Casting off

Origin story: Soboro, London

Chris Twaddle on a house that finds space for the rusticated and refined sides of concrete

Soboro came about when the owner of an end-of-terrace Victorian property saw the possibility of building a house in the garden, on the plot of a former garage. He called the local council to ask for advice and they recommended he contact our studio. We knew the council was generally supportive of buildings that didn’t just follow the standard narrative on these types of plots and hoped this was why we were put forward.

The idea of a concrete building emerged early on. The plot was between stucco / painted brick and late 20th-century brick and we were looking for a material that would work in this situation. The small footprint meant that a basement was always going to be part of the scheme, which also pointed towards concrete.

There was an urge to exploit the variety found within a single material. Rustication came into the equation as a way of differentiating the basement and ground from the upper floors – the difference here being the heaviest rustication would be seen internally rather than from the outside. When we first discussed the project, our structural engineer Tim McFarlane described it as “an essay in concrete” – Tim is an inspiration and development meetings with his soft pencil in hand were always great.

This way of thinking conjured up ideas of something hewn from the ground and formed with a pattern of solids and voids. A cuboid was cut into the front elevation to form a terrace and a box protrudes at the rear as part of the bedroom. Lightwells were positioned at the front and rear to allow natural light into the basement. We also realised that, with the use of concrete, the basement could extend under the garden of the main house, doubling the size. This further reinforced this idea of digging out and casting spaces in the ground.

I studied at Duncan of Jordanstone College of Art (Dundee School of Art) in the brutalist nautical Matthew Building, designed by James Paul. I can still recall questioning why we could see woodgrain markings on the concrete – we didn’t know how or why this occurred but liked it a lot. Twenty-five years later, I would show our client for this project a photograph of the effects of light on the Matthew Building’s board-marked concrete to illustrate the effect we were trying to achieve.

In Soboro, there is a certain depth and at the same time simplicity that would be hard to achieve in any other material. The timber shuttering was made into panels off site, carefully set out both in width and variation of depth and rubbed down to make the grain more pronounced. After sampling various concrete mixes we decided the batch delivered to site was going to work well although the precision of the factory-made samples isn’t there and natural variations occur. This was seen as a feature of the material, the variation adding interest, not unlike the qualities found in timber.

On the upper floors, precast panels allowed concrete to be exposed inside and out, with the insulation sandwiched in between. From the exterior, grit-blasted panels on the lower floor and acid etching on the upper level continue the rustication. Internally, a glass-smooth “as struck” finish made a distinct contrast to the textured underground space.

Excavating a basement in a tight urban site can be tricky, and this was no exception. Watching it progress gradually – due to the sequential nature of the in-situ elements – added to the sense of slight apprehension. It wasn’t until much later, when the slab and lid were on, that the qualities of the operation could be appreciated. Deliveries of panels and demi-decks for the upper floors took place in an incredible two days – watching the panel installers crane an 11-tonne panel into place was remarkable.

Chris Twaddle is co-founder of kennedytwaddle

Photos Henry Woide