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Architects: Cairn
- Area: 70 m²
- Year: 2024
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Photographs:James Retief
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Manufacturers: Xylo
Text description provided by the architects. Working against the grain and thinking outside the conventional steel and stud wall box, emerging architecture practice Cairn has pioneered the use of a new low-carbon concrete in its latest project, a house renovation and extension in Hackney, east London. House-made by many hands is the first building structure in the UK to specify a low-carbon limestone calcined clay cement (LC3) concrete, a new material that generates 30-40% less CO2 in its production than standard Portland cement. Commissioned by an environmentally conscious client, the compact Victorian house renovation has been a testbed for LC3, a product that can reduce total global CO2 emissions by 1-2% if adopted universally by the construction industry. The project demonstrates how a Victorian house can be renovated and extended with a substantially reduced environmental impact – 40% lower than a typical build deploying conventional concrete, steel frame box, and plasterboard.
Located on a densely inhabited, car-free street, the two-story terraced 77m2 house occupies a constrained site with no back garden and only a thin strip of external space. As found, it was dark and cramped. The challenge was to work with what was there, designing as sustainably as possible through reuse and repurposing of existing materials to bring it up to modern-day standards, creating a homely and productive new kitchen for its owner, a chef with a background in sustainable agriculture. The highly bespoke project carves light and space into the house. Cairn, working with structural engineers Structure Workshop, has combined LC3 for the floor slab, with a hardwood frame spanning between the brick piers of the Victorian structure. Unlike a conventional domestic extension, steel has only been used sparingly, forming footings and flitch plates at key connections, and allowing demountable bolted connections.
An explicit strategy of reuse underpins the whole project. Adopting a fabric-first approach, identifying what was essential, retaining usable original elements, constructing cautiously, and interweaving old and new, have been fundamental to the project. Rather than overhaul the servicing of the house, interventions have been simple and low-tech, selectively using what was found (relocating the combination boiler rather than consigning it to a skip), supplemented with energy-saving strategies, such as double-glazed windows. Client and architect were committed to repurposing and, where new materials were necessary, bio-based materials - hempcrete, cork, woodfibre, woodwool, and lime plaster – were specified, to improve health and wellbeing benefits. Lining layers have been omitted where possible, revealing structure and frames so that the new hardwood timber frame forms a key visual component of the ground floor spaces. Where boards were installed, breathable woodwool was used finished with lime render, and the new kitchen worktops by Foresso are made of recycled waste wood products. The result is an airy home with warmth and earthy textures, where old and new blend, celebrating the patina of time.
The ground floor renovation places the new spacious kitchen at the heart of the house. The floor has been lowered to improve head height and the space benefits from improved connections to the living room clearer sightlines and access to outside spaces. Upstairs improvements have been made with a renovation of the home office, which now has access to a roof terrace. Daylight levels have been significantly increased on the ground floor with patent-glazing to the extension roof, a new roof light above the tiled ground floor bathroom, and openings puncturing old and new walls. There are no internal doors on the ground floor, apart from that to the bathroom, to prioritize the enjoyment of visual connections and borrowed light. Spaces retain their character without doors to shut them off and are instead defined through considered placement of structural piers and changes in floor level. House made by many hands is the first building structure in the UK to use limestone calcined clay cement (LC3). The technology was developed in Switzerland at EPFL, along with experts in Cuba and India, and has vast potential to reduce the concrete industry’s carbon emissions. Concrete made with LC3 looks like conventional concrete and it is mixed and poured in the same way, requiring no additional site training. It has been used here in the floor slab; it was also used to underpin the house’s existing brick footings to gain head height in the extension.
The project has been an exercise in balancing the constraints of regulations with repurposing existing infrastructure, with the design being driven by the low carbon content of the materials, their buildability and cost. Cairn worked closely with structural engineers Structure Workshop, using the practice’s copyrighted Carbon Calculator to make embodied carbon calculations, informing the choices and quantities of materials. The client and her partner have also actively participated in the project, working alongside the contractor and architect to cast by hand the hempcrete walls (timber framed with exposed hempcrete infill). The decision to make the walls by hand, replacing power tools with human energy, resulted in a rewarding collective activity and a project made by many hands: the hands of the architects, engineers, contractors and clients. This collective endeavor was echoed in the site hoardings which were printed with a montage of sketches on the theme of the House of the Future by pupils of the adjacent primary school: a hoarding made by many hands. The approach to the base-build of the home is complemented by the furnishing and fittings within. These are re-used and given a second life wherever possible, such as the timber floor which has been reclaimed from Bow Magistrates Court and a collection of second-hand furniture and light fittings. The client was determined not to use new items, unless unavoidable, so that the house is imbued with character and unique histories.
