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.”
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.
Florence Collier, founder of Humblebee, takes us step-by-step through the deep retrofit of her 1970s home. She explains the costs relating to each measure and the cumulative total as the project advances.
Interview with Florence Collier
Florence Collier, founder and owner of Humblebee is a chartered mechanical engineer and Passivhaus Designer. A large part of Humblebee’s work is around home retrofits, both modelling and carrying out retrofit assessments. Here Florence takes us through the retrofit of her 1970s house, giving us costs for each part of the project, talking through her decisions and showing us how the different aspects of the work fit together.
Front of house (before the retrofit work)
Reducing carbon emissions was the driver of the project
For Florence reducing carbon emissions was at the forefront of what she wanted to do, but she also had a desire for more community-based living. Cohousing would have been ideal, but she was aware of how much work and time goes into getting a scheme off the ground. When a property came up with a simple footprint, in a good location, that was in need of updating, she thought this was a perfect opportunity to retrofit to the EnerPHit standard, and put into practice everything she had learnt from the Passivhaus training course.
Back of house (before retrofit work)
The simple shape of the building made the retrofit easier
The house was a typical 1970s cavity wall brick construction with a ventilated suspended timber floor. Florence explains that it was basically a box, with a plastic portico stuck on at the front and a single glazed, brick porch at the back. It was clear that to do a proper retrofit both of these structures would need to be removed.
If you have skills and time, you can save money
As a professional in this field Florence was able to model the whole building, make decisions on materials and commission each piece of work as required. She did work with an architect on a few of the details and would advise anyone who doesn’t work in this industry to get a specialist on board to guide you through the process. The material and labour cost of the retrofit to date is just under £106,000, which doesn’t include Florence’s time and other items that could add an extra 10-15% to the total cost.
The plans for the project
All decisions tried to balance efficiency and embodied carbon
The plan was to get as close as possible to the EnerPHit standard, which is the Passivhaus standard for retrofit. This essentially targets a space heating demand of 25 kilowatt hours per square metre per year. Florence knew they couldn’t reduce the embodied carbon already in the building, but they could keep any new features as low carbon as possible and reduce the operational carbon. Moving off fossil fuels was the goal alongside creating a healthy home, free of mould and condensation and with fresh filtered air.
The first step is to get over any mental blocks that you’re having to starting this journey, because it’s so easy to say, well, I can’t do this unless I’ve done this.
Florence took on this step herself
Loft insulation was a small but important first step
When Florence found herself stuck at home during lockdown, it seemed like the ideal opportunity to get started. So they ordered in the materials for the loft insulation and then installed it themselves. Florence explains that although the loft insulation was less than 3% of the total retrofit cost it was an important first step, as between 8 – 10% of their heat loss was through the roof. They chose to use wood fibre and hemp, which aren’t the cheapest insulation products, but sustainable and nice materials to work with. Check out Florence’s blog to go into more detail about this step.
Material costs for loft insulation £2,700 for 56.5m²
The cavity wall was filled with EPS beads
Cavity wall insulation can be added independently of other retrofit works
Whilst waiting for other larger works to begin Florence was able to go ahead with the cavity wall insulation as it didn’t depend on other aspects of the retrofit. She found it was a straightforward step in terms of the material choice, not choosing a natural material in this instance because of the risk of drawing moisture from the ground. In a cavity wall, the cavity is there to conduct any trapped moisture away from the internal walls, so your insulation needs to be moisture repellent. They used EPS polystyrene beads, which have a decent thermal conductivity and contain some adhesive so the beads won’t pour out of your wall if you make a hole in the brickwork. Again, this was a relatively cheap step to take, and the effect was noticeable that winter. Check out Florence’s blog to go into more detail about this step.
Total cost of materials and installation £1,701 (approx. £15.50/ m²)
The new triple-glazed windows go in
Next came the replacement of the old PVC framed windows
The house had double glazed PVC framed windows that were coming to the end of their life. Florence wanted to avoid using plastic in their replacement and opted for timber windows instead, which also looked good aesthetically. They chose triple-glazed windows from 21 Degrees, but from their slightly cheaper range that were not Passivhaus certified. From the PHPP model these windows would still allow them to achieve their energy targets. An external powder coat finish on the windows extended their warranty and protects them from the weather.
Florence explains that a lot of the heat loss through windows is through the frame, so they simplified the number of panes and openable parts. Fixed windows have narrower frames, so it’s about trying to find the right balance between fixed and openable. Having fewer openable windows also helps with airtightness.
The windows sit in a plywood box
Florence was aware that installing their new windows was always going to be a challenge, as they needed to ensure both airtightness and insulation continuity to avoid thermal bridging. Installation ended up taking a day per room, with a plywood box built and fitted to each window before then lifting all of it into place. This was needed to bring the plane of the window in line with the planned external wall insulation. The box allowed the window to be pushed out into that layer, which could then be taped and sealed for airtightness. Check out Florence’s blog to go into more detail about this step.
Total cost of windows and installation £22,033
Florence putting on some external wall insulation
External insulation is like wrapping your house in a blanket
Florence explains that heat gets conducted out of your house wherever there is a junction or fixing structure that is not made of an insulating material. Wrapping the house in external wall insulation (EWI) is therefore an easier approach compared to trying to insulate internally. Florence chose wood fibre as a natural material with low embodied carbon, which would also be good to work with from a general health perspective. The brick construction of the existing house was built to be vapour permeable and wood fibre would maintain this breathability. A lime render was used on most of the house to create a weatherproof layer, with some timber cladding on the ground floor frontage to provide variety and break up the box shape.
Where the walls meet the floor can also create a thermal bridging issue, so Florence wanted to continue the wall insulation down to the sub floor. Wood fibre was used from the damp-proof course upwards and then below that they used a polystyrene plinth, that could be wrapped all the way round. A French drain type system with gravel was used to channel any water away from the building itself. Check out Florence’s blog to go into more detail about this step.
Total cost of materials and installation £26,100
The MVHR unit is in the cold loft
The siting of the MVHR unit was not ideal
Florence explains that she designed everything in parallel, making sure she could see the route for the ductwork before choosing windows. They were clear from the start that the MVHR unit would need to go into the loft. This means the main ducts are running from the unit along the loft floor into a couple of rises, with branches off to minimise the amount of distribution within the house itself. They have a couple of bulkheads dotted around and one or two ducts on display as a bit of a talking point. As they don’t have particularly high ceilings they weren’t going to lower any ceilings to accommodate the ducts and also didn’t want to go through floor joists on the first floor.
In general Florence would not advise putting the MVHR in the loft, particularly if it is a cold loft. It’s fine if you’ve insulated at rafter level, but if you’re trying to hit targets like EnerPHit, all heat loss counts and the amount of ductwork outside the thermal envelope, even insulated does contribute to the overall efficiency of the MVHR. They tried to minimise this by insulating all the ducts with 50mm foil-backed duct wrap. Check out Florence’s blog to go into more detail about this step.
Total cost of MVHR system and installation £ 9,880
Some external shading was built into the design
Shutters could be used more as a simple shading solution
Being half French, half Italian, Florence is used to shutters as a shading device. She sees them as an easy way to slash air conditioning loads in commercial buildings and to make domestic settings more comfortable. Florence was aware that her southwest facing bedrooms were going to overheat in the summer and the initial plan was for simple outward opening shutters, that you pull to and latch. Florence then realised that their windows were quite large with only a third of the window openable, so that type of shutter wouldn’t be possible. They quickly moved to the idea of sliding shutters, but it was still a challenge to find the right dimensions and the right sliders. The next issue was how to fit the solid wood frame to the external wall installation. The answer was to fit lintels above and below the windows made of a composite foam material, that would be less of a thermal bridge than timber.
The wood fibre insulation on the outside of the building has a good thermal mass so this also helps to keep the building cool in the summer. The MVHR can be put in ‘summer bypass’ mode, so when it is cooler inside than out, it can reduce the temperature of the incoming air. But the shutters have increased the comfort level and provide privacy, a sound barrier and security if you want to have the window open. Check out Florence’s blog to go into more detail about this step.
Total cost of shutters and installation £5,547
The suspended timber floor
The finished earth floor
Improving the thermal performance of their floor
Florence tells us that when she first started planning the floor there just seemed to be two options, insulate their suspended timber floor or replace it with concrete. The floor joists could be insulated with an airtight and windtight membrane but would still need to be ventilated which would compromise on the thermal efficiency. She was not keen on concrete because of the embodied carbon and saw it as a cold and hard finish. After hearing Jeffrey Hart talking about earth floors she spoke to another retrofit assessor who’d had an earth floor put in with underfloor heating. They had a deep void, so room to build up the layers needed for an earth finished floor.
They started with an insulating layer of recycled foam glass aggregate which is a lightweight, inert and hydrophobic material. This was put on a geotextile membrane to a depth of 450mm which gives you most of your insulation. Soil goes on top. Florence used MOT type one, which is compacted down to create a solid base. The earth floor finish is a clay, lime and sand mixture with added dust to give the pigment. This layer is only 20mm and is then oiled, waxed and buffed to create a smooth finish.
The original estimate was around £20,000, with most of the material cost going on the glass aggregate. However, they experienced a few delays, initially because the amount of aggregate needed had been miscalculated and so more had to be brought in. The MOT soil was then very wet, so extra time and large fans were needed to dry it. Some miscommunications over how the floor joined the interior wall led to more delays and this work had to be done retrospectively once the earth floor was finished. This all led to extra costs. Check out Florence’s blog to go into more detail about this step.
Total costs of materials and installation £30,318
Want to go in-depth on retrofit? Check out the Kinver story in The Hub.
Finally the electric hot water tank allows them to be independent of gas
Florence explains that they always planned to get off gas and had been keeping their old boiler going until they could get their new cylinder installed.
The hot water cylinder is a Mixergy tank, which Florence describes as an intelligent hot water tank. It has been installed in the loft and will have an insulated cupboard built around it. The tank heats from the top down, separating the cold from the hot, so you’ve always got an amount of hot water ready to use. It uses machine learning to heat water when needed and a PV diverter so any excess solar that is being generated goes to the immersion heater and gets stored as hot water.
Total cost hot water tank and installation £6,859
Extra heating will be from electric panel radiators when required
As the work progressed, radiators were removed from the house and once the water tank was working there was no further need for their combi boiler. The plan is to use electric panel radiators where extra heat is required. More heat may be required at the moment as the floor is still drying out. Florence also realised after a cold winter that the MVHR system hadn’t been on the right setting for full heat recovery.
Replacing plasterboard ceilings is one of the last things to do, but it’s a messy job
One key task remains which is the airtightness of the ceiling on the upper floor. Although they’ve insulated the loft, they’ve still got cracks in the plasterboard ceilings, and a leak in the condensate from the MVHR means they now have a hole in the bathroom ceiling that is just covered up with a piece of ply. They plan to take the plasterboard ceilings down, which is going to be a messy job. That will be the final stage and should reduce their heat losses to EnerPHit levels.
Are heat pumps enough or are fabric improvements needed first?
Florence says there is a lot of talk about heat pumps and whether you should do fabric improvements first or just swap your boiler out for a heat pump and be net zero ready. Florence designs heat pump systems and thinks they’re an incredible technology but feels that reducing it to either this or that option means you’re not taking into account the benefits that come from a well-executed retrofit. You might be able to get the numbers to stack up, but for Florence it is about more than just reducing the carbon emissions. A really important part of her retrofit has been about health, comfort and the general quality of life that has been achieved through the fabric improvements. Even temperatures throughout the house, no draughts, moisture or condensation and constant fresh air all add to the comfort levels. The MVHR helps asthma sufferers and allows you to dry clothes inside as the moisture is constantly being removed. Together these aspects are incredibly desireable.
Paul Testa from HEM Architects explains the difference between renovation and retrofit, using his own home as an example of a deep retrofit.
Interview with Paul Testa
Paul Testa is a director of HEM Architects in Sheffield. He’s been on the podcast before highlighting a few hidden costs you might experience on a house build project. Today he’s explaining some common terminology when it comes to altering homes: renovation, retrofit, remodel, extension and eco renovation.
While these words might seem self-explanatory they can get lumped together and we perhaps miss some of the nuances. So Paul is going to explain each term as well as share a few details from his own retrofit.
Renovation is about bringing your house back up to standard
A renovation is work that brings a house back up to a good standard. Not only will it be about making it look nice but it will deal with any disrepair, and perhaps replace the electrics and plumbing. New windows might be installed. It may also include putting in new kitchens and bathrooms, and then plastering and repainting.
Paul gives an example of buying a Victorian terrace that needs lots of work. You are renovating the house to bring it up to date and make it suitable for modern lifestyles.
Remodelling is rethinking how the spaces work
Remodelling is when you consider how the spaces work together at a more fundamental level. It’s not just about what the home looks like, but how the spaces are connected, maybe bringing multiple rooms into an open plan layout. Upstairs it may be about making better use of bathroom and bedroom spaces. It will likely involve moving internal doorways and removing walls, and whilst it could include external changes to doorways and windows this is less common.
Extensions are about creating more space
Extensions or additions are about adding more space. Sometimes a client may think they need more space but a remodel would actually solve the problem. Often extensions are needed as families grow or needs change. Paul says that it’s quite common for people to want a larger kitchen, dining space that faces onto the garden, which is very different from how houses were laid out in the past.
“We live very differently now, we congregate in our kitchens, and often remodelling can deal with that, but sometimes you do need to gain more space in that area to fully enjoy those benefits.”
Retrofit deals with performance
Retrofit is a holistic approach that improves the building fabric, making a space more comfortable, healthy and energy efficient. As part of this upgrade moisture will need to be managed and a good ventilation strategy is required.
Clients may have different drivers for carrying out this work, such as wanting consistent energy bills, so they are not so affected by energy price jumps, or increased comfort because they can’t get the house warm enough in the winter, or they may be motivated by reducing their carbon emissions.
With the right budget a retrofit can deal with all of these pain points but often work might have to be phased and the immediate solution will address the priority.
Doing work on your home locks in the performance for the coming years
While a renovation project might create a beautiful home it may not improve the performance at all and once the work is complete the homeowner is unlikely to want to make any significant changes for the foreseeable future. So this might lock in poor performance for a number of years.
The benefits of retrofit are ‘felt’ rather than seen
When a retrofit is complete it may look much the same as if renovation work had been carried out. The difference will be in how the building feels and performs.
The investment is going into modelling and understanding the initial home, developing detailed designs and then installing additional insulation and introducing an airtightness layer. High performance windows and doors will be added and ventilation will have to be addressed, often using mechanical ventilation with heat recovery (MVHR).
Paul retrofitted a 1970s semi-detached home
In 2013 Paul and his family bought a 1970s semi-detached house, which had a two storey side extension that was poorly laid out and a small sun room to the rear. The sun room was boiling in the summer and a cold store in the winter, and the main house was also freezing. This property was ripe for an intervention.
The harsh winter of 2013 was the driver to do something about it but it wasn’t until 2018 that work began. These processes take a long time and architects, much like builders, are always last in the queue.
Once the plans were formulated the main structural changes saw the original extension and old garage demolished. Although there would be a new single storey rear extension and a two storey side extension, overall there would only be 15m2 of extra space (making the floor area 136m2) when compared to the existing dwelling.
Downstairs the suspended timber floor was removed and replaced with a concrete raft. This had between 20-70cm of insulation beneath it and provided both the new floor finish and also the structure for the extension to sit on (so there was no need for separate footings).
The extension is timber frame, with 140mm deep studs, insulated with mineral wool in between and then wood fibre on the outside of the studs and rafters.
The original house was insulated internally with wood fibre insulation and careful consideration was given to the thickness of this so that moisture is managed well and the risks of interstitial condensation are minimised.
If this condensation appeared inside the construction it would damage the fabric over time and potentially produce mould spores that will end up in the air.
The roof of the original house has also been well insulated with mineral wool and wood fibre.
When it comes to the windows, Paul used a mixture or inward and outward opening triple glazed units. The reason for this was because it depended whether the insulation was internal as in the main house or external as in the extensions.
Mechanical ventilation with heat recovery (MVHR) provides constant fresh air and Paul describes this as a game-changer.
“The house always feels fresh, we don’t have any condensation anywhere, and we’re not losing that heat. I think the MVHR also helps with heat distribution, as we don’t have many heat emitters in the house. In 2018/19, when we were doing this work heat pumps were not as readily available as now, so we chose a boiler with a hot water tank. It’s the smallest system boiler we could buy, so that it can modulate down low enough for our 2 kW heat demand or heat load. This provides the hot water and runs a radiator in the living room and towel radiators in the bathroom and shower rooms.”
Paul says that in the autumn and spring they don’t have the heating on at all. The house might be at 19C initially but by the time everyone is up and moving all the incidental heat gains (from activities such as showering and cooking) warm it up to 21C or 22C.
They also have a couple of portable panel heaters (30W each) that can be moved around the house as required.
Unfortunately Paul’s house did not reach the EnerPHit standard as the final airtightness test came in slightly above the required levels at 1.08 air changes per hour at 50 Pascals. Interestingly during the build process they were on track, with readings of around 0.7 air changes per hour at 50 Pascals.
This goes to show how important it is to get the team to protect the airtightness layer once it’s in place.
The space had to work well for the family and perform brilliantly
As this conversation has been around the nuances between renovation, retrofit, remodelling and extensions, we asked Paul what his priorities were as he considered his funds.
Our budget was fantastic for a renovation and remodelling project, but once you included the retrofit elements it was much more constrained. I wasn’t really willing to compromise on performance… I was also aware that whatever we were doing to the house we were likely to be investing more than the house was really worth. So it wasn’t about getting a monetary return but getting a return in terms of comfort and health.
Although the work did put the family under financial strain at the time they don’t have a huge mortgage and now they’ve got some control over their heating bills.
They also didn’t complete everything at the time and left some DIY jobs to tick off over the years.
If you’re one of our Hub members, Paul also has a retrofit case study of Sycamore Hall.
Quality assurance is a big part of performance
If you can’t afford or don’t want to do a high performance retrofit you have to realise that there will be an impact on performance.
Paul says that if you’re adding space and extending you will need to meet building regulations which are better than they once were. The challenge is in making sure there is good workmanship on site so insulation is well installed and continuous. Moisture must also be considered and good ventilation is important.
Damp, mould and condensation are likely if you ‘just’ renovate
Just renovating an existing dwelling will not change the performance. So if there were problems with discomfort then they will still be there.
Paul has been to houses with brand new bathrooms and observed black mould around window frames. This is a sign that the moisture balance, ventilation and surface temperatures haven’t been considered.
Stripping back a building can help identify and fix problems
Quite often damp patches can stay hidden and you might not even realise you have a problem until something fails.
So major work is an opportunity to check that the home really is in good health.
National Retrofit Hub is providing a central Knowledge Hub to support all retrofitters
In terms of useful resources Paul suggests looking at the National Retrofit Hub, which aims to collaborate with those already carrying out retrofit projects, empower the next generation and facilitate retrofits in the UK.
It’s a nonprofit organisation that brings together all those involved in the retrofit sector to share their expertise and work together to enable a National Retrofit Strategy to be delivered.
It’s also teaming up with various organisations to reach architects and builders as well as those who might be considering a DIY approach.
Their goal is to see retrofit carried out at scale.
We have to start valuing health and comfort
The dial is moving slowly but we are starting to value good air quality and comfort in our homes. A few years ago internet speed was a more important factor!
Also, historically, energy has been cheap and it has been simpler to keep heating our leaky homes. However, we’ve already experienced sudden energy price hikes and this has forced people to become more aware of energy performance. Although this may not be translating into people investing large amounts to save money on heating bills it does mean they are paying more attention to energy performance and EPC certificates when buying houses.
Key challenges to consider for retrofit projects
Before you embark on a retrofit project the first thing is to make your home retrofit ready. Deal with leaky gutters, a roof in poor repair or bad pointing to make sure your home is in a good state first.
The second challenge is who to turn to for advice. You need to be sure that the advice is independent and solution agnostic. In other words you need to be careful the advice is not part of a sales pitch.
Paul mentions a few organisations and community interest companies around the UK:
Finally Paul underlines the importance of working with professionals who understand the moisture risks.
The newer the building that you’re working with, the less of a risk that is, but for example, with an old stone barn conversion you need to be aware of moisture risks. We’re now starting to see some retrofit assessors and retrofit designers who are specifically qualified in heritage buildings as well.
Andy Moger, from Tetlow King Planning, explains the role of a planning consultant and the benefits they can bring to a project.
Interview with Andy Moger
Andy is a planning consultant for Tetlow King Planning: a planning and development company based in Bristol that operates nationwide.
A number of years ago he worked on the government’s first pilot scheme for self and custom build – the Heartlands project in Cornwall. Following that, he became more involved in the self and custom build sector, primarily doing work for the Right to Build taskforce. Nowadays, this sector is all he works on, dealing with applications, appeals and site promotions, ranging from single dwellings to larger developments and appeal work for some of the big house builders and strategic land promoters.
Not all building projects will require planning approval
It is possible to use ‘permitted development’ rights for work like small extensions and loft conversions, depending on the extent of the area you’re adding to your property.
The ‘prior approval’ process typically applies to larger extensions. You inform the council who will notify your neighbours. If there haven’t been any objections after a period of time then you’re deemed to have consent.
Local plans control development in each area
Each council has to have a local plan; sometimes called a district plan or core strategy. These set out a strategic approach for that area for the next 15-20 years, and contain the policies that control development. If you’re looking to get planning permission on a particular piece of land you will need to check your local plan to see how you fit with those policies, or how you might overcome any potential issues.
All of these plans will work on the basis of concentrating the development in the most sustainable locations, which will tend to be the largest settlements within an authority area. The settlement hierarchy is:
Towns and cities
Larger villages with a broad range of services
Smaller villages that have some facilities but still place a degree of reliance on higher-order settlements
Hamlets and open countryside where the presumption generally is against development happening unless there are specific circumstances, such as for essential agriculture
Start with a site appraisal
A planning consultant can carry out a site appraisal before you get to the application submission stage. This looks at a number of areas that might be a barrier to getting planning approval:
What the local policy position is
What the chances of adhering to those policies is
Site constraints, such as flood zones, ecological designations, conservation areas, nearby heritage assets, etc
This would be followed by a number of surveys and reports
Providing that the planning consultant thinks they can demonstrate that the project complies with the local plan, a number of surveys need to be carried out to support the planning application. These will depend on the scale of the development but it is likely that some will be requested.
An ecological report will typically be required to identify whether there are any protected species on the site and sometimes these can only be carried out at a specific time of year. If you miss a survey calendar window, you may need to wait until the following year before trying again.
Additionally, a transport statement will look at visibility splays and traffic generation from your scheme. Depending on where your site is, there could also be heritage reports, ground contamination reports and archaeological investigations.
Local validation requirements will tell you what you need to submit
Local validation requirements supplement the national validation list, with what the local authority considers as appropriate for their area. It tells you what information you need to provide with your application when you submit it. Once you have submitted all the required information on the Planning Portal, and paid your fee, you wait for the council to validate it.
There are two routes to a planning decision
If there haven’t been objections to the scheme, or if they’ve been addressed and the case officer is satisfied, then there are two routes to planning approval that might be taken. The first is their delegated decision, which tends to be on smaller, non-contentious schemes. This is where the officer has been given the power to grant or refuse planning consent.
The other route is where it is put forward to a committee. This might be because it has been called in by a local councillor, or because it is more contentious with a number of objections.
You have six months to appeal a decision
If the case officer or committee refuse the application, you have six months in which to appeal. There are three routes for this.
The first is called written representations, which is the easiest and cheapest. In your statement you would set out your case and submit it to the planning inspectorate. The council does the same. The planning inspectorate reviews both statements and makes a decision as to whether the appeal should be allowed or dismissed.
The second route is a hearing. Both sides set out their case as above, but then attend a hearing together in person. The planning inspectorate will listen to both parties before making their decision.
And thirdly, it can go to a public inquiry. This is the most expensive and time-consuming and is run very much like a trial. There are barristers and witnesses, and the inspector will sit as judge. They make their decision based on the written evidence and what they’ve heard in the cross-examinations.
Choose a planning consultant based on their relevant experience
If you’re looking for a planning consultant to work on your case with you, it is sensible to choose one with relevant experience of the appeals process that you are using. They should be a member of the Royal Town Planning Institute (MRTPI) and have a good track record locally. Don’t be afraid to ask for examples of cases they’ve won, so that you know you’re going with someone who is familiar with local policy and has relationships with councillors and officers in the area.
Councils have a statutory duty to make self build land available
Putting your name on the Right to Build register means that the council has a legal duty under the Self-build and Custom Housebuilding Act to issue the same number of permissions as there are names on the register.
Andy has been involved in appeals where they have been able to argue that because the council have failed in their legal duty to issue enough consents for self and custom building, then land which might be outside of settlement limits should be permitted for development.
Andy has also found that although some councils claim to have met their obligations by granting the same number of single dwelling permissions as there are people on their register looking for a plot, further investigation shows that actually, the majority of them aren’t for self or custom build at all. Some of these can be planning permissions for up to 9 dwellings, where they’re clearly developer-led models with no ability for customisation.
Self Build and Custom Housebuilding Supply in Braintree
8 out of 10 people aren’t aware of the Right to Build Register
In one appeal that Andy worked on, although the council had met its obligations, they were able to argue that secondary data sources showed the register was actually a massive underestimation of the numbers of people in the area that wanted to self-build. Many of these were people that weren’t even aware of the self-build register. The inspector in that case allowed the appeal, even though the council had met its statutory duty.
Andy would encourage anyone to add their details to this register though, as this will increase the number of self build plots the council legally has to make available.
Outline planning permission is less risky
A full planning permission provides all the details about your scheme, including layouts, landscaping, scale and massing. If you were to then get planning consent, all you would have to do is discharge the conditions against it, such as material samples, working hours on site etc.
What a lot of people do is seek an outline consent with access only. This is an illustrative plan showing what you intend to put on the site. With outline approval you have to get subsequent reserved matters approvals for all the elements that you haven’t included at that stage. Outline permission is cheaper, so is therefore considered less of a risk.
Andy stresses the importance of discharging any pre-commencement conditions, prior to starting work on site.
Self builders can apply for CIL exemption
CIL is the Community Infrastructure Levy that some councils have implemented. It is a per square metre charge on development and is intended to pay for strategic infrastructure. Self builders can apply for an exemption, but it is incredibly important to follow the process correctly, and within the timeframes, as failure to do so could lead to a bill running into thousands of pounds.
Homeowner Guy Hargreaves reflects on adapting and expanding his Victorian mid terrace home, retrofitting the whole building to EnerPHit standard.
Interview with Guy Hargreaves
Initially we chatted with Guy Hargreaves (episode 297) about his aspirations for upgrading his period property for energy efficiency, comfort and to future-proof it for a less hospitable climate. He had gone through the design process and gained planning consent to adapt and extend the property, and targeted Passivhaus standard (largely helped by the form or shape of the building) for the project.
In this episode Guy returns after the renovation and reflects on the construction stage as well describing what the house has been like to live in.
Guy has been fantastic in sharing the journey in our membership community, The Hub.
Go behind the scenes of this deep retrofit. Get access to our in-depth video case study in The Hub
Access issues meant a lot of manual labour
The project began in February 2021 with the strip-out but initially everything had to be removed through the front door! As the one-way street was narrow construction waste had to be dealt with immediately, so it was placed into the back of a truck, driven to the builders’ yard and sorted there.
Access improved after a ‘win win’ arrangement
As time went by, Guy managed to negotiate access through a private car park at the rear (on an adjacent road). In return he offered to resurface the car park at the end of the process, fix the lights and replace the fence.
Before the renovation
Visualisation of the proposed scheme (at the rear)
New foundations were prepared for the extension
At the rear of the property a small lean-to extension was demolished and fresh foundations were dug for the new extension which would be the width of the property. A digger was craned into the garden from the car park to make the excavation work easier.
Tonnes of soil was removed to prepare for the new foundation.
Then the concrete went in, followed by a layer of insulation and a floating concrete slab.
Steels help open up the old house, but were not necessary for the retrofit
A key element of the brief was to open up the space and so a couple of walls on the ground floor had to go. Structural steels spanning the width of the house were added to take the loads from above.
Some steels already existed in the house from previous renovations but these needed to be replaced.
A contingency is always essential on a retrofit
It is impossible to predict everything that may crop up during a retrofit which is why a healthy contingency fund is always required. One ‘nasty’ on this project was the condition of the bay.
Although a homeowner’s survey was conducted when the property was purchased it did not flag up any issues. However as the building was stripped back cracks around the windows and crumbling brickwork were revealed, and it became clear that a structural engineer would have to take a closer look.
The outcome was that the bay needed to be rebuilt at ground level with some underpinning necessary at basement level.
Insulation and airtightness strategies change around the building
With a mixture of new and old, brick and timber, combined with planning constraints the technical design utilises several difficult wall build-ups. For example, at the front of the property the appearance had to be preserved and so an internal wall insulation strategy was necessary. This breathable build-up has several layers including a diathonite plaster (the airtightness layer), wood fibre board and a lime based plaster.
The ceiling height in the basement was not as generous as the floors above but removing a 75mm screed layer gave them a bit of wiggle room to add 40mm of rigid insulation.
Up in the attic room rigid insulation was used in the roof. And at the back of the house softer wool batts were filled the timber frame.
Larsen truss built on site for rear extension
The new extension is timber frame and uses a twin stud Larsen truss (300mm) to create a decent size cavity for the required insulation. Cutting and erecting it on site is a simple and cost effective route to achieve high performance.
The room at the top of the house was expanded
A previous owner had converted the loft but the sloping ceilings made it slightly awkward space so Guy planned to open it up on the garden side (south side), which also affords the best view in the house.
The skylights before the renovation
Guy understood the overheating risk of the dormer room
That whole south side we glazed in a rather aggressive and somewhat controversial scheme that is going to be a work in progress over time because that dormer is the top of the house… The heat in the house tends to rise into the dormer and add to the solar gain.
External blinds will be installed if ever needed
While over-glazing will lead to overheating Guy did not have his eyes closed. Instead he made sure that there was a strong back-up plan. So there were plenty of window ventilation options as well a reverse cycle heat pump, which can be used for cooling. However, if the temperature becomes unbearable then the ultimate solution will be external shading.
He was on site every day checking how the airtightness layer was coming together, highlighting potential weak spots.
Airtightness became a personal challenge
I knew that we would get the insulation right. But I had absolutely no idea that we would get the airtightness right. And the airtightness, it’s like a stop go thing. It’s like blowing up a balloon. If there’s a hole in it you will get found out.
The biggest worry would be areas where the airtightness layer gets hidden by the construction.
Interim airtightness tests highlighted areas that needed attention
Guys likens airtightness to ‘compliance’ in the corporate world. He suggests that those in charge of the results should almost be separate from those doing the work.
Pressurising the fabric of the house and using smoke pens to identify leaks was essential to eliminating draughts and improving airtightness.
Airtightness is really about chasing down your problems.
Pausing construction to perfect the airtightness is not realistic
In an ideal world the required airtightness would be achieved before any finishing work was carried out.
With a team of builders on site it becomes increasingly difficult to address small airtightness issues without progressing work elsewhere in the building.
Delays in ordering increased pressure
With supply chain issues the sequencing on this project added another layer of complexity. Lead times could change overnight.
Architects’ contract administration a good call
One of the more valuable things we did was to engage with my architect in an administration contract, which included a fortnightly visit on site, and that kept a level of professional focus on what was needed, what was coming up, where the timing was, what was being realistic, etc.
The Passivhaus standard became a step too far
EnerPHit is the retrofit standard for a reason. It is hard to modernise existing buildings and this is why it’s a slightly less stringent target.
Although Guy held onto the goal of achieving the Passivhaus standard target of 0.6 air changes per hour (@ 50 Pa) until the ‘grim death’ there came a point where he realised it was too much of a stretch.
Work in the basement apartment had been halted to focus on the main house so that Guy and Susan could move back in as soon as possible.
So the first ‘official’ airtightness test of the main house was after they had moved back in (March 2022). At this point it became harder to carry out remedial work.
And an airtightness test for the basement was still needed for an overall result (which came a few weeks later).
The final result for the whole house was 0.95 (ACH @ 50 Pa).
Knowing the ‘Hurculean’ effort that went in Guy is immensely proud.
That’s what the EnerPHit standard is about… recognising the almost exponential effort in getting from 1 ACH to 0.6 ACH (@ 50 Pa) in a property that’s already built.
Comfort tops the benefits
Guy laughs about being able to wear shorts and a t-shirt almost all year round!
He also points out how quiet and still the house is.
With an all electric house the bills are likely to be 1/5 of what they were before, but clearly there has been a massive upfront investment.
Solar PV is the only missing element!
In some respects the people I’m feeling most envious about today are those who have 10 kilowatts of solar PV on their roofs.
With an efficient heat pump providing heating and cooling for the house as well as the hot water, Guy has got nearly everything for the resilience and future-proofing he wanted.
However, there were not many good options for a solar installation. The flat roof at the top of the house was the obvious one but it only had a couple of kilowatts potential.
I didn’t think that that was worth the trouble, to be honest. But given everything else that we were doing, it was just probably the straw that broke the camel’s back.
Good communication and a stable relationship with your builder is vital
Having been through building processes before Guy has been reminded how important it is to have a stable relationship with your builder. The key to this is staying calm and talking through any challenges.
Changing your builder is a vastly complicated process and it’s made even more so when you’re halfway through a Passivhaus. And you wouldn’t find another builder to want to take it on. So having a strong relationship with the builder is super important.
There is an appetite for retrofit in the UK
Guy has already opened the doors of his home to local community groups interested in retrofit.
There is an enormous appetite in Oxford, and I think probably UK wide, for all or some or most or half of the things that we’ve done to our property.
Watch our documentary of the Kinver project in The Hub
Find out more
Check out part 1 – our interview with Guy before construction began
Twice a year Passivhaus dwellers open up their homes for you to have a look around, experience the level of comfort, gain insights into best practice and ask any questions.
Kit Knowles from Ecospheric explains why he is driven to keep pushing further in pursuit of sustainability in building projects.
Kit Knowles (Rick McCullagh)
Interview with Kit Knowles
Despite his university education and early working life being in the field of chemical engineering, Kit quickly realised that this wasn’t for him. So, around 14 years ago, he committed instead to renovating and decarbonising a newly acquired 1909 arts and craft dwelling while he considered the direction in which to move his career forward.
The SuperHomes network and trade shows provided information and inspiration
Kit took an external wall insulation approach to his property and came up with a detail using three layers of Spacetherm with a PIR backing board. This would keep the profile relatively slim and maintain the aesthetic of the facade.
The Thorns (Colin Poole)
In order to fully research his proposed methods, he gathered information from attending trade shows and visiting homeowners of SuperHomes. SuperHomes is run by the National Energy Foundation, and is a charity that permits homeowners to join the network if they are able to reduce their home carbon usage by 60% or more. They are then able to open up their homes to share their methods for other people to reapply the solutions to their own properties. Kit credits SuperHomes with putting him in touch with a network of people where he could find out what others were doing, what they weren’t doing, and how he could push it further.
Getting hands-on in the project working alongside his team of builders meant that Kit had a great insight into specification details and why they were often flawed when it came to installation, thus leading to a performance gap.
The Thorns (Colin Poole)
He started his business off the back of his own renovation project
When Kit opened his own home as part of the SuperHomes network, he realised there were a large number of problems that he had solved, that other people hadn’t. So when he had five or six people asking for his help in explaining how he had done it, he decided to establish his own consultancy, although it did take him another few years to master the dark art of timber and damp!
The Thorns (Colin Poole)
After several years of chasing larger and larger projects, Kit came to two uncomfortable points of realisation:
The full decarbonisation of the planet was never going to be impacted by what he was doing, given the scale on which he was doing it.
That those that were doing the most carbon damage were those that were the biggest consumers.
Clients can dilute the environmental ambitions
Coming in late to a project is problematic because many decisions have already been made and there is little desire to start over. On one particular mansion he was not able to have any impact on the design of the house and his only option was to look to renewables for efficient energy generation.
He had however managed to keep everything on a single-phase power supply rather than a three-phase… until at the last minute the client decided they wanted to heat the stair treads, which could only be done with direct electric, resulting in tipping the whole system over!
Aesthetics matter
From that point, Kit focused on how to develop more meaningful decarbonisation projects, and key to this were his interactions with Kevin Anderson from the Tyndall Centre. His advice was based on the iPhone effect of creating something that people didn’t know they wanted or needed, and then when they had it, couldn’t do without it. The only way to do that was to have full control over these builds and treat them as demonstration projects.
And so the development arm of his business began, kicking off with Zetland Road. It was everything they had learned up to that point, put into a single project to see how far they could go. Despite not chasing Passivhaus certification, they ended up with Passivhaus Plus, together with eight world firsts.
Zetland Road before renovationZetland Road after renovation (Rick McCullagh)
“Here, we were trying to get the combination of the technology with the look and feel. If it’s a bland Germanic box, it wasn’t going to revolutionise anything. It had to be old, it had to feel authentic and original. And it also needed really to be pretty sexy.”
By hitting the largest sectors they could make the biggest carbon impact
With the construction industry being the largest contributer, at 40% of the country’s carbon emissions, Kit wanted to narrow down further into where the biggest carbon reductions could be made. With existing buildings being 80% of that amount, they could keep breaking that down further to select the projects where they could make the most impact. Of particular interest to him were the around half a million or so Grade II listed buildings.
Kit uses a three level approach:
Passive design techniques (ie orientation, glazing ratios etc). Thinking about how to use something differently, and using a quality roadmap to get as much for free as possible, such as free energies, or conservation of energy.
Fabric. The idea that you can improve on airtightness and insulation levels throughout the building.
Efficient or renewable energy. With the priority being numbers 1 and 2, hopefully there is little need for this.
Lymm Hall is giving him the chance to trial new approaches
Kit considers himself an opportunist, so when the chance came to purchase the Grade II listed, moated, 1570 country house of Lymm Hall, he and his family relished the chance to take the project on. It also came with a paddock that had planning permission for five detached new builds.
Lymm Hall (Lymm Photographic Society)
Their initial modelling estimated the energy usage would be around 470 kilowatt hours per square metre to heat to 20C all year round!
It doesn’t cost anything to think how something could be done differently
Trying to reduce that as far as possible has led to some fascinating innovations, such as developing a method where you can co-pressure test just one room (using the Pulse method) which means you don’t have to test the whole building. This means they can tackle different rooms in different ways and compare directly what their performance is like. For example, some floors they’ll be able to use underfloor insulation, whereas others are decorative floors that are protected under the listing so can’t use that approach. This should give them the ability to treat the areas in different ways and have a scientific method of comparison.
“For the first time, we’ll actually have granularity over which components of upgrading a building made the most significant difference, because up until now, as a consultant, I can say, well, if you combine all these things together as a holistic approach, you will go from x to y in terms of performance, but what I can’t say is specifically out of those 10 things we do to your building, which is the first and the second and third most effective. It’s very, very difficult to get that granularity which this will offer.”
Lymm Hall (Lymm Photographic Society)
Achieving Passivhaus Premium on multiple dwellings will be a world first
Alongside the main Lymm Hall project, they are also building their five detached houses in the paddock using modern methods of construction without any petrochemicals or concrete, with the ambition of achieving the Passivhaus Premium standard. There aren’t currently any Passivhaus Premiums in the UK, and to achieve five on the one site would be the first time that has been done anywhere globally.
Another project is a series of barns that they are converting for ecotourism and making completely off-grid for water, electricity and waste.
They are also working on an old sorting office in Levenshulme where they are trying to create the world’s first zero waste, zero energy food hall. It will have multiple kitchens, restaurants, brewery, roastery and zero waste deli.
Kit is very aware that agriculture is also one of the largest contributers of carbon emissions, and is working alongside clients to do a lot of work around food and energy. This is around agroforestry in the main, looking at building products and food production, and also large scale energy production from estate lands.
Andrew Reardon from ProAktive explains the insurance options that are available to anyone carrying out a self build or renovation.
Interview with Andrew Reardon
Andrew Reardon is a Senior Account Handler at ProAktive, a company that specialises in insurance and risk management. He works in the self build department, providing insurance for new builds, renovations and extensions.
Self build insurance has similarities with standard house insurance
It covers many of the same things as traditional house insurance would, such as cover for theft, accidental damage and fire, but also covers you through the construction phase. The biggest difference between the two comes from the types of claims involved. Many of the claims they receive are related to thefts from the construction site, because they don’t have the same level of security that a larger developer would have and therefore tend to be targeted. They also receive many public and employer’s liability claims, where injuries occur to workers on site, or to members of the public who may have wandered onto it.
Employer’s liability and public liability are covered
The employer’s liability provides cover for if you are held negligent for an accident that occurs on site. If you have hired a main contractor or have sub-contractors on site, then they should all have their own public liability insurance, but your self build insurance will be a fallback in case that fails or there are any grey areas. It also covers for claims related to casual labourers, or friends and family that might be helping out on the site who wouldn’t carry their own public liability insurance.
Check your contractor’s insurance cover
Rather than waiting until there’s been an incident on site and asking your contractor for their insurance details, it’s far better to get that information in advance of starting and steer clear if they can’t provide it. Even if you’ve employed a main contractor to run the job, you’re relying on them to make sure they have contract works cover, are keeping up with their payments, and have the right limits to cover the value of your project. If they don’t have the correct levels in place then their insurance won’t be sufficient, which is when your own cover can provide the fallback.
Theft is by far the most common cause for a claim
Andrew says that they don’t have too many claims for accidental or malicious damage, but the most common ones after theft tend to be for damage caused by storms, leaks and frozen pipes.
Theft tends to be of machinery and tools, rather than materials, so quite often a self builder will build the garage or other outbuilding first in order to keep these things more secure.
Other things that can help to reduce the incidence of theft, is to use fencing to keep people off the site, which also helps in terms of public liability, and CCTV if possible. Having a sealed container on site will also help with security, as will keeping deliveries of boilers and kitchen items out of view or away from the site as much as possible until they’re installed.
Keep your invoices and receipts safely together
This will help in the event of needing to make a claim, as you will need to provide evidence of your purchase. Having quick access to these will help speed up any claim too. If you don’t have a traditional receipt for things like eBay or other second-hand purchases, then make sure you keep copies of emails or take photos of things to prove what you have bought and that they have arrived on the site.
Andrew gives the example of one claim which was for the theft of a £20,000 roof which had only been delivered the previous day. In that case, the delivery driver had tipped someone off that it would be there and unsecured. His advice is to be fully aware of everyone who is on site, and even take note of IDs. Most importantly, secure the items whenever possible, ideally by installing them straight away.
One point to note is that you can only insure things like machinery and tools that belong to you or that you hire in your own name. A contractor or other tradesperson on site will be responsible for insuring their own tools and equipment.
Renovation projects might not be covered under your standard household policy
People often assume that their standard house insurance will cover them throughout a renovation project, but often that’s not the case. It may depend on the level of work that is being undertaken at the property, and particularly if the work involved is structural.
Your first step in this situation should be to contact your household insurance provider and advise them of the works to be carried out, to determine what cover they can provide. Your existing standard policy wouldn’t cover for the new elements of the work, such as the fixtures, fittings, and materials once they arrive on site, so a policy should be taken out for this. Your existing insurer also would reject a claim for something like a fire caused by a tradesperson on the property, if they haven’t been notified in advance of the works.
Carefully consider what your renovation policy needs to cover
The main thing to consider when selecting a policy for a renovation project is that it will cover your existing structure, as it will often be unoccupied during the build. Also notify the insurers of any intrusive work that will be carried out, such as deep excavation or piling which have the potential to cause damage to neighbouring structures. Depending on the nature of this work it can also be worth considering an additional non-negligence cover, which is designed to cover you in circumstances where there is damage to neighbouring structures through no fault of you, your contractor, or architect. It can be quite an expensive policy, depending on the proximity and value of those neighbouring buildings, but definitely worth considering if you’re doing intrusive work like retrofitting basements.
The next thing to ensure is that it will cover your fixtures, fittings and materials when they arrive on site.
The employer and public liability elements should have adequate limits, so £10 million is standard for employer’s liability, and £5 million is the minimum for public liability. Councils and utility companies generally won’t attend unless you have at least that minimum, so it would be pointless to have less than that.
It’s worthwhile doing a Schedule of Dilapidation
This is a survey of neighbouring structures which is worth doing if you’re going to be carrying out intrusive works that have the potential to cause them damage. Take photos and keep this schedule to show any existing damage to them before you start, to ensure you have proof if these are claimed for later on down the line.
Even keeping photo and video documents of your own progress can be a good idea for if you need to make a claim at any point, such as for total loss due to fire. The more you are able to evidence the better.
The cost of a policy will depend on 3 key criteria
Primarily this will depend on how long you require the policy for, whether it be 9, 12, 18 months or more.
The second factor is the sum that it is being insured for.
And thirdly, the construction type might influence the premiums. A typical brick and block construction would be fine, but something like ICF or SIPs, which insurers might not deem to be a standard construction type, may incur a higher cost.
There may be some projects which insurers will refuse to cover
These would typically be projects of a non-standard construction, which perhaps have combustible elements to them. Particularly since the Grenfell tragedy they have been nervous around projects with polystyrene and wood cladding, forcing self-builders to change their plans or pull out of projects altogether.
Insurance isn’t a legal requirement
Although it’s not a legal requirement it is something which Andrew wishes people would think about before they even start building. There might be reluctance to take a policy out right at the beginning as people think there won’t be many materials and tools around, so it’s not necessary. But actually, even at that early stage it’s important to have the cover in place for the employer and public liability elements. If left too late into the project, a self builder may find they can’t get cover until it’s been signed off by building regs, because until that point it won’t be considered by a normal household insurer.
Ben Adam-Smith recently featured on the Passive House Accelerator podcast, hosted by Zack Semke and Matthew Cutler-Walsh. You can listen to the episode here.
Guy Hargreaves explains why he wanted to renovate his Victorian terraced house to Passivhaus standard and how this is going to be achieved.
Interview with Guy Hargreaves
Guy Hargreaves is originally from New Zealand, but he met his wife Susan in Australia.
While living in Sydney they bought and renovated a Federation style house in which to bring up the family. When the children were in their early teens, they relocated to Hong Kong with Guy’s work. And after 11 years there, they followed their children to the UK (where they had gone to university and settled).
As Susan was doing a masters in Oxford that became the obvious place to set up home and in October 2019 they bought a Victorian terraced house. Initially they planned to live in the house for a couple of years to get a feel for it, but it quickly became clear that it would need a lot of work to make it liveable. So they started planning a renovation straight away.
The building is set over four floors and includes a self-contained basement flat and converted loft.
A visit to the National Self Build and Renovation Centre was a great starting point
While Guy and Susan were able to lean on the experience of their previous renovation, they were keen to upgrade this property to be a high performance home.
After seeing several Passivhaus homes on Grand Designs over the years they had become interested in the concept, but it was a visit the National Self Build and Renovation Centre (NSBRC) that acted as a catalyst for targeting Passivhaus standard. This is also where they met Alan Budden from Eco Design Consultants, who they would later hire as the project’s architects.
Having studied mechanical engineering at university, Guy felt that discovering the Passivhaus standard was a bit of a homecoming.
“The Passivhaus concept itself really grabbed my imagination, to be honest, and I was hooked.”
Working remotely caused minimal delays
Having gained planning consent (in January 2020) with help from a more ‘traditional’ architect, Guy realised that they needed a specialist for the Passivhaus refurbishment. So they hired Eco Design Consultants to take over the project.
This coincided with the beginning of the global pandemic and consequently the project was progressed during lockdown.
Despite this challenge Guy believes it made little impact on the project’s timeline.
Preserving the ‘period’ feel is important
As part of a three terrace development, Guy was keen to keep the heritage feel of the property at the front.
“We don’t want to replace Victorian sash windows with anything that doesn’t look like the Victorian sash windows that are there now.”
The rear of the building is less important because most houses have been extended over the years and they all look different.
Sketch perspective of the how the rear will look after the refurb
Passion is a driver for targeting the Passivhaus
This renovation will be to Passivhaus standard rather than the slightly less stringent retrofit standard, EnerPHit.
Guy is hoping that it’s not going to be a much heavier lift.
“It’s the passion I have for the Passivhaus certification more than anything. I’m not sure that the internal feel of the property will be much different if it was renovated to EnerPHit certification.”
First floor plan
There are different insulation strategies for different elements of the building
The historic brick facade will remain at the front and back, but it will be insulated internally.
At the back of the house the ground floor will be dug out and a new concrete slab will be set on top of insulation.
In the basement, the top of the floor will be taken off and a Diathonite screed will be laid down.
Interestingly, the party walls will not be insulated at all.
The windows need to be replaced
All windows and doors need to be high performance, so these will be upgraded to triple-glazed products.
The whole building will also be ‘wrapped’ internally for airtightness layer. This layer will come in the form of various materials.
‘Futureproofing’ the building justifies the cost
Guy admits that there are significant costs attached to a renovation of this quality and performance.
However, he bought at a price that reflected that the property needed a full renovation. Also, part of retrofitting this home is to futureproof it against the impact of climate change and rising energy costs.
On top of that, there is no doubt that the comfort levels of the house will be vastly improved and this too, along with Passivhaus certification, may be reflected in what the property will be worth in future.
Their builder was keen to develop skills
Finding a builder with Passivhaus experience was really hard.
So Guy has hired a firm who have considerable renovation experience but also demonstrated a desire to tackle a project of this nature.
PHPP adds another dimension to the project
In addition to balancing cost, quality and speed, Guy says you must always think about performance.
“You’re always trying to balance what you want to do stylistically with what the PHPP model will let you do! So that becomes a fourth dimension. Everything you do has an impact in terms of, will the building perform the way you want it to perform?”
Guy and Susan started their renovation journey at the UK’s only permanent exhibition centre for self-builders and renovators – the National Self Build & Renovation Centre.
Located just outside Swindon it’s a one-stop shop for learning about the build process and sourcing potential suppliers.
They also offer a range of courses and workshops. Find out more by visiting their website.
Author Roger Hunt explains why period properties need treating differently when it comes to achieving successful retrofit projects.
Interview with Roger Hunt
Roger Hunt co-authored Old House Handbook back in 2008, about repairing old buildings, at a time when retrofit was barely on the agenda. Not long after, people started to recognise the importance of retrofit and sustainability which led to their companion book, Old House Eco Handbook. It has since been updated with a second edition, incorporating new thinking on how to make buildings energy efficient, and the surge of new materials available that can make it happen.
Not enough progress is being made
Roger recalls attending a conference not long after Old House Handbook was published where, to meet targets, it was claimed that a city the size of Coventry would need to be retrofit every week.
“We’re nowhere near that. We haven’t scraped the surface. We are so far behind in terms of retrofitting old buildings that there is absolutely no way we’re going to meet the targets we need to meet as far as I can see. And we can’t build new homes to solve the problem because we can’t build them quick enough; there isn’t the land to build them on. And the environmental impact of knocking all the old ones down to build new ones isn’t sustainable either.”
Typical UK housing stock – Copyright Roger HuntCopyright Roger HuntCopyright Roger Hunt
Pre and post-1919 buildings need treating differently
Roger defines old buildings as being anything from medieval through to Victorian and Edwardian terraced houses. They were houses typically made from breathable materials, such as lime mortars, renders and plasters.
Getting the retrofit techniques wrong in a breathable type of construction can store up problems for the future in terms of damp and condensation.
It is important to make the distinction between those breathable buildings, and ones from around 1919 onwards, when construction methods changed to concrete and cement being used with a focus on keeping water out. Those buildings need to be treated differently, as getting the retrofit techniques wrong can store up problems for the future.
Start with a plan for the whole building
It might be that you won’t intend to do a full retrofit straight away, just elements of it to begin with and the rest spread over several years, but it’s important to think of your long term plan of everything that will need doing.
For example, starting by draft-proofing all the windows and floors will cut down air movement within the house and cause a build up of condensation and poor air quality, if controlled ventilation isn’t considered. That might be achieved by controlled opening of windows, or a mechanical ventilation system.
Using controlled ventilation – Copyright Roger HuntOpening windows as a form of controlled ventilation – Copyright Roger Hunt
Roger says that some sort of mechanical ventilation is almost inevitable, particularly for kitchens and bathrooms, but heat recovery systems don’t necessarily work well in old buildings.
Reducing drafts is as important to comfort level as insulation
Drafts actually make you feel colder than the building really is, so introducing secondary glazing or draft proofing around windows can make a big difference to comfort levels.
Other uncontrolled ventilation can come from gaps in floorboards. If they can be plugged and a window opened when required then you can have controlled ventilation.
Copyright Roger Hunt
Buildings must be properly maintained
Roger stresses that maintenance is particularly important for old buildings. Blocked gutters for example can lead to thermally inefficient wet walls, and a slipped roof tile can lead to leaks, rotten timbers and water coming through ceilings. The repair job is going to be costly and a lot less sustainable than just maintaining the building properly.
Copyright Roger Hunt
Reduce energy use within the house
Before even thinking about how to heat or light the home, you should be thinking about a fabric first approach of how to insulate, cut drafts, and increase daylight. From there you could incorporate solar arrays or air and ground source heat pumps. The heat pumps won’t work so well if it is a leaky building, so these all need to be considered as part of the bigger project.
“You have to think of the best solution for heating combined with all the other things you’re doing. So, an air source heat pump is not necessarily going to be the solution until you have tackled some of the other issues with the building.”
Simple things that can be achieved quickly with an instant impact include changing high energy bulbs to LEDs and putting in loft insulation.
Copyright Roger HuntCopyright Thermafleece
EnerPHit projects can be incredibly successful
With fairly disastrous consequences to getting it wrong, one way to have a successful outcome is to work towards the EnerPHit standard. This will probably mean employing an architect or other specialist with experience of what they’re doing. It might not be cheap or easy but will deliver on energy efficiency and comfort.
There is a delicate balance between sustainability and retaining character
A risk of coming in and doing a complete retrofit of an old building is that it can lose some of the character which makes us love them in the first place.
“I’m passionate about trying to make buildings sustainable and cut our carbon but at the same time we’ve got to have places that are accessible, enjoyable and important to people.”
Roger says it’s a complex subject as we have to embrace the value of the building in terms of beauty, aesthetics and our love for them, along with the monetary value.
Take time to understand your building
Roger’s tips for tackling a renovation of an old building are:
Don’t rush in. Live in an old building for a year, through each of the seasons, to really understand the damp and the light. That will also help with your interior decoration.
Don’t try and use modern materials that are incompatible with an old building. Particularly don’t use an insulating material that is going to stop your building from breathing.
Do your research, talk to people, go to events, look at products, don’t trust everything you read on the internet. Cross-reference everything to check that you have the right solution. What might be right for one building isn’t necessarily right for another, even in the same terrace.
