Living proof

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Method: Timber frame, screw piles, bio-based materials, heat pump
Location: Dundee
Standard: Passive house classic
Heating cost: £20 per month space heating cost, between two households.
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The many projects I have covered in my 15 years writing for Passive House Plus share certain traits in common: extremely low energy use, airtightness, technical innovation, and rigorous attention to detail. Many were also low in embodied carbon, or prioritised bio-based and natural materials.

But every so often a project comes along that goes beyond technical and environmental ambition, to ask deep questions about how we use buildings, and reimagine how this relationship might look.

So it is with The Seed, a new passive house on the edge of Dundee which picked up the Supreme Award and Best New Home Award at the Dundee Institute of Architects 2023.

Built with a timber frame that is insulated with cellulose, and almost completely shunning the use of cement and concrete, the house is designed to be lived in by two families.

There was a really interesting discussion exploring a way for two families to live together.

The project was the vision of Karoline Hardt, who is from Germany but studied at St Andrews, before moving to Leeds, where she became inspired by the city’s cohousing developments. Cohousing is a form of intentional community, where people have private living quarters but share facilities such as guest bedrooms, gardens, laundry, even cars. A space for shared meals is common too, though homes generally have private kitchens as well.

When Karoline started looking to buy a home of her own, she wanted to take these principles and apply them to a smaller project, to create a home and garden that could be shared by two families.

“I read a lot of cohousing literature and case studies, mostly from Scandinavia,” she says. “But this was going to be something very different — how do you translate the principles of cohousing projects of 30 to 50 households, plus one common house, into a project of one house for two families? That was really tricky.” Her initial motivation was to reduce consumption and share resources – the washing machine, the hoover, simple things. “All the cohousing people I knew in Leeds were ecologically minded,” she says.

A big garden to grow food and make space for nature was integral to her vision, but it was hard to find a house with a decent sized garden within her budget in Glasgow, where she was living. So, she cast her eye further afield, and eventually bought a 1950s house with a one-acre garden on the western edge of Dundee. “Under the floorboards, there was 50 cm of air, then the soil. It was dusty and damp. I can’t believe I lived there for three years, it was very unhealthy,” she says.

Initially, the plan was for a deep retrofit. Karoline was interested in passive house, having been familiar with the concept from Germany, and she found Kirsty Maguire Architects (KMA), who specialise in passive house design and are based just across the Firth of Tay, in Newport-on-Tay.

Kirsty and Karoline looked at ways to upgrade the house, but the changes Karoline envisaged were significant, and the building was in such a poor state of repair that it would have been hard to retain much of the existing house. So, they made the decision to knock and rebuild.

Of course, demolish-and-rebuild usually results in a higher carbon footprint than retrofit. But it did give Karoline the opportunity to develop a purpose-built dwelling that is quite unique, being designed as it is around the concept of sharing resources.

“The ecological impact of renovation would have been smaller,” Karoline says, “but I think in this case it maybe was acceptable to build from scratch, because it allowed us to have our two families together, side by side.”

The finished house features a mix of private and communal spaces. Downstairs, the dwelling is divided in half, with two separate kitchen-and-living spaces, each with a sliding timber door that leads out to the communal, central hallway.

One of these kitchen-and-living spaces is for Karoline and her partner Carolina, while the other is for their friend Daniel and his daughter Emilia, who they share the house with. Between them, the two families have developed a simple language for communicating whether they would like to socialise or not. A fully open sliding door means, ‘we would love you to come in’. A closed door is a request for a privacy. A half-open door says, ‘come in if you would like to’.

The broad and bright communal hallway was designed as a meeting place and social hub. It has built in seating, and a covered porch at one end that is pleasant for sitting out on mild days. “We might all meet in the hallway and then start talking, so we end up hanging out in the hallway,” Karoline says. The back section of the house, which faces north, is just one-storey. It has a shared office that can double as a guest bedroom — a material and carbon efficient use of space — plus a sauna, accessed from the rear deck of the house, and a shower room. Upstairs there are three bedrooms, a washroom and shower room.

Outside, the garden is bordered on all sides by mature trees — beeches, Scots pines, birches, black poplars, ash, spruce, and Norway maple. In fact, the entire garden is covered by a tree preservation order. So many tree roots snake across the site that it restricted the area in which the new house could be built.

We might all meet in the hallway and start talking, so we end up hanging out in the hallway.

From the outset, the residents of The Seed set about creating an edible forest garden, applying the principles of permaculture. They have planted apple trees, pears, plums, cherries, hazels and chestnuts. They have also put in vegetable beds and have plans to build a greenhouse with windows salvaged from the old house, and to create a swimming pond, for people and wildlife.

They have given space to a local woman to keep bees, while Daniel, who home-educates his daughter, participates in a weekly meet up that Karoline hosts for home-educating parents and their children, who use the outdoor space to learn new skills and play in nature.

“The children are helping to design the garden,” Karoline says. “Their design brief is to make the garden more playful. Our big project this year is building the treehouses that the children asked for and designed.”

“I wanted to make it a social garden, not just a social house,” she says, “for the garden to be a space where people can create together. It’s a private garden but we are creating something that is communal. We are trying to make something communal within structures that are not communal, in the official sense.”

The Seed is also proud of its diversity: all its adult residents are immigrants, two are people of colour, two are queer women. “This is important for us,” Karoline says. “Here, four usually minoritised groups are in the majority, and we have found that this changes things. We interact differently, talk about different things, understand different things. The Seed is like a respite from the dominant culture.”

• The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations
• Andrew McCullough of Thermal Image UK using a smoke pencil to look for leakage during the blower door test Andrew McCullough of Thermal Image UK using a smoke pencil to look for leakage during the blower door test
• Heating is provided by a Daikin Altherma 3 air-to-water heat pump Heating is provided by a Daikin Altherma 3 air-to-water heat pump
• The garden is filled with mature trees and covered by a tree preservation order The garden is filled with mature trees and covered by a tree preservation order
• The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations
• The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations
• The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations The foundation consists of a suspended timber floor constructed on galvanized steel screw pile foundations
• Installation of the suspended timber floor, which is insulated with cellulose and sits on a truss lattice of timber beams that is ventilated underneath Installation of the suspended timber floor, which is insulated with cellulose and sits on a truss lattice of timber beams that is ventilated underneath
• Smartply Airtight OSB with airtightness taping at seams Smartply Airtight OSB with airtightness taping at seams
• Brick from taken down house used for gabions Brick from taken down house used for gabions
• Pro Clima Extoseal Encors weatherproof and watertight sealing tape around windows Pro Clima Extoseal Encors weatherproof and watertight sealing tape around windows
• Blower door airtightness test underway Blower door airtightness test underway
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In my time writing for Passive House Plus, we have covered many projects with deeply impressive fabric performance, energy demand and airtightness. But as with most of the building sector, we have always evaluated these buildings based on the amount of energy they consume per square metre of floor area. Meaning that someone can build a very large house, consuming far more resources than necessary, and still meet standards such as passive house, or the RIBA Climate Challenge (Ed.: the RIAI, to their credit, have set a more stringent embodied carbon target for homes of more than 133 m2 or smaller low density rural homes). A growing number of voices now argue that we need a robust way to measure energy use and embodied carbon per person too, as well as per square metre.

The Seed does challenge perceived wisdom about how much we need to live with. Does every home need a separate guest bedroom, for example? Its own laundry, tools, and other facilities? What else might we share if we lived closer together, while building community at the same time?

This writer lives with his wife in in a small cohousing project within a wider intentional community, Cloughjordan Ecovillage. Moving here has been one of the most rewarding decisions of my life, and it is now hard to imagine living any other way. It has opened my eyes to the extent to which community has been eroded from our societies, its critical role in climate and environmental action largely forgotten. Which is why projects like The Seed are so inspiring and illuminating.

This article was originally published in issue 47 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €15, or click here to receive the next issue free of charge

Cohousing aside, The Seed is also deeply impressive in terms of thermal and environmental performance. It was certified as a passive house just before this magazine went to print — all the more remarkable given that its H shape means it has a large surface area from which heat can escape, and given its foundation type – more on which later.

It was built with a prefabricated timber frame system from Eden Insulation in Cumbria, and insulated with cellulose and wood fibre, with airtightness provide by Smartply Airtight OSB. And it boasts a superb airtightness result of 0.19 air changes per hour.

But it is in the detailed thought given to embodied carbon and materials where The Seed really excels. Karoline developed the project with her ex-partner, and his desire to avoid the use of cement and concrete led to some innovative design decisions. Early on, KMA and the project engineer, Narro, produced a report looking at potential alternatives to concrete foundations.

KMA also evaluated the embodied carbon of the different options. A limecrete foundation was considered, but Karoline was keen to have large windows, and there was more chance of these shifting over time on limecrete.

Then Narro came across No More Digging, a Dundee-based supplier of screw piles and ground screws – large steel screws that are secured into the ground to provide a stable foundation. Steel industry progress on commercialising net zero carbon steel notwithstanding, steel is typically a highly carbon intensive material, and far higher than even concrete, pound for pound. Analysis by embodied carbon expert John Butler indicated circa 180 tonnes worth of concrete would be required to build a strip foundation for a development of this nature, including the foundation for the decking. This compares to circa five tonnes of screw piles, and roughly one-third of a tonne of concrete grout. Maguire had hoped to eschew concrete altogether, but a high-water table mitigated against this, meaning the use of concrete grout – which main contractor Billy Ferguson reckons added up to less than a cubic meter of concrete – to protect the steel.

At The Seed, the suspended timber floor is insulated with cellulose and sits on a truss lattice of timber beams that is ventilated underneath. This lattice in turn sits on the screw piles, which are anchored into the earth – which also means the site could be easily restored to a green field site, once this building reaches its eventual end of life, hopefully several hundred years from now. Brick salvaged from the old house forms the upper layer of earth here, while salvaged brick was also used to form the gabions for the retaining wall (in order to create a ventilated, suspended timber floor without raising the level of the house too much, it was necessary to dig down).

“There is a lot of really beautiful work underneath the building,” Kirsty says, praising Billy Ferguson and Paul Gordon of contractor Alpha Contracts for this.

Karoline says that building something innovative came with riskes as well as rewards: “It was a huge responsibility because I always wanted to make the perfect decision,” she says. “But I learned there is no such thing as the perfect decision. Because even if you find the right material, is it available in the UK? Are the skills available to install it?”

With a portfolio of ambitious ecological and low environmental impact projects under their belt, KMA are no stranger to exploring new architectural ideas, and Kirsty says that even though the project was innovative, her team approached it methodically. “We managed risk very carefully and gave Karoline deliverable options which were extremely well researched and low risk at each stage.”

She continues: “Karoline’s vision was this cohousing type living arrangement, and part of this project was exploring what that meant for her, to deliver the bigger picture she envisioned for the site.”

“There was a really interesting discussion about what cohousing meant, what would work. It was really just exploring a way for two families to live together. Karoline brought different voices into the design process along the way, and the fact the space would work for a range of different people, rather than just one set of people, is really interesting.”

Ultimately, The Seed hits impressive environmental benchmarks — passive house certified, low embodied carbon, an obsession with reusing materials — but it is as much about creating a space for community and nature as the building itself.

Kirsty says: “To Karoline, it’s a woodland garden that happens to have a house in it.”