The home of architects Deborah Saunt and David Hills of DSDHA, Covert House in south London is a case study on the potential of unlocking urban backland sites. Just a single storey is visible above ground, with a subterranean level that still manages to be light and bright and connect with nature, through the use of courtyards and reflective materials. Its use of concrete is also unusual, lending character and warmth rather than the cold industrial feel with which the material is usually associated. Here, Deborah explains how this project took shape.
Why ‘Covert House’ – is it particularly hidden from view?
It is indeed. Even though it is just two miles from Parliament Square and the West End, Covert House is entirely shielded from street view. It’s set behind a terrace-lined residential block in Clapham Old Town, in a backland site within a Conservation Area that can only be accessed via a narrow passageway that cuts through one of the houses on the main road.
Were you working under severe constraints on such a tight urban site?
Working in a Conservation Area in London brings huge constraints. To meet local planning policies, we were limited to a single-storey height, which is why we decided to partially lower the structure within the garden plot.
The house follows some very strict rules in terms of not encroaching on the quality of existing gardens. It has a stepped roof line, so it is lower close to garden boundaries, and it never goes above the height limits established in conversation with the planning department (2.5 to 3.5m, broadly the same height as existing domestic sheds and summerhouses in the local gardens).
Simply gaining access to the site was one of the main challenges. As we had to excavate five metres into the ground, we needed large digging equipment. We had to outsource a particular brand of machines produced in Japan – the only ones narrow enough to make it through our passageway (after their door handles were removed…).
How are the living spaces split above and below ground?
The open-plan ground floor contains the kitchen as well as the dining and living room areas. These spaces are flooded with light and connected to the outside through skylights above and full-height glazing that carves out a series of views on to the garden.
Accessed via a white concrete stair, the lower level is embedded in the earth and hardly visible from the exterior, yet visually connected to the garden from every room via two courtyards. This floor is divided into smaller private bedroom and bathroom spaces, which can all be accessed off an informal living room area, without corridors or wasted circulation space.
How do you live here?
It is brilliantly flexible: you can either come together in the large open-plan ground floor, or have two acoustically separate spaces by using the other living room downstairs, where the children want to make noise or use technology or watch a film. There is also a discreet study area away from the action, within the master bedroom suite.
Can you explain more about the use of concrete in this house?
Given the contradiction that concrete is a beautiful material in the eyes of architects, yet often considered harsh and rather inhuman by the lay public, we were keen to see if we could literally live with concrete and still enjoy it, and maybe set a new example. So far, everyone who visits seems to be impressed at how domestic the house feels despite its rigour.
As the dimensions of the site were rather modest, we aimed at increasing the living space by keeping the structure to a minimum, so we employed a system of king piles, with the timber formwork set between them. Given our height restrictions, our aim was to minimise the roof slab as much as possible, so we decided to complement it with ribbed beams which incorporated ‘drapped’ and standard fixed reinforcing.
It is generally much easier to cast the concrete with a tower crane and in large volumes, but in this particular case our concrete contractor, Anthony Thresh, was required to produce extremely slender slabs, columns (75mm wide) and walls (100mm thick) which obliged us to only pour a relatively low volume of concrete each time. Each operation had to be carefully coordinated to prevent the concrete from hardening before it could be poured, especially in hot weather.
What purpose do reflective elements such as mirrors and the pool serve?
The chamfered mirror reveals to the full-height windows dissolve the bulk of the walls and camouflage the house within its verdant surrounding. The mirrors also reflect sunlight over the day, creating an ever-shifting sequence of reflections both internally and externally.
The southern courtyard grants each bedroom access to the outdoor space; it’s stepped, bringing more light to the lower level and also creating a series of protective layers that accommodate an in-built planter and a linear pool. Together with the mirrored panels, it generates a game of reflections, helping to neutralise the sense of enclosure one might feel while being partially underground.
Are there any other innovative design features?
By using a whole-house ventilation system we recycle heat that builds up in the kitchen and bathrooms and recycle that back into the heating system for both underfloor heating and for hot water. We also have solar thermal panels on the roof to improve hot water production, and an air-source heat pump.
What was your approach to furnishing the space?
Only a few transitional elements – the thresholds between interior and exterior and the staircase for instance – are made of white concrete (a mixture of marble sand, white cement and a colour enhancer); the rest of the structure has been left raw, so the concrete’s texture became an important element of the project. We didn’t want the imperfections to be completely erased, which gives a kind of liquid quality to the wall finishes and the ceilings, and paradoxically a homely feeling to the place. We completed the material palette with marble and white resin floors.
With the interior, the effort has not been so much that of ‘softening’ the feel of the concrete, but rather to ‘visually edit’ its elements – mid-century modern furniture and pieces we have designed, bespoke concealed lighting or artworks – to avoid anything that might clutter the space and overshadow the home’s relationship with nature and the light within it.
Do you have a favourite spot in the house?
The living room on the ground floor is phenomenally tranquil and makes you feel as if you are in another world entirely, not close to central London.
Has anything surprised you about the house now that you live there?
The lower level exceeds our expectation, with so much light – in fact most people remark that it is hard to believe you are below ground.
Has this project informed your subsequent work?
We feel that the building is a prototype for healthy living. Not just because of the sense of wellbeing that is generated from the building having fresh comfortable air and the comfort of a good ambient temperature, but the psychological benefits of having visual access to trees and greenery at all times, especially when housing is at lower basement levels. Designing with green views has been the subject of research in healthcare where it has been demonstrated to improve lives and save money for healthcare clients; we are interested at the same phenomenon in domestic and working environments.