Sustainability Report
Embodied carbon
Embodied carbon overview
- Hempcrete blocks and hemp insulation batts, supplied by The Hemp Block Company, were used to create a carbon-negative, breathable, and highly insulated wall system. They help improve indoor comfort, reduce operational energy use, and support low-carbon design goals. The blocks were also easy to cut and enjoyable for the site team to work with.
- The interior of the extension was finished with hemp-lime plaster — Breathaplasta UNIVERSAL by Adaptavate — chosen for its tactile finish and healthy, breathable qualities.
- The SCORS Rating of A was fundamental to the structural design of the extension. The homeowner is a structural engineer; having spent much of their professional life reducing embodied carbon in clients’ buildings, they wanted to apply the same approach to their own home.
- Lightweight construction was key, avoiding heavy brick finishes in favour of a simple, exposed timber frame. As the house backs onto a park and is surrounded by trees, traditional concrete trenches would have required deep footings. Working with structural engineer George Reed of Price & Myers, Whittaker Parsons used carbon modelling tools to refine the structural approach, supporting the extension on screw piles and halving the embodied carbon in the groundworks, saving over two tonnes of carbon.
- The estimated embodied carbon for the new-build elements, comprising the rear extension and new porch, is 250 kgCO2e/m². This is substantially lower than the RIBA 2030 Climate Challenge embodied carbon target of 625 kgCO2e/m² for residential new-build projects, representing a reduction of approximately 60 percent against that benchmark. Subject to the assessment methodology and scope being directly comparable with the RIBA target, this demonstrates a strong commitment to sustainability and responsible resource use.
Operational Emissions / Energy
Operational emissions overview
- The home’s EPC rating improved from 63 (D) to 96 (A) following an extensive retrofit, including a high-performance extension, triple glazing, loft insulation, solar PV panels, an air-source heat pump, and heating system upgrades.
- Estimated annual carbon emissions fell from 3.9 tonnes of CO2 to minus 0.3 tonnes of CO2. The property’s solar PV system and air-source heat pump contribute to a fully electric strategy in which the home is estimated to offset more emissions than it produces.
- An air-source heat pump supplies hot water and heating, while rooftop solar panels provide up to 50 percent of the household electricity.
Afterlife
Phased construction and long-term flexibility
Considerations around reuse, phased construction, future flexibility, non-toxic materials, and the long-term use of materials played a central role in the design process from the beginning. The project’s approach to construction, material use, and long-term flexibility was shaped by a practical challenge: the clients needed to remain living on site throughout the works.
Initially, the family had planned to build a separate outbuilding to live in during construction. Following discussion, Whittaker Parsons proposed a phased construction strategy instead. The extension was built first, while the family continued to live in the main house. Once complete, they moved into the extension, allowing the renovation of the existing house to take place with minimal disruption. This phased approach reduced the need for temporary accommodation.
Future flexibility was also important. The home was designed with a long-life, loose-fit approach so it can adapt as family needs evolve. The extension serves as both additional living space and a self-contained apartment, with rooms that can shift between uses, from study or playroom to guest accommodation, utility space, or housing for extended family. Its adaptability was tested in real time when the family lived exclusively in the extension for four months while the main house was being renovated.
Together with accessible features and flexible open-plan spaces, the project is designed to support changing lifestyles. Material efficiency and long-term stewardship were embedded throughout the project through minimal site clearance, waste-conscious dimensional coordination, modular tiling layouts, and FSC-certified timber.
Key products in low carbon design
