Sustainability Report

Embodied carbon

The embodied carbon (LCA Modules A1 – A5) of the Arbor House is measured at 376.4 kg CO2 eq/m2. This figure accounts for the impact of carbon associated with construction materials, transport of these materials to the site, and the construction itself. 

The home’s high fabric spec increases embodied carbon as more materials were used. The high use of PIR insulation, containing polyurethane in the form of a rigid foam, contributes most to embodied carbon. The next biggest contributor is the use of metal: structural I-beams and rebar in the foundations are made with steel; the window frames are made with aluminium. However, the substantial use of sustainably sourced timber counteracts these materials and contributes to a reduction in the embodied carbon level.

In the UK, the suggested embodied carbon benchmark for newly built properties — constructed in the 2020s — is 500 kg CO2 eq/m2 (a figure determined by LETI, a network of built environment professionals). The Arbor House therefore achieves a lower embodied carbon level.

Whole Life Carbon

Whole Life Carbon (LCA Modules A1 – D4) is measured at 802.9 kg CO2 eq/m2. This calculation accounts for all the carbon associated with the Arbor House throughout its estimated 60-year lifespan: materials, transport, construction, recurring replacement of materials (wear and tear), energy use, water use, and end of life impacts.

Standard Assessment Procedure methodology was used to calculate the energy performance of the Arbor House (the UK government’s recommended system for measuring the energy rating of residential homes). The Arbor House is thoroughly insulated, resulting in low heating demands. The dwelling is heated via a ground source heat pump that provides renewable heating. A mechanical ventilation heat recovery (MVHR) system improves air circulation. These measures reduce the home’s operational energy costs and carbon emissions.

The Arbor House utilises low-carbon electricity and a wood burner has been installed. The home’s operational carbon performance, associated with regulated energy, is measured at 3.20 kg CO2/yr/m2.

U-Value

The U-value performance is calculated at 0.37 W/m2K. This figure is a combined average for walls, floors, roofs, windows, and doors, and is significantly lower than the baseline U-values set out in the Scottish government’s “Building Standards Technical Handbook 2020” for domestic properties. The thickness of PIR insulation in the external walls significantly reduces heat loss.