Exposed concrete tends to be used for its cool, industrial aesthetic. But can it also be warm, natural – even homely? This is what architects Deborah Saunt and David Hills, partners at DSDHA, wanted to show when building their own family home in Clapham, south London. “Concrete is a beautiful material in the eyes of architects, yet often considered harsh by the public,” says Saunt. “We were keen to see if we could literally live with concrete and still enjoy it.”
(Mirrored window reveals blur the boundary between house and garden)
The Covert House has been built in a partitioned back-garden plot. Planning conditions dictated that the structure could be no more than one storey high, forcing Saunt and Hills to dig downwards – hence “covert”. The subterranean lower floor necessitated an impermeable concrete structure, but the architects decided to take this as a starting point to fully explore the material’s domestic side. The walls and soffits are all left unfinished, part of a simple palette that includes white resin floors, white metalwork and joinery, and a showpiece insitu white-concrete spiral staircase.
That this creates a sense of warmth rather than austerity is a testament to the quality of the in-situ concrete work carried out by White Rock Engineering. This had to be extremely precise while often appearing the opposite. Bespoke formwork was used for each detail, and the contractor was working to extremely high tolerances, creating 100mm-thick walls in places with minimum deviation. But shuttering joints are deliberately unaligned with architectural features, the elegant ribbed ceiling to the main floor does not match the wall panels, and blowholes under 10mm were left unfilled. “Where the lateral layers between pours are visible, there is a languid, almost landscape sense,” adds Saunt. “Children even say the patterning on the soffits is like cloudscapes.”
(The spiral staircase was cast in situ)
Even so, such an imposing concrete structure could still appear forbidding, particularly as the main living space and bedrooms are on the belowground level – accessed via the spiral staircase – and the self-compacting mix included 30% pulverised fly ash, giving a darker, slightly smoky quality. However, some clever interventions give the interiors a sense of lightness and accentuate concrete’s natural properties. Mirrored window reveals blur the boundary between garden and interiors, creating kaleidoscopic refractions of the greenery. And lightwells, concealed from outside view, draw daylight deep into the building, giving a lustrous quality to the patinated walls.
(Lightwells and full-length glazing illuminate the lower level)
The effect is more that of a garden pavilion than a basement. The use of concrete helps to create a good home in another sense too. The thermal mass of the structure and the surrounding earth prevents summer overheating and reduces energy demand in winter. Add in the underfloor heating (which is even built into the in-situ staircase), and the Covert House really is warm in every sense.
Structural engineer: Price & Myers
Contractor: Whiterock Engineering
Source: Concrete Quarterly, Spring 2015