Big open-plan living, dining and kitchen space looking out to the garden

How to reduce the carbon footprint of an extension

The steps you can take to limit the environmental impact of your new addition

By Becca Green |

When planning to build an extension to your home, consider how to reduce the carbon footprint of the project. Architect Adam Knibb of Adam Knibb Architects explains the measure you can take.

Embodied and operational

Two elements make up an extension build’s carbon footprint. Its embodied energy arises during the manufacture of any materials making up its construction, when CO2 releases into the atmosphere. The operational energy refers to the heating, cooling and power requirements of the extension. Even if you deliver a zero-carbon extension, if the entire building is not having an upgrade, 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. However, it isn’t a common practice for reducing the carbon footprint of your extension.

Rear exterior of Victorian house with side and rear extension

Side and rear extension to a Victorian terraced house. Photo: Rachel Whiting

When planning to build an extension to your home, consider how to reduce the carbon footprint of the project. Architect Adam Knibb of Adam Knibb Architects explains the measure you can take.

Embodied and operational

Two elements make up an extension build’s carbon footprint. Its embodied energy arises during the manufacture of any materials making up its construction, when CO2 releases into the atmosphere. The operational energy refers to the heating, cooling and power requirements of the extension. Even if you deliver a zero-carbon extension, if the entire building is not having an upgrade, 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. However, it isn’t a common practice for reducing the carbon footprint of your extension.

Rear exterior of Victorian house with side and rear extension

Side and rear extension to a Victorian terraced house. Photo: Rachel Whiting

From the foundations

Concrete is still the industry standard for foundations, but it has high embodied energy. You can reduce the embodied CO2 of your foundations through different cement mixes or use of limecrete, though this won’t offset it completely. One of the new timber-frame houses is set on a gravel trench foundation using aggregate from the demolished house. The mechanically compacted layers are topped with limecrete to bind everything together.

Using timber frame

Build your extension using timber frame, which has low embodied energy. All building construction needs to use such materials and methods to minimise environmental damage. Modern solutions such as SIPs (structural insulated panels) and CLT (cross-laminated timber) are best to reduce the carbon footprint of your project.

Plus Rooms Kitchen Extension Fellbrigg Road SE22 resized

A timber-framed flat and pitched roof design by Plus Rooms

Traditional materials

Cob and straw bale are other building material options. But it’s important to think holistically about the structure. Neither lend themselves to airtightness so you’ll need additional membranes to reduce leakage.

Follow the eco mantra

Keep in mind the energy hierarchy to reduce the carbon impact of your build:

  • Lean – select the highest standards for materials
  • Clean – keep emissions low
  • 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.

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