgh. However these items sit alongside an IKEA kitchen, Howdens flooring and bog-standard skirtings, architraves and doors.
Kirsty tells us that people often comment on a yellow globe light that can be seen from the street, which cost £20, whereas other handmade more expensive light fittings go unnoticed. She also made light fittings herself using coloured cable and used a number of long drop cables to separate spaces. It’s not just about putting up walls up to separate spaces, there are more subtle ways of dividing spaces that create layering and different views.
If you have a dream explore it with an architect
Rather than always wondering “what if”, Kirsty’s advice is to find an architect to help you to explore your dream building. It doesn’t mean you are committed to the project at that stage, but it’s good to put all your ideas on the table, sift through them and see where it takes you. You’ll probably end up prioritising them, but later you might find a way to return to these ideas that were less of a priority at the start. Kirsty loves going through this process with clients, even when they don’t know how to articulate what they want, because there are so many opportunities. She finds getting to know her clients and creating that relationship with people a really special part of being an architect. She sees private clients as really invested in the process, with many of them bringing so much of their own creativity to the conversation.
Passivhaus delivers a healthy and comfortable internal space
Kirsty sells this level of comfort to her clients and visits them in their houses but still thinks it’s difficult to understand how great it is until you’ve lived in it yourself. She was living in a small, 200 year old flat before building this house, which had all the pros and cons of an old building, but is mostly cold and slightly draughty! Much as she liked being there, she can’t really express how comfortable she is now and how nice it is to have constant fresh air.
When designing the building, Kirsty layered up so many interactions between the spaces, some subtle and some not, to capture different views. She finds it hard to pick out one thing as a favourite, but it’s probably the views through the building, being able to sit in the living room and look out all the way across the Tay Estuary to the mountains.
Sally Godber, a Director at WARM consultancy explains why reducing the risks on her own Passivhaus project was so important, what that entailed and how it enabled her to deliver a healthy, comfortable and energy-efficient home on budget.
Interview with Sally Godber
Sally is a Chartered Mechanical Engineer and Passivhaus certifier who co-founded WARM consultancy with her father Peter Warm. She grew up with her dad building different houses, always experimenting with designs and construction systems to improve energy efficiency. It was never her intention to work in this field but somehow it had seeped in by osmosis, and after university and her growing awareness of the climate crisis she wanted to work in sustainability. With her engineering background she had gone into building service design, but it wasn’t rounded enough for her as it only dealt with a small part of the building process. Combining her experience from the commercial sector with her dad’s hands on practical experience and knowledge of domestic builds resulted in WARM energy consultancy. Their services include Passivhaus consultancy and certification, focusing mainly on commercial building projects. They also offer training through their sister organisation, Coaction.
The juxtaposition of her work and her home situation became too much
The driver for taking on a project came after living in a large, damp, Victorian house, whilst working on Passivhaus projects for other people. Initially Sally and her husband Mikey had started looking for a new home, but they found themselves wanting to change everything other people had done, which felt pointless. Either they needed to find somewhere that required a lot of renovation or to start from scratch.
Managing risk became an integral part of taking on a project
For Sally the prospect of taking on a new build or retrofit was exciting, but her husband Mikey was not so sure. So when they sat down at the beginning to discuss their priorities, risk came up. For Mikey, above anything else he did not want to be crippled financially by chasing the self build dream. Luckily a large part of Sally’s professional life is spent de-risking projects and also having had ‘the big house’ experience she was after the polar opposite.
Scaling down a project scales down costs
With a tight budget one of the most important decisions you’ll ever make is setting the size of the project. If you make it too big then it will be impossible to get the quality you desire. Sally and Mikey wanted to build to Passivhaus standard, but beyond that they just wanted a modest sized, warm and comfortable family home.
“We had a young family, I had my business going on, and my husband was not totally sold into this. We really needed something that was going to be low risk. So all of the design work that we did was about being able to manage the budget.”
Risks can often be identified
Sally outlines multiple risks and how many of them can be reduced through good design. She explains that some risks start with our expectation about how a project is going to go and then the reality of what actually happens. We might be faced with cost increases or there might be a failure during construction, for example, through something not being protected on site, which results in water damage. In terms of the energy performance, the airtightness, the insulation continuity and the build quality are key. Sally sees projects go wrong when the contractor is not clear about the expectation for the build, or the design contains many complex details, which have been hard to price in advance. Although it’s a quantity surveyor’s job to cost up projects, when the design is complicated it’s much harder to work out accurately the time and effort needed to complete the build to a decent quality. So, the difference between the client’s expectation and reality could be quite significant.
Reducing the number of ‘unknowns’ reduces the overall risk
Sally will always look to pay a fair price for building work which has got the least of number of unknowns within it. She explains that it is impossible to take some guesswork out of retrofit projects because you can’t know what you are going to find. Likewise, there are always some unknowns around groundworks, but for a new build, once you are out the ground, the risks come from the things that you’ve added into the design.
Complexity increases risk
This means that the amount of risk you have on your project is down to how complex you’ve made the design. These risks can come from the geometry of the building or the construction choices. Sally explains that making good decisions during the design process may not save you money on paper, but reduce the risks of you having to build to a poorer quality and it not being what you wanted.
“The amount of risk that you have on your project is about how complex you’ve made the design.”
Know your absolute price when buying at auction
Sally and Mikey considered a few plots and existing dwellings, before spotting a dilapidated pub at auction. Key opportunities included it being in a great location in Plymouth, which was at the entrance to the historic naval victualling yard and near to the WARM office, and having a sizeable garden with a beautiful old Holm oak tree in it. So they decided to bid for it.
A top tip that Sally received from a friend is to work out your absolute maximum offer in advance of attending the auction and then not to go above it! While this may seem basic advice, as a novice it’s easy to get swept along in the moment.
Sally also gets the feeling that most people at auctions are professionals, who are representing investors, so you will be competing in this arena. However, overall she thought it was a great way to buy a building, particularly because it’s so quick. Their last bid was their absolute maximum, so the adrenaline levels were high but they secured the property.
Living in the pub gave them a better understanding of the work that was needed
The pub had a flat upstairs, so they decided to live in it for a year to help get an idea of the space and make sure they understood what the retrofit required. They quickly realised that the pub was more dilapidated than they had thought, it wasn’t well connected to the garden and the refurbishment would cost a lot more than they were planning to spend. So they explored another option instead, which was to build a new home in the garden and then refurbish the pub at a later date.
Achieving planning permission was an emotional roller coaster
Sally has a lot of empathy for people who have been through the planning process or are going through it, as it was a real headache. It didn’t seem to matter that they wanted to build a good quality, high performance building that would fit into the local environment and last for generations. It felt like a lottery, particularly when they’d had a positive response to their pre-application, only to be turned down on their full application. Luckily their architect Jae Cotterell got involved and was able to present a good case for why it should be granted, and the planning department eventually saw sense and gave it the green light.
Working with one company for the design and build was part of their original de-risking strategy
Sally tells us that part of their de-risking strategy was to get Passivhaus Homes involved. Not only did they supply a kit that was tried and tested, and would easily reach the Passivhaus standard, but at the time they were also doing the construction work. So keeping the design and build with one company was a way to get cost certainty.
With her second child on the way, however, Sally was keen to get moving as soon as possible. Unfortunately the time frame for Passivhaus Homes to carry out construction didn’t work out, so they considered another option.
Their simple design made it easier to engage with another timber framing company
The positive side of all the work they had carried out in the design stage to de-risk the build meant they could approach a more standard timber framing company.
A simple design reduces the risks during construction
The house has a simple rectangular form with a pitched roof. On one side there’s a single storey element with a flat roof to provide a view for their neighbours. This added some complexity to the detailing and being close to their neighbours also meant they had to lower the eaves on one side of the roof.
The floor area internally is 120m² and it was a priority for Sally to make this space work hard. Downstairs is an open plan living room and kitchen, which has been designed so that a wall could be added later if they ever want to separate the rooms. There is also a spare bedroom downstairs, along with a utility room and a downstairs bathroom. Upstairs, there are three bedrooms and one bathroom.
The emphasis was on making the spaces work, with Jae encouraging them not to scrimp everywhere! For example, creating a welcoming and spacious hallway was something they didn’t appreciate at first, it felt like a waste of space, but over time they have realised how valuable this is.
There were challenges using a standard timber frame
Sally explains that Passivhaus Homes use a portal timber frame, which doesn’t require a ridge beam and allows you to create spans without any supporting beams. Unfortunately, standard timber frame manufacturers are not used to doing the lift of the ground floor and first floor in one which is what you do with a portal frame. Separating it into a ground floor timber frame and a first floor timber frame meant that they needed steel beams to provide support. Sally hadn’t wanted to use steel as a material in the build and this then created some difficult detailing for the airtightness. This is where the standard timber frame suppliers really struggled and if it hadn’t been so late in the design process Sally would have changed the design to break up the spans, so they could still have used timber. She feels it’s really important for designers to understand the natural limitations of different materials rather than relying on engineers having to solve problems because you’ve created a span that’s too wide.
Allwood Timber supplied the twin stud frame, which was then filled with Warmcel insulation. They have insulation under the slab and the roof is treated the same way as the walls, with blown-in cellulose. The structure is I beams, with OSB board on the inside.
Another advantage of a simple design is that you can run your eye over everything to see it’s all in order, such as making sure the airtightness line is continuous.
Remedial work enabled them to achieve the airtightness target
They did some of the taping themselves, along with the timber framer and after a poor first air test (1.2 air changes per hour at 50 Pascals) they realised they hadn’t pressed down the tapes enough. As soon as they did this and activated the glues, they saved another 0.2 on their air test. There was also air leakage around the steel beam. If she’d done the project today Sally would have used an airtightness paint to sort this out, but back then she had to spend a late night putting a lot of tape on it. Their final air test achieved 0.56 which meets the Passivhaus standard performance criteria.
Their windows and doors are from Rationel, because Sally had used them before and knew they were relatively cheap in comparison to others. They also designed all the windows so that they could be openable with a single span, with a lot of them being top hung so they could leave them open at nighttime. They’re a simple design with easy detailing, which all helped during construction. Sally feels it was still hard to achieve good airtightness when they didn’t have a lot of time themselves to check things and weren’t working with people with experience of this type of build.
They achieved a better airtightness with the pub retrofit a few years later, working with a local contractor called Greenacre Design and Build who had an amazingly skilled team. They were great problem solvers and fantastic at detailing, so they did exceptionally well even though it was their first time doing a Passivhaus retrofit project. But sometimes you don’t have those teams, and so being able to keep the details simple is really helpful.
Sally took over managing the build as soon as it was watertight
Sally made the decision to take over the project once the building was watertight. This meant they could project manage, be in control of the individual contractors and communicate directly with them. For example they got a contractor in to do the plastering and did all the services themselves, apart from the final electrical bits. They brought in a friend, a carpenter, to do the internal finishes and he refused to use soft wood! This really put quality into the build and is now much appreciated by Sally and her husband. It did take longer to complete the build as they were quite restricted with the time they could make noise in the evenings and at weekends, but it was good to feel more in control.
“We found that once it’s watertight, it feels like you can just breathe a bit, and it’s a bit easier to manage.”
It’s worth taking the time to get things right
It took two years from the point where they bought the pub to them being able to start construction and one year to do the build. The first year was deciding what they wanted, going from the pub renovation to a new build, then another year designing and getting planning permission. At the time all the faffing felt frustrating, but seven years on she can see that it was worthwhile and meant they ended up with a better home that will last them much longer as a family.
Sally had also learnt from her parents’ projects that it’s best not to move in until the house is finished as the work just doesn’t get done after that. One of the things they hadn’t done was tile the kitchen, which was only done six years later!
The house was delivered on budget, but the time put in hasn’t been calculated
It was a real success for them to deliver the project on budget, but with a self-build the amount of time put in is huge and something Sally doesn’t want to calculate.
There were some complications during the build, not necessarily associated with the design and things that they would definitely do better next time. They were very careful and conservative to achieve their budget and there are some things they might want to be different. Luckily noticing the faults wears off with time and over the whole project there is just one window that Sally wishes was larger. She was worried during the build that they were being too careful and maybe the building would feel mean, but it doesn’t.
“If you are on a tight budget, it makes a huge amount of difference feeling in control and that was ultimately why we took on the self-build.”
Managing the contractors themselves meant there was no middleman, they could negotiate individual prices and have conversations about the materials they were using.
Sally describes herself as a Passivhaus geek, but even so there was so much she didn’t know. This has given her a huge appreciation of all the different skills needed in a team to complete a build project.
She tells us how she really enjoyed the whole experience, both stretching her mind and also physically doing stuff. She doesn’t think there’s enough of that crossover, with designers getting practical hands-on experience. With the pub finished three years ago she’s definitely ready for another project but has nothing particular in mind.
Sally got to appreciate Passivhaus certification from a client’s perspective
They had designed the house to Passivhaus standard but hadn’t discussed certification until they were just about to start the build. Sally tells us that at the time she was absolutely exhausted and didn’t think she had the energy for it; it would be just too much hassle. Her dad, who doesn’t often tell her what to do was very clear that not doing it wasn’t an option, particularly considering her job!
They employed Will South of Etude to do the certification so that they had someone independent looking at the project. In the end, the certification process proved incredibly valuable for Sally as she knew there was a second pair of eyes checking on the project details. She was doing her best to check things but was incredibly busy and Will picked up on a few things that were wrong. Will had identified that they’d got their shading wrong, which they were able to correct, but it was too late to change the insulation, which was not the right specification. They had enough margin in the calculations for this not to matter, but by identifying it early they could have made adjustments elsewhere if they’d needed to.
It also gave Sally a real appreciation of just how hard it is as a client getting everything together for certification and the need to find the right level of checking. She is still a massive advocate for certification and as there’s very little quality control it’s good to have someone whose sole job is to check that you’ve built what you said you were going to build.
Sally’s husband is now an advocate of Passivhaus!
Sally says her husband wasn’t totally onboard with MVHR, triple glazing or even achieving the Passivhaus standard, but she was clear that these things would be worth it. They’d moved from a large Victorian house that was uncomfortable and difficult to manage into a tiny pub flat where she was cleaning mould off the walls. The flat was just 60m² and inevitably there were arguments and conflict. So, the experience of moving into somewhere that was a lot bigger was obviously like a revolution for the family. Sally tells us that it was so warm in the house that the kids wouldn’t believe they needed to put on coats to go outside. She had been spouting the theory to everyone, but it was still amazing to experience the comfort and warmth for herself. Her husband was quickly converted to this way of living. They also realised how they’d stopped inviting people round to the pub flat because it was so damp and at the time Sally hadn’t realised just how much inherent stress the mould and the dampness were giving her. She admits to being a total snowflake now, finding it very difficult to stay in other people’s houses.
Try to enjoy the whole house-building journey
In hindsight Sally reflects on the self build journey as a really lovely process, but this is not always how it feels at the time. She gives an analogy of when you have young kids you can feel like your hair is on fire, you’ve got sick down your front, and you’ve just stepped in something you’d rather not have. But when you look back, you think that was an absolutely incredible experience. She says to find ways to bring your family together through the process and the same with your wider building team. The relationship side of a building project is really important. So, as much as possible try to enjoy the sick down the front feeling!
