When building an extension, be mindful of the overall carbon footprint of your home.
Image: Unique Home Stays
Planning and building an extension is a lengthy process and it's important to consider what effect it will have on the environment as well as the overall carboon footprint of your home. The Grand Designs magazine team spoke to Adam Knibb of Adam Knibb Architects on the best ways to aim for a low impact build that is carbon aware.
Zero carbon refers to both embodied energy, which is used in the manufacture of the building materials, and operational energy, which is used to heat, cool and power an extension. If the entire building isn’t being upgraded, then even if you deliver a zero-carbon extension the overall house will still have the same carbon footprint. In theory, the extension could be below zero, generating energy sufficient to power the house, but I haven’t heard of anything like this being done before.
Image: Mulroy Architects
Concrete is still the industry standard for foundations but it has high embodied energy. You can reduce the embodied CO2 of foundations through different cement mixes or use of limecrete, but not offset it completely. One of our new timber-frame houses is set on a compacted gravel trench foundation, using aggregate from the previous demolished house with mechanically compacted layers, topped with limecrete to bind it all together.
Read more: The Green Homes Grant hub
Build using timber frame, which has low embodied energy; all buildings ideally need to be constructed this way to minimise the environmental damage. Modern solutions such as SIPs (structural insulated panels) and CLT (cross-laminated timber) are best for reducing the carbon footprint.
Cob or straw bale could be used but it’s important to think holistically about the building. They don’t lend themselves to airtightness so additional membranes to reduce leakage will be needed.
Image: Simon Whitehead Architects
Follow the energy hierarchy: Be Lean – select the highest standards for materials. Be Clean – keep emissions low. Be Green – include renewables. Design your extension with good insulation, airtightness and building orientation in mind, then go for renewables such as air source heat pumps. The house will become more sustainable, with a lower carbon footprint, over time.