Cairn is an architectural studio based between Edinburgh and London that specializes in creating low-carbon buildings. In its latest project — the renovation and extension of a Victorian terrace in Hackney, east London — Cairn has pioneered the use of a new low-carbon blended cement. “House made by many hands” is the first building in the UK to use Limestone Calcined Clay Cement: LC3.
LC3 is based on a blend of limestone and calcined clay, two materials with a synergetic effect. It was developed at the École Polytechnique Fédérale de Lausanne in Switzerland along with regional experts at the University “Marta Abreu” of Las Villas in Cuba and the Indian Institute of Technology Delhi. Traditional Portland cement consists of 95 percent clinker — production of this material is energy intensive and responsible for a large amount of CO2 emissions. LC3 is a blend of limestone (15%) and calcined clay (30%) with gypsum (5%) and clinker (50%) — the reduced clinker content cuts carbon emissions by up to 40 percent. LC3 can be produced using existing equipment and is mixed and poured in the same way as standard concrete.
Cairn describes the compact Victorian house renovation as a “test bed for LC3.” The studio says: “The project demonstrates how a Victorian house can be renovated and extended with a substantially reduced environmental impact — 40 percent lower than a typical build deploying conventional concrete, a steel frame box, and plasterboard.” LC3 has the potential to make a significant impact in the reduction of global carbon emissions — “1 to 2 percent if adopted universally by the construction industry,” says Cairn.
The home’s renovation and extension was commissioned by an environmentally-conscious client (a chef with a background in sustainable agriculture). The 77-square-meter (829-square-feet), two-story Victorian terrace sits on a densely populated, car-free street. The home occupies a narrow plot with no rear garden and a small strip of external space. Cairn’s challenge was to adopt a sustainable design approach through the reuse and repurposing of existing materials, creating a contemporary, bright, and airy kitchen. The studio identified, retained, and repurposed usable original elements, interweaving both old and new materials. Any new materials are bio-based, including the use of hempcrete (walls), cork, wood fibre, wood wool, and lime plaster.
Cairn worked with Structure Workshop, a London-based engineering design consultancy, to combine a floor slab made from LC3 with a hardwood frame that spans between the brick piers of the Victorian house; LC3 was also used to underpin the existing brick footings, helping to gain head height in the extension. “Unlike a conventional domestic extension, steel has been used sparingly,” says Cairn. “It forms footings and flitch plates at key connections and allows for demountable bolted connections.” The new floor has been lowered, helping to delineate the space.
The client and her partner were actively involved in the project’s construction, working alongside the architect and contractor to cast the hempcrete walls by hand (hence the “house made by many hands”). The walls have a timber frame and exposed hempcrete infill. A bio-based material, hempcrete is a composite of hemp shiv (the woody core of the hemp stalk) and a lime binder.
“Patent-glazing” on the extension roof significantly increases the amount of natural light; a new roof light in the ground-floor bathroom and openings in both new and old walls also improve daylight levels in what was a dark, cramped space. The renovation of an upstairs home office now includes access to a roof terrace. Lining layers are omitted wherever possible, ensuring the new hardwood timber frame is a key visual element of the ground-floor space. Any boards that were installed are made with a breathable wood wool and finished with lime plaster. A timber floor is made using wood reclaimed from Bow Street Magistrates’ Court as well as second-hand furniture and light fittings, imbuing the house with a certain vintage charm.
