Sustainability Report

Embodied carbon overview

• During construction, the upfront embodied carbon was calculated at 436 kgCO2eq/m². This exceeds the targets set out in the LETI Guide and forms part of 31/44 Architects’ progression towards the 2030 target of 300 kgCO2eq/m².
• The house is constructed with a brickwork outer leaf and concrete beams. At ground floor level, a masonry inner leaf, painted brick, spruce panelling, and a small internal concrete frame define the structure. A limited number of concrete beams permit wide openings to the gardens.
• Upper floors and roof voids are timber framed to reduce the use of masonry. Timber spans were designed to avoid the inclusion of structural steel.
• Elements that appear to be concrete at eaves and roof edges are formed from lightweight timber construction clad in six-millimetre cement board. Tight joints create the appearance of solid components while reducing reliance on carbon-intensive concrete.
• Building in London typically requires piled foundations; in this case, the inefficiency of conventional concrete piling, often oversized due to design codes and lack of live structural feedback, led to the selection of steel screw piles. Screw piles provide precise feedback on ground resistance during installation, allowing only the required size to be installed. Their position was determined on site following hand-dug trial trenches to avoid damage to protected tree roots.
• The ground floor concrete slab is set at two levels. The upper level glides across the ground supported on carefully positioned screw piles. Deep upstands act as beams, reducing the piling required, forming a plinth to the building, and removing the need to excavate in these areas.
• Self-finished materials are prioritised and plaster finishes minimised to avoid high-embodied carbon wall treatments. At ground floor level this approach is contrasted with more conventional plaster finishes used within the heavily insulated timber frame of the first floor and roof voids.

Operational emissions overview

• The house is fully electric and does not have a gas connection. An air-source heat pump provides all heating and hot water.
• The house is largely triple-glazed and supported by underfloor heating, mainly within tiled floors. A large south-facing opening incorporates an integrated deep louvre, sized and angled to exclude high summer sun while admitting low winter sun.
• Ventilation follows traditional principles. A roof light within a double-height first-floor space facilitates passive stack ventilation, assisting summer cooling.
• The house has an EPC score of 81, with a predicted regulated energy use of 83 kWh/m²/yr. In operation, following a full annual cycle, the house runs at 47 kWh/m²/yr (unregulated). Measured total energy consumption has been under 60 percent of the predicted overall energy use over a twelve-month period.
• In operation, the house produces 1.78 tonnes of CO2 per year compared to 6 tonnes per year for a standard home. It uses 80 percent of the primary energy consumption initially predicted under the Standard Assessment Procedure.