Sustainability Report

The carbon breakdown was completed at the end of the project: RIBA 2030 Stage 7, assuming cradle to practical completion. The calculations were completed using the Mesh embodied carbon calculator. Embodied Carbon RICS Modules A1-A5, B1-B5, C1-C4 were considered. D was also recorded.

This extensive retrofit project achieves the RIBA Climate Challenge 2030 targets for operational energy use; in addition, the home is designed to minimize the amount of embodied carbon.

Collective Works identified the potential for improvement in all areas of the home. Adopting a circular approach to demolition and reuse, the studio retained as much of the original structure as possible and reused materials whenever feasible. For instance, existing timber studs were reused in new stud walls, while bricks from a demolished rear wall were repurposed to construct an internal wall.

Screw piles instead of a concrete raft reduced the impact on the foundations. A Steico timber construction system was used to build the extension. Natural materials like sheep wool for insulation and natural finishes were prioritised throughout the project, which helped reduce embodied carbon and any off-gas emissions.

Mid Terrace Dream employs Passivhaus performance standards of energy efficiency and thermal performance. The building’s existing envelope, roof, floors, and new extension are exceptionally well-insulated, reducing thermal bridges; all windows are triple glazed and can be opened to provide natural ventilation.

Airtight construction of the building achieves a U-value of 1.8m3/(h·m2) at 50Pa — this is well beyond the current building regulations for new buildings and demonstrates the home’s superior airtightness and insulation. The house is entirely electric, apart from the gas hob, which was a client request.

The property utilizes energy generated from rooftop photovoltaic panels with additional battery storage; this is supplemented by a green power supply.

An air source heat pump provides both space heating and hot water; Mechanical Ventilation with Heat Recovery provides the home with fresh air while recovering heat from the stale air that has been expelled. A green roof on the extension contributes to water management.

• Overall Area Weighted U-value: 0.23 W/m2K (Pre-retrofit: 20 W/m2K)
• Airtightness: 1.3m3/h/m2 at 50 Pa (Pre-retrofit: 10 m3/h/m2 at 50 Pa)
• Operational energy: 27 kW/m2/yr (Pre-retrofit: 270 kW/m2/yr)
• Annual energy bills: £69 rebate (Pre-retrofit: £2000)