Tag: healthy homes

HPH392: What’s the difference between good and bad retrofit? – with Marion Baeli

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.”

Find out more

Residential Retrofit (second edition)

Retrofit Revisit report

National Retrofit Hub

Passivhaus Trust

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December 1, 2025
HPH378: Accessibility for all – with Guy Harris

Guy Harris from AccessiblePRS explains why accessible housing is important, what the key considerations are and how to deliver it well. He also shares his experience of designing his own house as a wheelchair user.

Interview with Guy Harris

Guy Harris is the Director of AccessiblePRS, which he founded in 2020 to increase the supply of wheelchair accessible rental homes. He became a wheelchair user in 2003 after an accident and now works to promote good accessible design for all buildings.

Accessibility is the ability to move around a home at all stages of life

Quite often the terms accessibility and adaptability are used interchangeably, and people will even have their own understanding of what they mean. So Guy defines accessibility as the flow and space of a home, and the ability to move around it at all stages of life. This can be as parents with young kids, older people, wheelchair users, people who have dementia, and so on. Accessibility is understanding how we relate to our spaces and making them human centred.

Accessible spaces can benefit everyone

Guy believes that making accessibility about the person with a disability is fundamentally flawed, because it means we bring all our negative stereotypes and misconceptions to that approach. Instead of being a burden this can be playful, glorious or liberating for a whole range of people.

“When I tell stories about where accessibility is in place, very often, I tell them about people who have no disability at all, and show them the advantages, so that we can understand that this really is not for some people, this is for all people.”

Wheelchair users face constant frustrations from existing properties

In 2003 Guy made a mistake when crossing the road and was struck by a lorry. From that point he became a wheelchair user.

Like his, most disabilities are acquired and this made him realise that he had been part of the problem before his injury. He worked on property projects, and it was only after the accident that he understood the constant frustrations for wheelchair users around property, which also gave him an insight to the opportunities.

Funnily enough, before his accident, Guy had bought a 1000 square feet shell apartment in London, which he made into an aspirational and indulgent space. It was only afterwards that he realised he’d actually designed a wheelchair accessible space. However, he admits he wasn’t in the wheelchair accessible mindset at the time. The Disability Discrimination Act had just come in, which meant that sockets and switches had to be at a specific height. He remembers clearly saying, “I don’t have a disability, I don’t want them at this height, I’m not doing it.” He sees a nice juxtaposition there, both wilfully not wanting to do anything around disability, whilst on the other hand designing the perfect space for it.

Building for accessibility requires a mindset shift

While we have made significant advances in gender equality, eliminating racial discrimination, and LGBTQ+ rights, Guys says that disability feels like the poor cousin.

Until we get over our subconscious fear around what it means, what it looks like, and not wanting to believe that it can ever happen to us, we’re always going to have an issue with the idea of building accessibly.

Guy feels we either need to change our relationship with disability, or perhaps with the language around accessibility. Accessibility is simply good design.

No one will come into this home and go, “Wow look at that accessibility.” It really features disability in a wonderful way. You come in and you go, “Hey, wow, look at this home.”

Key requirements for wheelchair users are more space, a level home, step-free access and a purpose designed bathroom

As a wheelchair user Guy needs things to be designed in a certain way to be able to live autonomously and independently. He needs a bit of space, wider doors and consideration of how they’re positioned relative to things that come next to them, whether it’s cupboards or walls. Step-free access is also important, which might include lifts or ramps. Bathrooms are a critical room, often a wet room, and a hoist may be needed.

By designing for a wheelchair user, you design for any eventuality in life.

You don’t need a specialist architect for a house build

Guy’s architect wasn’t a specialist in disability or accessibility but was amazing. He drew the brief out of them carefully, in the same way that he would for any other client, considering how they lived and wanted to live.

One aspect that really helped Guy was a study trip, visiting existing properties and trying to absorb useful information.

“People make decisions without actually seeing what they’re making decisions on, which is nuts, frankly. And so the more we got to see different things and understand the implications and the benefits and the costs, the more we naturally arrived at the decisions we made.”

There will be opportunities in the design process

The design process didn’t revolve around the wheelchair, but as they went along, they realised that there were opportunities coming from their discussions. For example, the spine wall down the middle of the property, has quite a few structural posts. These created alcoves and space to put furniture, but also were the perfect place for handholds.

The house evolved into an ecological build through the design process

Guy explains that they were starting with a blank sheet and ecological architecture or doing something green, was an obvious question to ask, although at that point he really didn’t know what it meant. He did some investigating but wasn’t getting anywhere until he heard a sustainability consultant talk at a show and he’d never heard anyone speak so much common sense about how to build. She then recommended the architect, who he eventually hired.

“We arrived at straw, having said the only thing I know I don’t want is straw!”

After two separate non tangible experiences they decided to build with straw. The first happened in Scotland when they visited a straw bale building. It was blowing a hoolie outside and because Guy is paralysed, he doesn’t feel his legs, but his legs started to tingle in a warm, cosy, enjoyable way. They then went to the property next door, which was a different build and a nice layout, but it just felt cold, without the same richness.

This prompted them to visit another straw build, Haringey Community Centre in London. At the time Guy’s wife was pregnant and wasn’t really enjoying the pregnancy, nausea, low blood pressure, always moving from side to side. But inside the centre he noticed she was standing still and looked comfortable. As soon as they went back outside the nausea started again, but when they came back inside it stopped. There was no way of understanding what it was, but on two separate occasions they had both experienced this magical feeling, and so it became a no-brainer to build with straw.

Accessible homes don’t have to be ‘Grand Designs’ projects

Guy is aware that his bespoke home might be considered a grand design style building, but accessibility can be achieved at most scales.

Aspects Guy particularly enjoys is the volume of the internal space and how light is brought into the property from all directions. There’s a strong connection to the wooded area outside.

Their choice bio-based materials has delivered on many levels

Guy’s home is a load-bearing straw bale house, with bales almost being used like bricks. On the inside natural clay plaster is applied directly to the straw, whilst the outside is lime render.

The house has an organic, natural feel whilst still being mainly straight lines with a few nice curves and subtle colours. For Guy the house feels grounded and is peaceful and calm inside. The design is largely open plan, which allows them to be doing things together in the same space, but also when doing things separately they somehow still feel connected.

“I think one of the subtle things about the house is how when you’re in it, everything feels right.“

Look at the value of what you build rather than the cost

Guy wishes there was more consideration around value rather than looking purely at cost. Building the cheapest possible home is unlikely to deliver a good outcome. As someone who works in property, Guy understands that the budget could be spent in a million different ways. For example, they could have had more space for the money or built more quickly, or spent less, but that was not the priority.

The materials they were using and how they were building was important, and he was taking a long-term view. Guy intends to stay in this house for the rest of his life, so the initial cost will balance out over that time. This is a quality-of-life investment.

An accessible entrance

Make sure you get good advice when building for accessibility

Building and designing homes is an expensive business and it’s easy to make mistakes around accessibility, so Guy suggests getting external input when required.

“If you want to design for more possibilities, take advice. If you want to, I don’t know, have specific sound or acoustic attributes or engineering attributes, you pay for advice.”

He shares a couple of examples of how planning upfront can help you avoid problems further down the line.

He stresses that it is important to consider how the walls, doors and windows relate to each other. How you create the ratios and the space, your floor surfaces and the furniture that you need. Bathrooms are an expensive room that need designing properly, because retrofitting a standard bathroom to accommodate grab rails or a ceiling track hoist, could mean starting again from scratch.

Another scenario is with sliding patio doors, which may not open all the way, meaning the opening is then less than a wheelchair width. Or you put a ramp in but have forgotten that you need a level platform on both sides. These are simple things, but they matter and so paying for advice could help prevent costly mistakes.

“In every design meeting, just ask the questions, what can I do? What if? What does it look like? What does that mean? Have we thought about? Do you know about? And take it from there, because even the simplest of questions will inform the design and make people think.”

The regulations are helpful but provide minimum standards

Guy says that, for the most part, the regulations are extremely helpful. However they are open to interpretation and deal with minimum standards. If you have a designer who doesn’t understand the intention behind the regulations, they can interpret them, sometimes in bizarre ways which mean the regulations have been met but are meaningless. And for Guy when we aim for minimum standards, we nearly always fail. Good design is about understanding what is actually needed and designing for that. If you go for best practice, then the regulations are almost guidelines. Experience and advice will steer you much further.

There is a National Register of Accessibility Consultants, NRAC, and those are people who have experience of designing for accessibility. A consultant can come in at the beginning, at the design phase, be part of those conversations and reviews, and support your architect in optimising the design.

We should be designing for an ageing population

By 2040 there’ll be more people in the UK aged 65 or over than there will be of working age, which for Guy, begs two questions. One, where are they going to live? And two, who’s going to look after them? The only feasible answer at the moment is an end-of-life residential care setting, which he thinks is going to be quite grisly for a lot of people.

It’s already common to find that newly injured people with disabilities get stuck in hospital, because there’s no accessible accommodation available.

So if you have the opportunity to create your own home, it’s a good idea to consider future needs. Otherwise you may face a situation, an illness or a disability, and you won’t be able to cope and you’ll be forced to move out.

Communities should be able to house us all

Guy feels that in the UK we put accessibility in a silo like all the other housing issues, such as affordable homes and green homes, whereas accessibility could cut across all the silos. He suggests every design meeting should ask questions around accessibility to inform the design and make people think.

He gives an example where his architect was working on a community project in Scotland, designing holiday lets in a woodland setting. Initially they were not thinking about accessibility, but when they embraced it several things happened.

The first thing they realised was that by designing the bathroom for accessibility it helped with the modular design and made things flow. The second thing was by making the route from the car park to the homes suitable for wheelchairs they could get a small telehandler to the construction area. This saved time and money when moving materials and the process went more smoothly. The third thing was the community realised that if any of them had an accident or got injured and needed accessible accommodation they would now be able to stay in the community rather than having to move out.

For Guy this is an important point to highlight. Traditionally we’ve always included everyone in a community. We really need to get back to that understanding of what community means.

“One of the things I love to do is show beautiful, accessible design, because I think that’s where people suddenly start to get it and realise that it’s not clinical, institutional, ugly, it’s actually something that nourishes and enhances our lives.”

Find out more

AccessiblePRS

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May 21, 2025
HPH363: Is it worth getting an asbestos survey for an existing home?

Greg Byrne from RB Asbestos Consultants explains what asbestos is, why it was used so widely in construction, its potential impact on health, and how you go about identifying and removing asbestos products.

Interview with Greg Byrne

Greg Byrne is the Managing Director of RB Asbestos Consultants, a company that provides specialist services relating to asbestos including surveys, testing and training.

In this interview Greg gives us a potted history of asbestos, explaining how it became so widely used in the construction industry and what led to it being banned in the UK in 1999. He also stresses the importance of getting an asbestos survey when buying or planning to retrofit a house that was built between the 1960s and 1990s.

One asbestos fibre under a microscope showing it’s actually a bundle of hundreds of thousands of smaller fibres each around a micron in width

Asbestos is a naturally occurring mineral

Asbestos is a natural mineral that occurs as veins in rock and is mined just like other minerals. Whereas minerals such as quartz have small angular crystals, asbestos is composed of long fibres, which when broken down become tiny fibres, invisible to the naked eye and easy to inhale.

After mining, asbestos is broken down into its fibrous state and added to other products, called Asbestos Containing Materials (ACMs).

“We think around 4000 different materials have asbestos in them.

Asbestos has been used for thousands of years

There’s evidence that asbestos was used thousands of years ago to strengthen pots and that the Greeks knew how to spin and weave with it to make mats and other products. It wasn’t until the mid-1800s that western chemists started to recognise its properties, with America then including asbestos in a range of products. For example, some Bakelite contains it. The American company Turners then came to the UK and set up a base in Manchester, so it could expand and supply products worldwide. The early 1900s saw the first use of asbestos in the construction industry, but this was interrupted by World War I and World War II. It wasn’t until the 1950s when rebuilding Britain that the use of asbestos took off in a big way. By the 1960s through to the mid 1980s asbestos was commonplace in new buildings. However, from this point its use started to decline and it was finally banned in 1999.

“There’s almost no part of a building [from that time] that’s not been touched by asbestos, right from the floor to the top of the house.”

Asbestos fibres on a human hair

Asbestos is the biggest killer in construction today

In the UK, the first recorded case of somebody dying due to asbestos exposure was in the early 1900s. It wasn’t until after World War II, with production in full swing, that the evidence starts to build as a number of people die from asbestos exposure in factories. Greg explains that even though a ‘Factories Act’ was introduced and ventilation of factories was brought in, it was not enough to turn things around.

Asbestos doesn’t impact health immediately

Breathing asbestos fibres won’t necessarily affect you straightaway, and some people may not be affected at all, while others will get ill 20-60 years later. One type of asbestos related illness, mesothelioma cancer has the lowest survival rate of any type of cancer. Even though asbestos was banned at the turn of the millennium this is not a problem that has gone away, with 5200 reported deaths from asbestos last year (the next biggest killer is falling from height, which is in the order of 20 deaths per year).

Document exposure to asbestos

Although there’s not much you can do if you’ve been exposed to asbestos, make a record of the incident. This might be useful at a later date if there is any legal action, etc.

AIB asbestos lining to an internal garage ceiling (high risk)

AIB asbestos lining to an internal garage ceiling

AIB asbestos soffits (high risk)

Before buying a property built between 1960 and 2000, get an asbestos survey

Greg explains that RB Asbestos Consultants don’t generally survey buildings for asbestos if built before 1960 or after 2000 as asbestos is less likely to be an issue.

An asbestos survey is similar to a standard building survey, but the surveyor will have been trained to look for signs of asbestos. They’ll go round the building, room by room, taking photos and describing the various construction materials they find. If there is anything they think could contain asbestos, they’ll take a sample and send it to a lab for testing. Your survey report will detail any asbestos found and advise you what kind of contractor you need to do any remedial or removal work. This type of report can then inform your decision on buying the property.

Corrugated asbestos roof

Artex textured coating

Floor tiles and bitumen adhesive are both asbestos

Get an asbestos management survey before refurbishment or demolition work

There are two different types of basic management surveys, one for refurbishment and one for demolition. In both cases you would supply the surveyor with your plans for the work to be carried out and they would target those areas of the building where invasive work is going to take place. In a renovation you might be making holes in walls, lifting floorboards and taking down ceilings. The surveyor will know where to look and be aware of asbestos that might be hidden. For example asbestos packers may have been used around window or door frames.

If you get a chance, remove the asbestos

Asbestos is actually safe when it’s not disturbed and has a reasonably well sealed or bonded surface. It’s only when we actively damage the asbestos, through sanding or drilling or through physical destruction that it becomes dangerous. Leaving it in situ may just store up problems for the future, so Greg recommends removing it when you have an opportunity.

Asbestos surveyor kitted up

When dealing with high-risk materials there is a need to work within an enclosure which is airtight with specialist air movement equipment and high efficiency filters. With lower risk materials there still is a need to deal with the materials carefully with appropriate PPE masks and suits. All the waste is double bagged, sealed and taken to a specialist waste site where it is placed in a clay lined cell. The EU are looking at stopping this method of disposal as they’ve seen evidence of water leaching the asbestos elements out of the landfill back into the wider environment. This may mean super heating the asbestos to over 1200 degrees to turn it into a non-fibrous substance. Greg knows of only one place in the UK that currently treats asbestos this way.

There needs to be better awareness around the dangers of asbestos

Asbestos regulations 2012 are the most up to date set of regulations, which led to approved codes of practice (ACOPS) and appropriate licences to work with asbestos. Greg outlines that at the lower risk end, a one-day training course will give someone the appropriate licence, but also stresses that there is much more awareness raising needed within the construction industry. The regulations allow for a tight control of the process, but Greg points out that enforcement is under resourced.

Greg predicts that his work will get busier with the push towards becoming carbon neutral by 2050. This will lead to more retrofit work on buildings and by default more asbestos surveys and so more asbestos will be found. And because it’s in so many different types of products, a lot of them low risk, it will keep turning up for the next 30-50 years.

Asbestos may not be the only problem material, so wear suitable PPE

Reseachers are already looking more closely at products like fibreglass, ceramic fibres and nano fibres. The HSE are also taking a wider approach and looking at protection from inhaling silica dusts, so it is not just asbestos, we should be protecting ourselves from all types of dust. Greg always advises wearing a mask when working in small spaces that may be old and dusty and you need to get a filter rating FFP 3 for it to offer any protection from asbestos.

Fireplace panel – ribbed pattern at rear

Old vinyl flooring with asbestos coating underneath

An asbestos survey is money well spent

Greg’s main advice is to get your building checked before you buy or sell and even more importantly, before you carry out any major work. A few hundred pounds spent on a survey could save you a lot of money and problems in the long run. And do your own research as you can’t necessarily rely on your builder to do that for you.

Find out more

Visit the website of RB Asbestos Consultants

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October 23, 2024
HPH322 : An EnerPHit standard retrofit of a Victorian mid terrace home – with Guy Hargreaves

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.

Guy stepped in as quality control

Much like Mike Coe’s experience in Portree, Guy decided to monitor quality.

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

Visit the website of Eco Design Consultants

Transcript

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November 2, 2022