Ben Adam-Smith explains why he plans to take on a new mission, and why that’ll mean a slight change of direction and more collaboration.
Ben and his family on their building plot in 2017
A new chapter begins
After 14 years and 400 episodes exploring what we should be building in the 21st Century, Ben Adam-Smith arrives at a natural turning point. The original question — what houses should we be building? — has, in his view, been answered. We know the ingredients: high-performance envelopes (Passivhaus standard), healthy materials, simplicity of form, walkable and biodiverse communities, and genuine involvement of occupants in the process. Rather than continue to revisit territory that has been thoroughly covered, Ben feels a niggling urge to do more with the knowledge, contacts, and credibility he has accumulated. The podcast has been his apprenticeship; now he wants to put that learning to work in actually delivering housing.
Ben’s home and wildflower meadow!
Why the shift, and why now
Tackling another self-build seems unlikely when Ben and his family still love their home and are quite settled. And continuing to make content for self-builders and those planning to retrofit after having closed The Hub membership could only be as a hobby. Therefore, with a new goal, it seems the right time to shift away from bespoke housing. More importantly, Ben has had this impulse to tackle a development before — he tried to pivot towards building just as the pandemic arrived, with a young family and not enough bandwidth to make it stick. The biggest lesson from that earlier attempt was that he cannot do it alone, nor would he want to. Collaboration, he says, is going to be central to whatever comes next.
Sally working on her own project
Introducing Sally Godber and Mike Roe
At the Futurebuild exhibition, Ben bumped into Sally Godber, a director at WARM, the well-known low-energy building consultancy, and a driving force behind the Coaction training initiative. What began as a casual catch-up quickly revealed a shared restlessness. Both felt they wanted to leverage their skills in a bigger, more hands-on way. Ben’s question — “Sally, do you want to build something?” — was met with an immediate and telling response: “I think I might.” That speed of reaction told Ben everything he needed to know about the potential. Mike Roe, also a director at WARM, joined the conversation, bringing deep technical expertise and a grounding in both retrofit and new build.
What the collaboration might look like
The three share common values, a passion for healthy high-performance homes, and a belief that technical know-how is not a barrier. They are open about not yet knowing the precise shape of the venture — whether it will be a single development or an entity that could deliver ongoing value. Early conversations have touched on low-rise timber housing, where margins are tight but the technical scope suits their skill set, and on the possibility of starting small to test the idea before scaling up. Funding options, planning constraints, availability of affordable land and the need for a core team member close to any future site have already been flagged up as potential challenges.
What changes for the podcast
Going forward, the podcast will shift its emphasis from individual self-build and retrofit projects to the nuts and bolts of getting bigger housing projects off the ground — exploring where the opportunities are, what the barriers look like, and how they might be addressed. Sally and Mike may drop in on future interviews or feed in questions behind the scenes. The commitment to high-performance, healthy, low-carbon homes remains the beating heart of everything, but the lens has widened from showcasing finished projects to actively trying to build them.
Bill Butcher and Chris Herring, founders of 21 Degrees, share details of their own group build, a small terrace of three homes in Marsden, West Yorkshire, designed and built to Passivhaus Plus standard.
Bill and Chris on site
Interview with Bill Butcher and Chris Herring
Bill Butcher and Chris Herring, founders of 21 Degrees, have been proponents of the Passivhaus standard since delivering the Denby Dale masonry cavity wall project in 2010. Always open to another challenge to keep them young, Chris has his eyes on being inside his own Passivhaus home before he turns 75 next year. There’s also a community aspect to this because it involves three couples, three homes, one terrace and navigating it all collectively. This is a story about making something happen: pulling on decades of expertise, finding the right people, keeping costs down, and proving that modest, high-performance homes can be built affordably when a skilled group commits to working together.
Existing stable block on the site
Taking calculated risks on land can unlock development opportunities
Chris and Jan purchased a piece of land on the edge of Marsden for a community project, but they also knew there might be development potential for an old stable block on the site. By accepting the risk, they positioned themselves to propose a solution that served both housing and community needs. And even if they didn’t get permission they had a use for the site. In other words they were managing the risk.
Shared values give strength to the group build
The Mount Pleasant Self-Build group formed around a common belief in modest, sustainable living. As Chris explains, he and Jan did not want to live in ‘splendid isolation’, seeking instead a community connection. Having worked with Bill for years, he and his wife Jean became obvious potential neighbours.
“Chris and I have been metaphorically married for the last 35 years!” comments Bill.
Both Jean and Jan were keen that their partners realise the dream of living in Passivhaus homes after spending so much of their careers trying to drive up standards in construction.
Jan had also worked with Veronika a lot, knew that she had been looking into eco housing, and so again bringing in Veronika and Ondrej just seemed to be the perfect fit. Another key aspect of this group was their trust for each other and knowing that at certain stages of the project it made sense for certain individuals to lead.
Emotional resilience is as vital as technical skill in group builds
Jan noted that when one person feels overwhelmed, there’ll be another positive voice in the group. That way the speed of progress or challenges they face don’t feel so bad.
Trust in making decisions collectively
Chris described the Quaker concept of discernment where decisions are reached collectively. You do not always have to decide individually but can listen to others. This collective trust allows for difficult decisions to be made without fracturing the team. Without this support, Jan admitted that she and Chris might not have been so keen to tackle this.
The planning application was a ‘best guess’ at what would be approved
The group chose to stay within the existing footprint of the stable block to minimise visual impact. They also nestled the building into the hillside to keep the ridge height down, dropping the floor level by 1.8 metres. The new building would be clad in timber which is the same material that was used for the stable block. This low visual impact was referenced favourably in the planning decision, although it wasn’t the only consideration. Being sensitive to the context may have helped in this scenario.
Digging into the ground and fitting their designs into an existing form does have an attached cost, but with this consent as a fallback position, there was the option to return to the Local Authority with revised designs closer to what they want. However, the downside is all the extra time it would take, possibly another year, and already two years in they were just keen to move on.
The site occupies semi-degraded land at the edge of the village within the Green Belt. However, it’s defined as a subset called ‘grey land’ which is a relatively new planning policy update. A local landscape architect supported the application on the basis that such land lacks potential. Building housing here protects the edge of the village while meeting housing delivery requirements. It highlights that not all green belt land is equal in terms of planning policy. So understanding the specific definition of ‘grey belt land’ might provide opportunities for development.
Fabric efficiency + renewables makes sense
Most of Bill and Chris’ experience with Passivhaus relates to fabric performance, Passivhaus Classic in other words, but they have come around to the Passivhaus Plus category over time. This delivers everything that we’d expect from Passivhaus Classic, drastically reducing energy use, but also incorporates renewables, so that the building meets all its energy needs over the course of the year.
Chris says decarbonising the grid alone is not enough. The focus remains on reducing energy demand for the lifetime of the building. Renewables act as a complementary layer on top of these efficiency measures.
What may look like waste can often be reused
Although the existing timber stable block could not be retrofitted into a new building it had a much brighter outlook than being thrown on a bonfire. Jean listed it on Facebook Marketplace which resulted in immediate interest from a farmer, who came to dismantle, transport and re-erect it elsewhere. The concrete base was also going to be crushed and reused as hardcore for the new parking area. This approach saved disposal costs and reduced the embodied carbon of the project. It serves as a reminder that a little time and curiosity can find value in waste. Demolition should be viewed as a resource recovery phase rather than just removal.
Site access constraints can sometimes impact how you build
Chris initially favoured off-site timber frame for speed and risk reduction. However, the roads to the plot are often narrow, with twists and turns, and so bringing articulated lorries through these villages was bordering on the impossible. After going through various options Bill got chatting to Mike Whitfield on a motor-biking holiday in Wales and was persuaded that using their stick-build approach with Masonite I-joists would be perfect here.
Early value engineering simplifies design and controls costs
Nick Grant is the Passivhaus Consultant on this project and throughout his career he’s tried to highlight what early value engineering can bring to a project. With this reputation it made absolute sense for Bill and Chris to lean in. They wanted to make their scheme as affordable as possible and part of that was avoiding complexity. In some ways Bill and Chris even saw this as a learning opportunity because Nick Grant, builder Mike Whitfield, services engineer Alan Clarke and structural engineer Andrew Collinson are the dream team! They have been able to pare things down over the years because they work together often, trust one another and can speak openly if they can see opportunity for improvement.
Collaborative humility between designers and specialists improves outcomes
A local architecture firm was engaged on this project. Their skills with space and design would still be required but they were open that they had no Passivhaus experience. Chris saw this as an opportunity for them to learn and develop skills. The key was humility and recognising what the team did not know. Where architects understand Passivhaus, designs are less costly to deliver. However, with so much Passivhaus experience on the rest of the team, in this scenario it was a great move.
One benefit of a group build is to take advantage of individual skills
If you’re tackling a build collectively then there’s a good chance you’ve got some useful skills up your sleeve. For example, Jan is a conveyancing lawyer and so in the early stages she was able to drive through the land acquisition, divide up the plots, and negotiate with neighbouring landowners to tidy up boundaries. With the technical design Bill worked on the junction details to minimise heat loss. He’s also well versed with the construction phase and quite at home with co-ordinating the project. The rest of the group understand this skillset and just let them get on with it!
Bill and Chris as foundation work gets underway
Leveraging long term relationships reduces overheads and manages risk
The project pulls on every favour and relationship built over thirty-five years. The Green Building Company team will handle on-site construction with Bill and Chris project leading. Self-managing the build is an obvious choice here. Drawing on in-house expertise for MVHR and triple-glazed windows contributes to cost control. Bill notes that if they cannot do it for a reasonable price, few others can. Currently they are hoping to deliver the project for under £3,000 per square metre. Bill says that from general chat at last year’s AECB Conference a typical figure for a one-off Passivhaus might be more like £3,500 per square metre.
In terms of finance the plan involves mortgaging their existing homes rather than selling up. Chris comments that the cash flow will be tight at certain moments but they know what they have to do. Navigating finance before knowing the full cost is a familiar tension. Timing is everything when staging the drawdown of funds. This approach requires discipline to ensure the project does not stall. It is a reminder that financial planning is as critical as architectural design.
This is an opportunity for a younger generation to get on the housing ladder
Bill highlighted that Veronika and Ondrej are getting their first home through this scheme. With massive challenges for first-time buyers this illustrates another way of thinking, that an older generation can bring younger people into these projects. The conventional housing market offers working people almost no realistic path. Demonstrating that Passivhaus Plus is achievable at the upper £2,000s sends a vital message. Modest houses built well at a price that doesn’t require a fortune are possible. This intergenerational transfer of opportunity is key to housing sustainability and sets a precedent for future collaborative developments.
Find out more
21 Degrees — Supplier of all key elements for Passivhaus Plus and low energy buildings: MVHR, windows, airtightness products, specialist insulation, air source heat pumps and photovoltaics.
Green Building Company — The independent construction team carrying forward the building expertise developed over nearly two decades within Green Building Store (now 21 degrees)
Mike Whitfield Construction — Specialists in stick-build Passivhaus housing who are assisting with the methodology and frame installation for this project
Hawdon Russell Architects — the architecture lead on this project who are also upskilling in Passivhaus
Jon Broome and Nick Grant explain why they have written The Good Building Book, what’s in it, who it will help and how best to put it all into practice.
Interview with Nick Grant and Jon Broome
Architect Jon Broome and engineer Nick Grant have years of design and construction experience between them, and have set out to share their knowledge of creating how to make buildings that work. Their book, The Good Building Book, is an attempt to cut through the greenwash and distil practical, hard-won lessons from decades of hands-on experience. Rather than producing an encyclopaedia of building, they chose to write from what they actually know — self-build, community projects, Passivhaus consultancy — and then explore how those insights ripple outward to anyone procuring or inhabiting buildings. The result is a book that asks uncomfortable questions about celebrated projects and invites readers to do the same.
“It was an idea of trying to distil the sense out of ‘greenery’ and come up with something practical and useful in how people design and build.” — Jon Broome
Finding examples of ‘great’ buildings is not as easy as you might think
The title The Good Building Book is deliberately modest. Jon and Nick suggest that it’s easy to improve buildings but difficult to create ‘great’ buildings that are universally loved. You can however deliver buildings that perform well, are cost effective and look beautiful. Sadly a lot of prize-winning architecture fails the people who have to live and work inside it. All too often buildings are treated like sculptures, which quickly eats into the budget.
Users deserve a seat at the table
One of the book’s recurring themes is that the people who will actually use a building are routinely excluded from the design process. Jon traces this to a cultural problem in the UK around trust — a reluctance to believe that ordinary people can make sensible decisions about the spaces they inhabit. On the continent, collaboration between professionals and building users is far more common. The book argues that involving users isn’t just democratic; it produces better outcomes, because residents understand their own needs in ways that no brief can fully capture.
“We must make sure that the users of buildings, the residents and so on, are respected and understood and that they have a role to play in the design and construction and management of buildings.” — Jon Broome
End users should upskill too
Nick is particularly keen that the book reaches not just architects and students but the people commissioning buildings. If end users understand a bit more about design process, and what commonly goes wrong, they are in a far stronger position to challenge what they’re being told or sold. The book aims to give people the tools and confidence to question their designers, select the right team, and push back against decisions that don’t serve them. For Nick, this is perhaps the most radical thing the book can do.
‘Best practice’ evolves over time
Both Jon and Nick have built their own homes, and neither pretends they got everything right. Jon’s house, built thirty years ago using massive timber construction, is relatively modestly insulated and very leaky by modern standards — he wishes he’d met Nick sooner to get a better handle on performance. Nick’s straw bale house was inspired by the Segal method, and Pat Borer and Cindy Harris’ book Out of the Woods, but over time he came to see that the material itself is only part of the overall picture and matters less than how you build. Both Nick and Jon are always learning and pour a lot of their first-hand experience into this book.
Nick’s self build home
Materials matter less than how you build
While Jon and Nick have a fondness for timber and bio-based materials, they say that material choice is only one part of it. What matters more is the process — how the building is designed, how it performs, whether it’s affordable and repeatable. Nick points out that a huge building full of bio-based materials that costs a fortune is not inherently sustainable. The book also encourages doing your own thinking and debunking. For example, building a house out of a really sustainable material like cork might seem like a good idea, but there’s actually a limited supply in the world and it would be extremely expensive.
A good building addresses function, economy and aesthetics
A central tool in the book is a Venn diagram drawn from the Vitruvian principles of firmitas, utilitas, venustas — but with economy added as an explicit third circle alongside function and aesthetics. Nick explains that too many award-winning buildings hit only the aesthetics circle: they look striking but don’t work well and are wildly expensive. The diagram isn’t prescriptive about what beauty looks like, since that’s subjective, but it insists that all three domains can be addressed.
Start with function, not form
One of the book’s strongest arguments is about where you begin the design process. If you start with a fixed idea of what a building should look like — a dramatic cantilever, a disappearing wall — then performance, cost, and buildability become problems you have to solve backwards. If instead you start with the functional layout, the budget, and the constraints, a form emerges that works. You can always add aesthetic flourish at the end, but it’s far harder to retrofit performance into a shape chosen for its visual impact alone. Vernacular architecture is a result of the process rather than a style — and that process starts with what the building needs to do.
Old Holloway, Juraj Mikurcik’s straw panel Passivhaus
Sufficiency trumps efficiency
When asked whether sufficiency matters more than efficiency Nick is clear: you can never do enough efficiency to compensate for simply having more and more of everything. He contrasts a vast Passivhaus mansion covered in solar panels with a modest, small building like Juraj Mikurcik’s self build home. The larger building may be highly efficient per square metre, but in absolute terms its environmental impact is far greater. Claiming that a huge, efficient building is environmentally friendly is, in Nick’s view, a problem. Sufficiency — building only what you need — is the foundation that efficiency builds on.
Slate House is an affordable Passivhaus
Genuine value engineering delivers better buildings
Nick draws a sharp distinction between real value engineering and what usually passes for it. True value engineering happens when a collaborative team — architect, structural engineer, fire engineer, quantity surveyor, M&E consultant — sits down together and solves problems creatively, often knocking significant cost off a building while improving its performance and buildability. Cost cutting, by contrast, is what happens when a project runs over budget and the nice stuff gets stripped out: wooden windows replaced with plastic, natural flooring swapped for PVC. The first approach bakes good decisions in from the start; the second is a desperate salvage job at the end.
Passivhaus is a tool that can deliver desirable outcomes
The book discusses Passivhaus openly, acknowledging that simply mentioning the word can alienate half an architecture audience. But Jon and Nick treat it as a practical tool to deliver outcomes we want. For detached new-build homes, they see it as close to a no-brainer — you get comfort, low energy bills, and a building that’s easy to live in. For small bungalows, the heating target can be a stretch, requiring very thick walls, and they suggest a slight relaxation of the target might make scaling up easier without meaningful penalty. For flats, the challenges shift to ventilation and hot water distribution rather than heat loss. The key point is that Passivhaus gives you tools for certain problems; for example it doesn’t tell you how to lay out a house or choose materials.
Beware innovation for innovation’s sake
Jon and Nick warn against the word “innovation” appearing in a brief. Genuine innovation emerges organically when you’re solving problems — and that’s welcome. But when innovation becomes a requirement, whether driven by planning policy or a BREEAM credit, it can disrupt the whole process. Walter Segal, Jon notes, believed that designers have a duty not to use their clients’ money for their own satisfaction and ego. The book encourages readers to focus on principles — comfort, affordability, low impact — rather than chasing the latest certification or buzzword.
RUSS is a members-led Community Land Trust
A Community Land Trust is a way to keep housing affordable in perpetuity
Jon’s involvement with the RUSS community build in Lewisham illustrates what becomes possible when people are trusted to organise themselves. The project began with workshops to establish shared principles, then evolved through a two-weekly cycle of group design discussions involving around fifty people selected by ballot. Some residents, such as Kareem Dayes, took on shell units and fitted them out themselves.
What’s special about a Community Land Trust is that it takes land out of the open market, so that it remains affordability going forwards. Jon sees ‘diversity of offer’ as essential to any comprehensive housing policy, because the market simply doesn’t supply what a lot of people want or need.
The space between buildings has an important role to play
One aspect that Jon mentions a couple of times is how we mustn’t overlook the space between buildings: it’s how we understand places, and it’s where community life happens. Too much focus on buildings as objects, rather than as part of an active process involving the people who use them, leads to places that may look good in photographs but don’t work as neighbourhoods.
Janna and Seb Laan Lomas explain the ethos behind their self build which blends low energy design and natural building while reducing plastics in the construction and also minimising waste. The level of detail, the decisions made and the careful use of the budget have been instrumental in delivering this fantastic project, which makes a great home for them as well as a site that encourages wildlife.
Interview with Janna and Seb Laan Lomas
This episode explores pushing the boundaries when it comes to sustainable design. Some projects might embrace the use of natural materials but not excel with performance; others will have an excellent performance but have relied heavily on concrete or synthetic plastics insulation. In fact every step of the way there are opportunities to build more ecologically, promote biodiversity, and create a better neighbourhood. You just need to test assumptions, do your own thinking and allocate your budget wisely. Janna and Seb both work within sustainable architecture – Janna is the Founding Director of Grain Architecture and Seb is an Associate at Architype – and this gives them a massive head-start. However, this project does not need to be a one-off.
“In my view, this is entirely replicable.” — Seb Laan Lomas
A dream and a burning desire will normally lead to action
Janna began conceptualising this specific house design when she was only six years old. This long-held dream evolved over thirty years before finally becoming a physical reality. Janna always wanted something traditional looking, and drew inspiration from English and French country houses. She explains how her design also responds to her lifestyle and preferences. She prioritised how light would hit specific spaces and the flow between rooms. There are good sight lines to the outside from specific rooms. The use of natural materials was also really important and she was looking for a ‘perfectly imperfect’ finish internally rather than something minimalist and white!
Seb describes himself as the silent client in this, although he really wanted the project to be a certified Passivhaus.
The site selection considered orientation and community fit
Having a design in mind before you find a site is slightly unusual. It’s normally the other way around. You find the site and then your designs are a response to that site. So there were plot requirements, although the form of the house is fairly simple which made the task easier. One of the main considerations was sunlight so a south-facing site was top of the requirements, both for the house (solar gains and daylighting) and the various garden projects. Access from the north side was also essential to manage the entrance flow effectively. The rural setting provided the necessary space and affordability for the project. Neighbours played a significant role in the decision-making process as well. They engaged with the community early to ensure a supportive environment. This holistic view of site selection goes beyond mere physical measurements. It considers the social and environmental context of the land.
Tri-generational living builds family resilience and financial viability
Two houses were to be built on the site with one home for Janna’s parents, fostering tri-generational living. This setup allows for mutual support as the family members age. Children benefit from closer relationships with grandparents during their upbringing. The project also became more viable financially because they were sharing land and build costs with the older generation. Overall the arrangement builds resilience within the immediate family network.
Design can actively support biodiversity and habitat creation
Biodiversity was not side-lined during the design process. A third of the roof space of Janna and Seb’s house is dedicated to habitats for birds and bats. Open soffits allow wildlife to access the eaves without obstruction. This design choice supports local ecosystems rather than excluding them. They have already observed various species investigating the roof space since the structure was finished.
When it came to choosing the right materials for the house build it was always with an eye on the end of the life cycle. They wanted to ensure they would not poison their immediate environment when the building comes to the end of its life (hopefully centuries into the future!). For example, most of the materials would break down over time and return to the earth. Every decision aims to have a positive impact on the surrounding habitat, which almost treats the building as part of the landscape.
Deconstruction preserves valuable materials for reuse
There was an existing cottage on the site which was beyond repair and rather than demolishing it they were keen to deconstruct it. This process allowed for the careful removal of reusable materials like slates and timber. Windows were reclaimed and repurposed for the solar panel array and potting shed. Even the gas boiler was traded with a neighbour for an e-bike. This method significantly reduced waste sent to landfill. They even uncovered valuable old oak which is no longer commercially available. Although all of this is slower, the extra time required was justified by the environmental and economic benefits. Janna and Seb believe this more sensible and responsible approach should become the default in the industry.
Adequate storage is important to protect reclaimed materials
Storing salvaged materials normally requires a large amount of space and somewhere close by. Janna and Seb already had a good-sized plot, 1.5 acres, and initially used a garden marquee to house the materials, but this did not survive the winter storms! Instead a Polytunnel provided a much more durable and practical option. Without a dry space like this, reclaimed items can quickly become unusable.
The builder had input into the construction approach
When considering what materials the house should be built from and looking at the construction method, Seb compliments Janna on keeping an open mind. Her approach was to allow a wide wall build-up, knowing that natural materials would require this, and then consider the different options and ask the builder how they would like to approach it. For example, they looked at EcoCocon straw panels but there were logistical challenges with getting the delivery to site. They also weighed up other timber approaches and straw bale building, but with Janna’s parents keen that the construction period didn’t drag on they eventually opted for a modular system that their builder was familiar with.
“We ended up with a builder who had a kind of in-house developed timber modular panelised system, which is a Larsen truss system, so two bits of timber, and then it’s held together with plywood gussets and then fully filled with warmcel insulation, airtightness line on the inside.” — Seb Laan Lomas
Screw pile foundations offer a low-carbon alternative to concrete
One of the aims of the project was to avoid poured concrete. Therefore they used a screw pile system that has a seventy per cent lower embodied carbon than traditional concrete slab foundations. Another benefit is that they are fully reusable and recyclable at the end of the building’s life. The contractor was impressed and found the whole approach easier and faster.
Once out of the ground they are using almost entirely natural materials. So there’s a timber floor which is raised above the ground to ensure airflow and prevent moisture issues.
“On the moisture front, whilst we know that these design principles are going to work, we have installed a whole range of moisture sensors throughout the building, and so they wirelessly transmit data from wherever they’ve been installed, of the moisture content and of every bit of wood they’re screwed into, as well as the temperature and the relative humidity at the sensor. So we’ve got them in the floor construction, we’ve got them throughout the wall construction, we’ve got them in the roof, and we’ve got some on some of the internal walls.” — Seb Laan Lomas
The sensors have shown the whole moisture journey of the building to date, and communicate and reassure everyone that this is a safe and resilient way to use natural materials.
It’s hard to eliminate plastics but you can certainly minimise their use
When you’re building a Passivhaus a common approach is to insulate with EPS beneath the slab. Janna and Seb have managed to avoid this because of their alternative foundation solution.
Plastics are also frequently used in airtightness layers, with products such as tapes and membranes. Again, Janna and Seb have thought hard about how they can keep plastic use to a minimum. In this instance they’re mainly using an airtight OSB (SmartPly) which only has a very thin layer of plastic.
“This whole process has opened my eyes to the quantity of plastic in the packaging, which includes the natural materials that we’ve so carefully chosen… It has been quite disheartening at times, you know, several skips worth of just packaging, which when we’ve tried so hard to minimise waste and minimise plastic in the build, and there’s far more plastic that went in the skip than there is that’s gone in the house.” — Janna Laan Lomas
The contractor delivered a watertight and airtight shell, allowing Seb and Janna to take over at first fix.
Volunteer labour has helped reduce plastering costs
After being quoted around £20,000 for plastering the inside of the house (which included materials and labour), Janna and Seb took a different approach. Over one hundred volunteers assisted with the plastering and finishing work. Participants ranged from architectural students to local homeowners and builders. With the clay coming from the existing site the cost savings were substantial compared to hiring professional plasterers. In fact the only outgoings were for food and drink to thank the volunteers for their time, which came to about £400. Another benefit of this approach was that it served as a training opportunity for those interested in natural materials.
Handmade finishes celebrate imperfection and natural beauty
The interior finish is a clay plaster (clay, sand and fibre) that is mixed together on site and applied to the walls. Its texture and feel adds warmth and character to the house while adding a couple of other useful characteristics. The clay plaster regulates humidity and contributes to thermal mass. When formulating the mix Janna experimented with using wood fibre dust to improve crack resilience and it worked a treat. Although time-consuming this approach produces a lovely finish that perfectly aligns with their natural home and is easily maintained in the coming years.
Getting Building Control sign-off can be challenging with natural materials
Using non-standard materials, even if traditional and age-old, presented challenges with getting building regulations approval for Part B (fire safety). Their Approved Inspector was unfamiliar with clay plaster performance data and would not sign it off because there was no data relating to the specific site and use in this instance. However, switching to Local Authority Building Control seemed to resolve the issue because they had had experience of people doing this before. Extensive research and test data were required to satisfy safety requirements. This experience highlights the need for inspectors to understand traditional techniques. So if you’re planning to go down this route, you need to find Approved Inspectors or Local Authority Building Control who are experienced with natural builds. Janna and Seb were a little unnerved by this, but were pleased to find a solution. Documentation is key to proving compliance with safety standards.
Spend money in the right places
Janna and Seb chose to allocate £20,000 to a specially commissioned oak staircase. Not only was this part of Janna’s original dream but it’s a permanent structural element that also defines the home. The design mimics a sweeping Georgian stone staircase but as it was to be built in timber there were a few design challenges. Close collaboration with the craftsman Carwyn Jones ensured the complex joinery accounted for wood movement without compromising the solid oak construction. This decision highlights their strategy of prioritising the building fabric over cosmetic details that can be changed in the future.
A low heat demand allowed them to simplify their heating strategy
Initially they had been looking at an air source heat pump to provide heating for the house. However, they found that it was really tricky to find a good designer and often the systems were way to large for their small heating requirements. The embodied carbon of the whole installation and the impacts of the refrigerant led them to look at other options. In the end they decided to install three 1kW direct electric heaters. This was much simpler and cheaper, and freed up cash to invest in solar PV panels and battery storage. It proves that a fabric-first approach can scale down your energy needs. Building to the Passivhaus standard is a tried and tested approach to delivering a healthy, comfortable and energy efficient dwelling.
Mark Lynn from Eden Renewable Innovations explains how sheep’s wool insulation is made, outlines the pros and cons, and suggests how it is best specified and installed. He also shares some common traits of natural fibre insulation as a category.
Interview with Mark Lynn
In this episode Ben Adam‑Smith sits down with Mark Lynn, Managing Director of Eden Renewable Innovations and Chair of the Alliance for Sustainable Building Products (ASBP). Together they unpack what natural‑fibre insulation really means, why sheep’s wool insulation is gaining traction, and what homeowners and builders need to keep in mind when specifying and installing products such as Thermafleece.
Natural fibre insulation is any building insulation made from renewable plant or animal fibres
Mark defines natural‑fibre insulation as any product whose primary component comes from a biological source – sheep’s wool, wood fibre, hemp, jute, cotton, flax and cellulose are just some examples. These materials can be used alone or blended, and they are often processed into batts, rolls, rigid boards, or loose‑fill. Because the raw element is renewable, the embodied carbon of the product is typically far lower than that of conventional mineral or synthetic insulation.
“Natural fibre insulation is any building insulation that’s made from or using natural fibres.”
The variety of fibres gives designers flexibility: wood fibre offers rigidity, hemp provides high tensile strength, while wool excels at moisture regulation. Understanding the source material helps you match the product to the building’s performance goals.
Moisture‑buffering is a unique strength of natural fibres
At the molecular level, natural fibres carry electrical charges that attract water molecules. Rather than allowing water to pool as a liquid, the fibres hold it in a solid‑state “bound” condition. This limits the risk of mould and rot, because the water cannot act as a universal solvent that accelerates decay.
Sheep’s wool, composed of the protein keratin, is especially adept at this exchange, absorbing humidity when the indoor air is damp and releasing it when conditions dry out. The result is a more stable indoor environment, particularly in climates where indoor humidity fluctuates dramatically.
“When the water molecules adhere to the natural fibre the way they do, they can’t behave like a liquid.”
Breathability is not a substitute for ventilation
Mark cautions that a breathable fabric does not eliminate the need for a proper ventilation strategy. Inside our homes we generate moisture through our activities (showering, cooking, doing laundry, etc.) so there needs to be a constant exchange of stale air being replaced with fresh air. In Passivhaus homes, for example, mechanical ventilation with heat recovery (MVHR) fulfils this role. The insulation’s ability to buffer humidity is therefore an additional benefit rather than an excuse to forget about ventilation.
Good design requires adequate ventilation, sufficient vapour openness (the ability of water vapour to pass through the material), and the inherent moisture‑buffering capacity of the fibre. When these work together, the insulation remains effective without becoming saturated.
Condensation risks can be modelled
Tools such as WUFI can help model moisture, taking into account climate data, wall build-ups, and internal conditions. This will then identify potential condensation risks and allow them to be addressed at the design stage. Ignoring this step can lead to interstitial condensation and the knock-on effects of mould and damp, which in severe cases could even cause structural damage.
Three main forms of natural‑fibre insulation: flexible, rigid, and loose‑fill
Flexible insulation – often supplied in slabs, batts or rolls that can be cut to size.
Rigid wood‑fibre boards – medium‑density panels that can be fixed to walls or roofs, offering structural support.
Loose‑fill – shredded fibres (typically recycled newspaper or fine wood) blown into cavities, ideal for irregular spaces.
Sheep’s wool is available both as flexible batts and as rolls, giving installers the convenience of a rockwool‑style product while retaining the natural advantages of wool.
Sheep’s wool insulation is easy to install in a loft
We should be taking advantage of all natural fibre insulations
When asked about how we choose a natural fibre insulation, Mark suggests that it’s actually better to support the whole category. All natural fibre insulations will have their strengths. For example, when insulating a loft a roll of sheep’s wool may be the simplest and quickest to install.
“We’ve got to use the right type of the right resource in the right way, and that really involves a whole mix of materials.”
The ASBP’s Natural Fibre Insulation Group publishes a comparative guide that helps architects weigh factors such as thermal performance, acoustic qualities, fire resistance, and cost. Using that data ensures the selected material aligns with the building’s functional and regulatory needs.
The market for natural‑fibre insulation is growing
Historically, natural fibres accounted for roughly 1 % of the UK insulation market, compared with 10–15 % in France and Germany. Since the pandemic, consumer research into health‑focused homes has accelerated adoption, and manufacturers report strong year‑on‑year growth.
Mark predicts that reaching the 10–15 % threshold in the UK would make natural fibres a credible mainstream option, offering homeowners greater choice without sacrificing performance.
“These aren’t quirky eco products, they are part of the insulation mix.”
Shearing a sheep for its wool
Manufacturing sheep’s wool insulation
Sheep’s wool delivers acoustic performance comparable to high‑grade rockwool
Thermafleece UltraWool, a flagship wool product, achieves the same sound‑absorption ratings as a 45 kg/m³ rockwool product, despite being only 32 kg/m³. The lower density reduces dead‑load on the structure while still dampening noise, making it a compelling option for residential lofts and office partitions where acoustic comfort is a priority.
Fire safety is addressed through mineral fire retardants, not by claiming non‑combustibility
All natural‑fibre products, including wool, incorporate a mineral fire retardant that encourages charring rather than rapid flame spread. While they are not classified as “non‑combustible,” they meet Part B of the Building Regulations for the intended applications.
For projects that require a non‑combustible rating—such as certain high‑rise or public‑access buildings—additional layers or alternative materials may still be necessary.
Insulating a barn with sheep’s wool insulation
Cost is competitive when viewed against performance and lifespan
Mark notes that comparing wool to a cheap fiberglass roll can be misleading. When matched against high‑performance mineral products, the price differential narrows, especially when accounting for its long life (60 + years) and the reduced need for replacement.
A typical loft installation with Thermafleece can be completed for under £1,000, and the energy savings often recoup the investment within five years.
A thin layer of insulation can make a big impact
When dealing with existing buildings, for example a period property with a solid wall, a thin layer of internal insulation can make a big impact to comfort and keep costs down. It must however be a continuous layer, eliminate thermal bridges and be installed well. One advantage of this thin layer is that you’re far less likely to have moisture build-up in the fabric, but you’ll feel a noticeable benefit to the comfort of the property.
Environmental benefits extend beyond the insulation itself
Sheep’s wool used in insulation is often sourced from the coarse, dark fleece that has limited textile applications, turning an agricultural waste stream into a high‑value building product. The polyester binder incorporated into the rolls is made from recycled plastic bottles, further closing the material loop.
By sequestering carbon in the keratin fibres and reducing the demand for petrochemical‑based insulation, wool contributes to lower embodied emissions and supports rural economies.
“We’re buying a reasonable proportion of the UK wool clip… adding value to the rural economy.”
Mark Doodes from Mark Doodes Planning explains what we mean by applying for planning permission to demolish and rebuild a house, how it is done, what some of the challenges might be and how to do as much as possible to improve your chances of a successful outcome.
Interview with Mark Doodes
Mark Doodes is a chartered member of the Royal Town Planning Institute and the founder of Mark Doodes Planning. After starting his career in local‑authority planning and working on e‑planning projects during the early 2000s, he moved into private practice and, twelve years ago, set up his own consultancy. Mark combines public‑sector insight with private‑practice pragmatism, helping self‑builders and developers navigate the often‑confusing maze of UK planning policy. His experience ranges from small rural bungalow replacements to large housing‑scheme negotiations, and he is known for a clear, step‑by‑step approach that keeps clients realistic about timelines, costs, and risks.
The planning system is a patchwork of legislation and policy
Planning in England draws on national statutes, secondary regulations, local plans, neighbourhood plans, case law and appeal decisions. Each of these layers interacts to guide a planning officer toward either approval or refusal. Because the system pulls together many sources, it may sometimes seem confusing to newcomers. Understanding which document carries the most weight for a particular site helps focus efforts and avoids chasing dead‑ends. As Mark puts it, “the planning system is actually quite difficult to define and very difficult for neophytes to navigate.”
Local plans dictate where development can happen
Local plans are the primary tool councils use to allocate land for housing, industry, commerce and other uses after years of consultation and evidence gathering. These allocations are the first checkpoint for any planning proposal. Mark says that sometimes these plans will be out of date, which can add in another layer of complexity.
Neighbourhood plans add a hyper‑local layer
Neighbourhood plans are drafted by communities and can refine the broader local plan for a village or suburb. They may set limits on the number of new homes, design standards, or specific constraints such as preserving the character of a village. Because they sit below the local plan, they can introduce additional hurdles—or opportunities—that are invisible on a county‑wide map. A quick glance at the neighbourhood plan can reveal hidden constraints before a formal application is submitted.
Replacement‑dwelling policies vary between councils
Each council publishes its own guidance on how much larger a new house can be compared with the one it replaces. The wording is not prescriptive which gives decision‑makers some flexibility. This means applicants must negotiate with the council and demonstrate why a modest increase is justified.
Exercising permitted development rights can help you
Many small alterations—side extensions, dormer windows, raising the roofline—fall under Class AA or other permitted‑development rights. Before drafting a full planning application, it pays to map out what can be done without consent. Using these rights wisely can shrink the scale of the formal proposal, improving the odds of acceptance and saving time and money.
Staged approaches smooth the path to larger schemes
Rather than applying for a dramatically larger dwelling in one go, breaking the project into incremental steps (e.g., first getting permission for an extension before returning with another application) often yields better outcomes. Each stage is judged against its own impact, and the cumulative effect can eventually reach the desired size or the approvals gained can be used to negotiate.
“Going A → B → C → D has a much higher chance than jumping straight to D.”
In most negotiations both parties stand to gain something, but as Mark points out, a planning officer may be relatively ambivalent to the outcome, just wanting the case to be concluded.
Some ecological surveys have to be carried out at specific times
Ecological surveys for bats, great‑crested newts and other protected species are bound to specific windows (bats May‑September, newts March‑June). Missing these periods forces delays and can push a planning schedule back by months. Early engagement with specialists ensures that required evidence arrives in time for the application, keeping the project on track.
Outline planning permission offers flexibility with reduced paperwork
Submitting an outline application secures the principle of development without committing to detailed designs. This can be advantageous when the exact layout is still evolving or when you want to establish if a consent will be given. The outline still requires supporting reports—transport, drainage, ecology—and is recorded publicly, creating a tradable asset that can be sold or transferred.
Avoid short-term financing if waiting for a planning decision
Planning timelines can stretch well beyond optimistic estimates—often 12–16 weeks for a decision, plus additional weeks for appeals if needed. So relying on short-term financing based on a promised approval can be asking for trouble and expose you to high interest if the process stalls. Mark has seen this crop up too many times before and therefore he would always advise against using bridging loans.
Planning permission is valid for three years
Once a full planning permission is granted, the applicant has three years to commence development. There is no statutory deadline for completion, though prolonged inactivity may trigger Section 215 powers to clean up an abandoned site. Most owners start work well before the three‑year limit and are keen to get on with their projects.
Give the planners all the information they need
If there is any doubt about a particular aspect of the application it is wise to preempt requests for further information by producing the relevant report ahead of time. These might include ecological reports, drainage calculations, heritage assessments, and transport impact studies, etc. Missing these can stall the process or invite objections. Providing a well‑organised application demonstrates professionalism and reduces the likelihood of back‑and‑forth queries, increasing the chance of a smooth decision.
“Nobody gets the end of the process and says, gosh, that UK planning system was so predictable, inexpensive and consistent. No one says that! So allow plenty of time, plan for the worst case scenario.”
Be aware that policies can change
National policies such as the National Planning Policy Framework (NPPF) are updated roughly every year. A local plan that was favourable when an application was lodged may be re‑tested against a newer national framework, altering the weighting of criteria. Keeping an eye on upcoming policy revisions helps anticipate potential shifts that could affect a pending case.
Dr. James Glockling explains how insurance works and outlines some of the challenges of insuring a natural building.
Interview with Dr. James Glockling
Dr. James Glockling began his career with the Loss Prevention Council, the insurers’ hub for studying fire, security, flood and other loss‑mitigation challenges. He later deepened his expertise at the Building Research Establishment (BRE), and then worked at the Fire Protection Association before setting out on his own as a consultant. His clients are wide-ranging, including insurers and even the military, helping them build resilience and mitigate risks in high‑risk scenarios—from multi-storey apartment blocks to the confines of a submarine. His work reminds us that, regardless of setting, safety rests on the same timeless principle: robust materials and well‑designed systems protect the people who depend on them.
In this podcast interview we discuss everything from one-off homes to high-rise, multi-dwelling projects.
Insurance protects the individual against disaster
Insurance began as a collective safety net, allowing many people to share the cost of rare but catastrophic events. By pooling premiums, an insurer can compensate an individual when a loss occurs, turning an unpredictable disaster into a manageable financial outcome. This principle still underpins modern home and commercial policies, even as building practices evolve. Understanding insurance as a partnership rather than a pure expense helps homeowners see it as part of responsible building.
“Insurance was originally set up as a means of protecting people against disaster, where you levy a premium on a large group of people to protect the interests of the individual.”
Insurers have to weigh up a variety of risks
Underwriters assess far more than fire. They examine the building’s use, size, occupancy, and any ancillary systems such as solar panels, battery storage, EV chargers, green roofs, or underground car parks. Factors like these may have an impact, so insurers request detailed information on design, materials and mitigation measures. The broader the picture they have, the more accurately they can price a policy and set conditions.
One-off homes should be easier to insure
As insurers always have to think about a complete loss and rebuild, having a single smaller property is a limited loss scenario. As the scale of a building increases so does the potential loss scenario.
Estimated Maximum Loss (EML) is a key metric for insurers
EML is the insurer’s worst‑case estimate of loss from a single incident, expressed as a proportion of the building’s total value. For a 20‑storey tower, an insurer might assume only four floors could be completely destroyed, translating to a 20 % EML. When new construction methods make fire spread more unpredictable, insurers often raise the EML toward 100 %, which drives premiums skyward or leads to outright refusal. Demonstrating a defensible, lower EML is therefore a key part of the underwriting conversation.
Under‑insuring is a false economy
Many owners underestimate the true rebuild cost of their property, declaring a lower value to obtain cheaper premiums. If a total loss occurs, the payout will only cover the declared amount, leaving owners with a significant funding gap. Accurate valuation, combined with robust risk mitigation, ensures that the insurance policy truly protects the investment.
Insurance companies may have their own specialist areas
James says that he used to live in a thatched home and that his monthly insurance premium was what most people would pay for a year. This is because if a thatched roof catches fire then the house will be a complete loss. However, NFU Mutual have made this their specialism and are seen as the go-to provider. This is because they understand the risks, know what conditions matter and have a history in this area.
Water damage is the most common insurance claim
Water loss accounts for billions of pounds of damage each year and occurs far more frequently than fire. Burst pipes, roof leaks and flood ingress can rapidly degrade timber, leading to rot, mould and structural failure. Early detection systems—wireless tape sensors, automatic shut‑offs—are increasingly expected by insurers, especially for mass timber projects where hidden water would otherwise go unnoticed for months. Proactive monitoring can therefore reduce both risk and premium.
When it comes to timber, voids present a fire risk
As timber is combustible, the design of a building becomes crucial. Voids can allow smoke, heat, and flames to spread rapidly, bypassing sprinklers and complicating firefighter access. Mass‑timber panels (CLT, glulam) reduce voids but may be subject to smouldering, which can persist for many hours and even lead to the flames reigniting. These behaviours force insurers to demand rigorous fire‑stopping, compartmentation, and sometimes hybrid designs to keep the EML manageable.
It’s essential that fire‑stopping is correctly installed
Every penetration—pipes, ducts, cables—in walls and floors must be sealed with a fire‑stopping material. Missing or poorly installed fire stops create pathways for flames and smoke, dramatically increasing the EML. In light‑timber frames, the sheer number of voids makes comprehensive fire‑stop inspection essential. Regular audits, preferably by a dedicated Clerk of Works, provide the documentary evidence insurers demand. This may make a boring photo collection but it will be a valuable one.
“I haven’t been to any fire in a building where I haven’t found the fire-stopping either missing or misplaced or just absent.”
Hybrid designs with concrete cores satisfy insurers
In high-rise buildings, combining timber with non‑combustible elements—concrete cores, steel columns or concrete plinths—offers insurers a tangible safety buffer. A concrete core protects against fire spread, provides a stable fire‑fighter access route, and serves as a flood‑resistant base. Such hybrids offer the best of both worlds, with the carbon benefits of timber while delivering the structural and fire‑performance assurances underwriters look for.
Take photos during construction to provide evidence of good workmanship
Even the best design fails without quality construction. Insurers scrutinise records of on‑site inspections, photographs and sign‑offs to confirm that fire‑stops, penetrations and material installations match the approved design. A diligent Clerk of Works creates a paper trail that can be presented during underwriting and later claims, reducing disputes and speeding up payouts.
“Evidence is everything, and if there’s a Clerk of Works properly reporting on the job as it’s put together, then that can only be of great benefit.”
Insurers steer away from complexity
The industry uses six categories to describe the percentage of combustible material in a building. For example, Structural‑Insulated Panels (SIPs) are often highly combustible, pushing a project into the highest risk tier. When a building lands in the 100 % combustible category, insurers typically raise premiums sharply or decline coverage. Understanding these categories lets designers choose lower‑risk assemblies or offset risk with non‑combustible cores.
The Mass Timber Insurance Playbook is useful resource
The Mass Timber Insurance Playbook, co‑authored by Dr. Glockling and broker Philip Callow, lists 26 features that insurers evaluate in timber projects and offers practical mitigation strategies. It is freely downloadable from the Alliance for Sustainable Building Products website and provides a clear roadmap for architects, engineers and developers.
Increasingly AI is being used in the underwriting process
Insurers are increasingly using artificial intelligence to analyse loss data, identify patterns and refine risk models. By feeding detailed, high‑quality information from the construction phase into these systems, builders can help shape more favourable underwriting outcomes in the future.
Hugh Franklin from Aeroseal UK explains how the airtightness of a building can be improved using a water-based, low VOC atomised polymer which is delivered when the building is pressurised. This simpler approach speeds up the process of air sealing and gives real-time feedback on the airtightness score.
Interview with Hugh Franklin
Hugh Franklin is the Head of Operations at Aeroseal UK, where he leads the development and deployment of the AeroBarrier airtightness system. His career began in archaeology, spending years de‑constructing historic buildings and extracting lessons about passive cooling, solar shading and other age-old strategies. Those insights sparked a shift toward eco‑construction, where he focused on scaling sustainable building practices before narrowing his expertise to airtightness over the past eight years. Today, Hugh combines his deep appreciation for traditional building wisdom with the latest technology to help builders achieve high performance homes.
The ‘mist’ sealant automatically hones in on the leaks
Airtightness is a key characteristic of a high performance home, but airtightness strategies can be labour‑intensive using boards, membranes, tapes, liquid paints and so on. Hugh describes how a mist of low‑VOC polymer sealant, delivered under pressure, automatically seeks out leaks and creates a uniform seal. This reduces material waste, shortens installation time, and delivers measurable improvements in the building’s air‑leakage score.
“We create a fog, a mist of a water-based low-VOC sealant… the sealant is drawn towards those leaks by the escaping air.”
It is possible to dial‑in the airtightness you want
AeroBarrier is introduced into a building during a standard blower‑door test. When the building is pressurised the mist travels through any gap or crack, collides with itself and solidifies around the leak. Because the product is an acrylic polymer that is 60–80 % water, only a few litres are needed for a typical 200 m² home. The sealant does not expand; it accumulates only where airflow exists, allowing the airtightness score to be dialled down to the exact target.
The building is carefully controlled during misting
Everyone steps outside while the mist is applied and it doesn’t take long. Workers inside wear appropriate respiratory protection, but the low‑VOC formulation produces minimal fumes. After sealing, the space can be re‑entered within 30–60 minutes once the mist has dried, making the process practical for busy construction sites.
“We control the space during the install, much like if you’re doing an airtightness test.”
Long‑term durability is proven in the lab and the field
AeroBarrier has undergone lab testing up to 5 000 Pascals (hurricane‑level pressure) and shows no degradation after 50 years of simulated ageing. Field studies report only a 1–2 % loss of airtightness over 25 years, confirming that the polymer remains flexible and effective long after installation.
Automation works best when paired with manual detailing
The system can seal gaps up to 10 mm. Larger openings generate a visible “white halo” during misting, signalling that manual patching is required. This hybrid approach lets builders concentrate on the biggest defects while AeroBarrier handles the multitude of smaller, hard‑to‑detect leaks.
“AeroBarrier will try and seal that, but it will start to form a white halo around a hole that’s quite large… you can walk around the building… and find those gaps and then fill them manually.”
Real‑time feedback turns airtightness into a visible metric
A key obstacle in airtightness is the lack of instant performance data. AeroBarrier integrates with the blower‑door test, displaying the current ACH (air changes per hour) score on a screen as the mist seals each leak. This immediate feedback lets site teams see which details are performing well and which need attention, fostering ongoing learning and improvement.
There is an optimal moment to apply the sealant
For new builds, the best time to apply the mist is post‑first‑fix, after windows, glazing and major services are installed but before interior finishes. In retrofits, the building must be sufficiently sealed to become a “pressurisable box”; otherwise, the mist will escape and the process loses efficiency. Coordinating with the contractor to schedule the test at the right stage is essential for success.
“We want the building to look as much like a porcupine as possible. Post first fix is really when we want to come in.”
A draught-free home will deliver savings
AeroBarrier is priced at roughly £12.50 per square metre of floor area. For a 200 m² home, material costs are about £2 500, plus labour. Hugh notes that the return on investment typically appears within three to five years through reduced heating and cooling demand, especially when moving from a standard Building Regulations home to the Passivhaus standard.
Achieving airtightness this way requires a slightly different plan
Hugh says that their best clients keep an open mind about the approach to airtightness. It’s much better to have a talk upfront about how to get the most out of the system. For example, setting clear tolerances early on will avoid unnecessary work (e.g., keep penetrations ≤ 5 mm for high‑performance builds). Builders, plumbers, electricians and ventilation suppliers need to understand these limits and coordinate their work to avoid unintentionally creating new leaks. Brief on‑site training and visual guides help keep everyone aligned.
Once achieved, airtightness must be preserved
If a great airtightness result is achieved at first fix this is not a cue to rest on your laurels. Throughout the project it’s important that everyone who is working on site understands the airtightness line. Typical mistakes might include cutting through an airtight membrane without making good afterwards. Hugh shares a couple of examples. When electricians are installing recessed lighting they might not quite have enough room so they cut through the membrane. Also when it comes to adding services, like cables, pipes and ducting, a similar problem can occur. Because the airtight layer is often invisible, any breach can dramatically reduce the airtightness of a property. Scheduling blower‑door tests at key points and encouraging a culture that reports issues without blame can help maintain a good airtightness score.
Scaling airtightness for mass‑market housing
Hugh believes that making airtightness cheap, fast and easy to verify is the key to bringing low‑energy homes to the broader market. By combining automated sealing with clear performance metrics, builders can deliver consistent results without needing specialist airtightness gurus on every site. The goal is to demystify airtightness, turning it from “black magic” into a routine part of construction.
Elly Deacon Smith and Kirk Rushby from Arbor Architects explain why they consider the embodied carbon of their projects, how they do it and how it is balanced with competing factors.
Interview with Elly Deacon Smith and Kirk Rushby
Elly Deacon Smith is the Founding Director of Arbor Architects with nearly 25 years of experience. She began her career in Bristol at White Design, working on straw and timber projects that emphasised both embodied and operational carbon long before it became mainstream. After moving back to Herefordshire, she joined Architype, deepening her expertise in Passivhaus construction and building physics, before co‑founding Arbor Architects, which she now leads.
Kirk Rushby is an Associate at Arbor Architects with roughly 20 years in the field, fifteen of which were spent at Architype. His background mirrors Elly’s focus on sustainable, low‑energy design and bio‑based materials. He’s also built his own Passivhaus home.
Focusing only on the energy a building uses in operation misses a large portion of its climate impact. Embodied carbon covers emissions from material extraction, manufacture, transport, construction and demolition. Even a Passivhaus can carry a substantial carbon debt if high‑impact materials are used. Measuring both sides lets designers keep total lifetime emissions within targets like the RIBA 2030 benchmark.
“We’re aware that operational carbon is regulated, but embodied carbon is a bigger blind spot,” Elly notes.
Make sure your design team is carbon literate
Elly taught a master’s course at the Welsh School of Architecture. A key aspect she encouraged was to “think in carbon” for every decision. This habit makes it easier to spot high‑impact choices later, because the designer already asks, “What is the carbon cost of this material?” Kirk agrees that years of practice have turned this questioning into second nature. Early education therefore lays the groundwork for systematic carbon reduction and intuitive decisions.
Use specialist tools to quantify embodied carbon
Arbor initially hired an external consultant to run assessments in PH Ribbon, which can use a certain amount of information from the existing PHPP model. The consultant just required quantities for elements like walls, floors and roofs, enabling calculation of kilograms of CO₂ per square metre. More recently Kirk is using a tool from Studio Bark, whose emerging calculator pulls volumes directly from Revit models, delivering near‑instant feedback.
“We’re really keen to be able to model in‑house, and to be able to make decisions quite quickly,” Elly explains.
Tin Barn
Take advantage of real‑world case studies
Arbor’s retrofitted Tin Barn (certified to the EnerPHit standard) achieved about 347 kg CO₂ / m², comfortably below the RIBA 2030 target. By contrast, a newly built garden‑room annex with timber framing and zinc cladding recorded just over 600 kg CO₂ / m². Interestingly, adding a photovoltaic array increased the figure by roughly 100 kg CO₂ / m². Elly says that this is another good reason to take a fabric first approach so that you keep your energy needs to a minimum.
Cwm Barn
Test assumptions: zinc cladding may not increase carbon dramatically
Swapping timber cladding for zinc on the Cwm Barn garden‑room added only a modest amount of embodied carbon, perhaps contrary to expectations. Elly attributes this to the relatively small surface area and the fact that the underlying timber structure already contributed most of the carbon.
“One of the surprises was that the decision to clad the garden room in zinc didn’t have as big an impact as we thought,” Elly comments.
So the lesson is to evaluate material impact in context rather than doing it intuitively.
Quick checks, early in the design process, make it possible to consider embodied carbon for every project
Waiting weeks for external consultants slows down design decisions and is not practical in the long run. So using a simpler embodied carbon tool like the one from Studio Bark means the whole process becomes easier, different options can be evaluated and it can be integrated into the standard workflow.
Using bio‑based materials normally leads to a good carbon outcome
As a general rule at Arbor they like to build with timber. This stores carbon from the tree’s growth, giving it a lower embodied carbon compared to other methods of construction.
Recognise foundations and substructure as the biggest carbon hotspot
Concrete foundations are inherently carbon‑intensive and often difficult to get away from. However, you can reduce volumes with good design or use low‑carbon mixes. Sometimes screw piles can be a way to avoid concrete altogether but these will normally be made of steel which again has a high embodied carbon. That said, they can be removed and reused at the end of the life cycle.
Balance cost, client expectations and carbon goals early on
High‑performance homes and Passivhaus certification typically increase material quantities and costs a little. Arbor addresses this by being transparent with clients from the outset about trade‑offs between carbon performance and budget. Early budgeting conversations help align expectations, and designers explore “more with less” tactics—optimising layout, trimming unnecessary floor area, and selecting durable, low‑maintenance finishes that lower lifecycle costs. Kirk stresses that “you can get more out of less” with the right mentality.
Good decision-making considers many factors
Embodied carbon is just one aspect of a sustainable home. Arbor evaluates each material for moisture handling, indoor air quality contribution, longevity and visual ageing.
Designer experience and instinct are still important
For design teams that aren’t yet modelling embodied carbon, logical decisions can often lead to low carbon outcomes: prioritise low‑impact substructures, favour timber over masonry where feasible, reuse on‑site materials, and keep use of steel to a minimum.
Anticipate a future where measurement is seamless and data is shared
Whereas many design teams are familiar with operational carbon, the future could see quick‑feedback calculators embedded in standard workflows and a shared database of embodied‑carbon benchmarks for common building typologies. More data will enable designers to make confident, low‑carbon decisions early in the design process, accelerating the transition to a net‑zero built environment.
Marion Baeli, author of “Residential Retrofit,” offers hands-on experience of designing and retrofitting high performance homes. As well as drawing on her personal retrofit she shares the lessons learnt from revisiting properties that took part in the Retrofit for the Future competition over a decade ago.
Interview with Marion Baeli
Marion Baeli is Principal, Sustainability Transformation at 10 Design and author of “Residential Retrofit,” covering the evolution of retrofitting over the past decade. Originally a French architect, Marion came to the UK in 2002 and later took a master’s degree in sustainable architecture and design. This brought a fundamental shift in her approach so that she now embraces the Passivhaus methodology, and considers all aspects of embodied carbon and material circularity in her work.
She was fortunate to be part of the Retrofit for the Future competition and has been able to revisit several of the properties, ten years later to assess their performance. She also draws on the experience of her personal retrofit project to highlight the differences between good and bad retrofits.
Retrofit needs a holistic, system‑level approach
Marion stresses that many retrofit failures stem from treating the building as a collection of isolated fixes. She points out that focusing solely on insulation, without addressing moisture control, ventilation, airtightness, and thermal bridges, inevitably creates new problems. A coordinated design that balances all performance factors is essential for long‑term durability. This mindset is now embedded in standards such as PAS 2035, which require a comprehensive retrofit plan before work begins.
“You can’t really do a retrofit by looking at just one thing… you need a holistic approach.”
Start with thorough planning and expert co-ordination
For Marion the most reliable retrofits begin with careful upfront planning, bringing together architects, engineers, contractors, and a retrofit coordinator to ensure that each intervention is contributing to the overall performance target. Marion recounts that the original “Retrofit for the Future” case studies succeeded because the teams invested heavily in design time, avoiding costly re‑work later. Skipping this step often leads to unintended consequences and poor performance.
Long‑term performance holds up when quality is built in
When revisiting a number of the original case studies that featured in the book and carrying out building performance evaluation, Marion reports that airtightness, insulation integrity, and thermal bridge mitigation have largely remained intact. No major failures such as tape peeling or board collapse were observed, confirming that a well‑executed retrofit can be long-lasting. The key takeaway is that investing time and expertise at the start pays dividends in sustained performance and lower operating costs.
Watch our in-depth video case study of the Kinver retrofit in The Hub.
Regular maintenance of the building fabric is essential
Even the best‑designed retrofit can be undermined by neglected maintenance (which is obviously nothing to do with retrofit). Marion cites a case where a leaky gutter caused brickwork to spoil and moss growth which could have threatened the structural longevity. Simple upkeep, cleaning gutters, repairing cracks, and checking flashing helps preserve the gains achieved through retrofit.
Window and door seals degrade over time
One common observation of the post occupancy evaluation was that gaskets around windows and doors have begun to lose elasticity, potentially starting to compromise airtightness. Although these can’t simply be replaced at the moment Marion believes we should all be raising this concern with our window manufacturers. She explains that on bigger projects and social housing they develop relationships with these suppliers and so units might be removed, repaired and replaced. This circular approach is needed for one-off homes too.
Financing retrofit needs to look beyond ROI
Marion argues that retrofit is not about return on investment. She likens it to buying and maintaining cars; you don’t expect a return on your investment when you buy a car and you maintain your car to ensure its safety and longevity. In many cases, the key benefits of retrofit are reduced energy bills, improved comfort and health, along with future‑proofing against climate change. Creative financing, phased implementation, and leveraging grants can make the upfront cost manageable.
Marion bought a mid terrace home with a plan to retrofit it
The plan and timelime of the step-by-step retrofit
Step‑by‑step retrofitting can be a good way to spread out the costs
Rather than tackling the whole house at once, Marion describes the phased strategy that she adopted. This involved making changes to the internal layout first as well as installing ground floor insulation and the ducting for the MVHR. Later she was able to address the external façade and windows, making sure that the house maintained its integrity with the other 1960’s houses on the estate. This allowed her to spread the costs over several years, while still moving into the house after the first phase. Planning each stage to dovetail with the next ensures that interim works do not compromise later performance targets.
“We’ve spent a lot of time planning the ductwork route – that’s the most difficult part of a retrofit.”
Significant construction work is better in one hit
Marion contrasts two approaches to construction disruption; to fully vacate the property for intensive works versus a staged, live‑in alternative. Her own project required a temporary relocation for six months, but she notes that many retrofits can be completed incrementally, allowing occupants to remain on site, perhaps moving around the house as the work is carried out. Choosing the right strategy depends on the building’s condition, the scope of work, and your personal tolerance for inconvenience!
A retrofit is often the time to look for other opportunities to make the building better
While carrying out the internal work, Marion added a light well to bring natural daylight into the core of the house, reducing reliance on artificial lighting. They also created bespoke timber storage units in the entrance hall and living area. In the summer months they are ready for a heatwave and have a pop-up fabric that they can stretch across the windows. Though simple DIY, this method effectively cuts solar gains, keeping the interior temperatures comfortable.
Passivhaus Open Days allow you to understand more about low energy homes
Ben and Marion are both big fans of the ‘Passivhaus Open Days’ event, which enables you to step inside completed Passivhaus or EnerPHit projects. This is a great way to experience the indoor environment and meet homeowners or professionals who have been involved.
“I’d encourage you to take advantage of these events… you can just make up your own mind.”
