Set on a contaminated and constrained brownfield site behind a row of terraced houses in East Dulwich, Niwa House was never going to be straightforward. The brief called for an accessible family home with a generous internal feel, while keeping a low profile to respect strict height constraints. Designed with Takero Shimazaki Architects, the house draws from Japanese influences and makes a calm retreat out of a tight and complex site.

The client’s desire for a highly glazed façade posed a challenge. Glass brings light, but it also risks overheating. Instead of seeing this as a problem to remove, we treated it as a spur for innovation in the engineering. Working closely with our in-house MEP team, we developed a structure that would also regulate the environment, giving the building enough thermal mass to avoid mechanical cooling altogether.

The result, a composite stone and timber superstructure, the first of its kind at this scale.

Thin stone slabs work in compression, glulam beams in tension, and together they form a system around 150% stiffer than timber alone. The stone provides the thermal mass that keeps the interiors comfortable, without mechanical ventilation, while the slimmer timber sections create a refined exposed frame. It is structure, architecture, and environmental system rolled into one.

Structurally composite behaviour © Webb Yates

This hybrid approach was not an experiment built from scratch. It drew on more than eight years of research with The Stonemasonry Company and UCL, testing and refining the use of stone, including for composite action. We had proven the mechanisms involved on smaller projects and in the lab. Niwa House, with its ambitious client and design team, was the ideal setting to take it further.

Innovation at this scale comes with risk, so safety and reliability were at the centre of the design process. We developed detailed models to understand the behaviour of the system under different loading conditions, including long-term timber creep and local stresses in the stone. The structure relies on composite action for serviceability but is designed so that if the composite behaviour were ever lost, the timber beams alone could carry the loads. That layered safety gives robustness without over-design.

The real beauty lies in the simplicity of the detail. Composite action comes from geometry, not mechanical fixings. Stone slabs are not bolted down but held by end restraints, which makes the system easy to assemble and, in the future, easy to take apart. At end of life, the stone can be lifted out and reused, and the timber frame unbolted and reassembled elsewhere.

The team also worked hard to keep the fabrication as low impact as possible. The timber was prefabricated from a fully coordinated 3D model, reducing waste and simplifying site work. The stone was sawn flat at the quarry with limited processing, avoiding the high carbon footprint of carving and finishing.

Niwa House shows what can happen when architecture and engineering move forward together. The client’s ambitions, the architect’s vision, and the structural response aligned to produce something both discreet and ground-breaking. Stone and timber each play the role they excel at and, in doing so, they create a home that proves innovation is not about complexity, but about making the most of simple, honest materials.

It’s a delight to see this seemingly humble project among giants on the Stirling Prize shortlist, though those who know the quiet ingenuity behind it will understand why it is there.