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Ben Allen’s House Recast in north London rethinks the home extension with pigmented precast concrete 

Colourful, concrete, a bit gothic … not words you would normally associate with a north London back-of-house extension. After all, these projects tend to be exercises in drawing light into narrow, deep-plan Victorian terraces, and if there is an aesthetic, it is usually a sort of glazed-box minimalism. But when Studio Ben Allen was invited to add a new kitchen and two bathrooms to the back of a house in Hackney, north London, it took a more vibrant approach – exploring the possibilities of pigmented precast concrete.

The project may be tucked away at the rear of the property, but it has already turned heads – not least at New London Architecture, which gave it first prize in its recent home improvement awards. It is a dramatic sequence of spaces: the double-height kitchen, with its coral-pink precast countertop and workbench; the curved void to the balustraded gallery; the hammam-like bathroom, which feels almost hewn out of deep-green concrete; all culminating in the rear elevation of scallop-patterned green columns and beams and pink wall panels.

The extension naturally reflects the tastes of the owners, but the material palette was also about offering a comforting robustness, says practice director Ben Allen. “There’s a nice sense of enclosure when you’re inside a building that’s very solid.” Even so, precast concrete is not an obvious structural material on such a small project. Allen and his colleagues were partly driven by an interest in investigating why that is. “Part of being a smaller practice is that we can ask if there are ways of doing things differently. Modular construction often looks industrial, but we wanted to push the aesthetics and do something that surprises people.” 

The idea developed into an exploration of concrete as structure and finish combined, with pattern and pigmentation integrated into precast units. Working with Cornish Concrete, the aesthetic quickly took shape: “There wasn’t a lot of trialling. We knew what we wanted in terms of colour, and we had to be quite decisive. The client knew it was going to be playful, engaging, and for us it was a bit of an experiment, so we were willing to take a few risks.”

Cornish cast the main structural elements – columns, beams and external wall panels – using a standard mix, with added pigment. The colours, Allen says, take their cues from the red brick of the 19th-century neighbourhood and the buildings of project architect Omar Ghazal’s Jordanian heritage. “We were interested in the strong palette of late Victorian gothic – with its deep reds and mint greens – and the client wanted something quite exotic, so we had this idea of a hammam-like bathroom.” Another decorative flourish is the scallop pattern, which picks up on the detailing of the bathroom’s lattice screen and changes subtly as it rises up the facade. This was cast using a flexible mould from a bespoke design by the architects.

Internally, the colours continue to unfold, with stairs, counters, sinks, benches, bath and washbasin all precast in fibre-reinforced concrete by Kent-based specialist Concreations. Diffuse light from semi-circular vaults above the bathroom and kitchen lends warmth to these stone-like forms. The discrete spaces are connected in compelling ways – a void, a raised arch, a bright-red stair – and the eye is continually drawn to these cast elements.

To some extent, this was an experimental project, testing the water for precast concrete used structurally, visually and on small projects. One challenge Allen says they would address differently next time is site assembly. The initial plan was to crane the elements over the house, but the required road closures proved prohibitive. Instead, they had to be taken through the house, which meant dividing the bathroom wall into three sections. Even so, erecting and sealing the structure still only took five days.

It is a persuasive reason to continue exploring the use of precast concrete in domestic renovation, and Allen is up for the challenge. “We’ve gained so much knowledge in terms of how to do this – from the size of the panels to connection details. The more you push the limits, the more you learn from it.”

Project Team


Studio Ben Allen

Structural engineer


Main contractor​


Concrete Contractor

Cornish Concrete

Date of completion



Keith Hunter Photography / Reiach and Hall Architect