London-based architectural firm THISS Studio has completed a groundbreaking residential extension project that challenges conventional approaches to small-scale domestic architecture. The Butterfield House Extension, located in Stoke Newington, demonstrates how innovative material choices can support sustainable construction practices while creating compelling living spaces for modern families.
The project transforms a standard post-war terraced house through the experimental use of Porotherm, a precision-engineered clay block walling system typically reserved for large-scale commercial developments. THISS Studio reimagined the potential of this industrial material by bringing it into a residential context, creating a 113-square-meter extension that opens the home to its garden while providing more generous, connected living spaces for a family of four.
Encouraged by their clients' strong commitment to environmental responsibility, THISS Studio approached the brief with a focus on material sustainability and innovation. The extension utilizes distinctive, singular extruded clay blocks that enable solid wall construction, designed to perform all necessary wall functions by integrating structure, insulation, and finish in a single system. This approach eliminates the need for conventional linings or additional insulation while significantly reducing the use of concrete and cement.
The Porotherm system features an interlocking design that simplifies installation and eliminates vertical mortar joints, further reducing material consumption. Internally, the exposed blockwork creates a striking, minimalist finish where blocks are stacked atop one another, forming an honest, materially rich surface that complements the home's unique 1970s brickwork. Externally, THISS Studio experimented with bespoke cut tiles created from the Porotherm blocks, reimagining the block's distinctive multicellular structure as a subtle decorative element on the rear elevation.
The project exemplifies THISS Studio's resourceful and low-impact design philosophy through its palette of affordable, readily available materials. Custom-built joists and engineered timber trusses were fabricated on-site from pine battens to support the extension roof, while pine furniture board and repurposed components were incorporated throughout. Generous expanses of glazing help natural light penetrate into the home's deep and narrow layout, counteracting any potential darkening from the addition while creating a sense of openness within the modest footprint.
Built on a World War II bomb site adjacent to Stoke Newington's Butterfield Green, the project faced significant foundation challenges. Layers of old rubble required extensive excavation to a depth of six meters before reaching stable clay. The architects responded by adopting a lightweight screw-pile system and floating concrete slab, avoiding the high material demands of traditional ground-bearing slabs. This bespoke foundation solution not only addressed the complex site conditions but also reinforced the project's commitment to limiting material use at every construction stage.
The extension was completed in 2025 with structural engineering by Blue Engineering and construction by YG Builders LTD. Materials used include products from Art Steel, Dulux paint systems, Husk, and the featured Porotherm clay blocks. Photography by Henry Woide captures the project's innovative material applications and spatial qualities.
Despite its modest scale, the Butterfield House Extension offers a thoughtful examination of how material choices can support environmentally conscious construction in everyday residential architecture. As both structure and surface, Porotherm became a testing ground for integrated design thinking, quietly demonstrating the versatility and environmental potential of clay materials in domestic settings. The project stands as a compelling case study in material innovation and sustainable practice, showing how architects can transform standard extension briefs into opportunities for architectural experimentation.
