Whole Life Carbon Assessment
Verco was commissioned by AIMCH housing developer partners Stewart Milne Group (SMG), Barratt Developments PLC and London and Quadrant Housing (L&Q) to undertake whole life carbon assessment across four homes. The aim was to evaluate the embodied carbon impact of concrete masonry built homes compared to open and closed-panel timber frame construction under current English building regulations (Approved Document L, published Mar 14).
In the future, additional modelling will be undertaken to assess the implications on compliance to Jun 22 AD- L building regulation changes and Future Homes Standards in England and Wales.
summary
The core findings from the whole life assessment are:
- As expected, that the operational energy emissions (the in-use stage) during the 60-year modelling period are the largest contributor to the whole life carbon footprint of the homes. This finding does not differ between construction types.
- In a typical four-bed detached home, timber frame wall elements save five tons of CO2e whole life carbon emissions compared to aerated concrete wall elements – that's equivalent to 16,500 road miles*.
- Timber frame wall elements sent to landfill produce up to 15% more carbon (0.5 tCO2e) at end of life compared to aerated concrete blocks.
- As operational emissions drop due to implementation of the Future Homes Standard, the lower whole life carbon benefits of timber frame will become increasingly beneficial compared to aerated blockwork.
- Strip foundations, external, party and loadbearing wall elements, roof tiles, ground floor slabs and underbuilding walls are the key elements that contribute to the embodied emissions of the homes. These elements do not vary between masonry and timber frame construction methods, except where there are design-specific point loads requiring extra concrete in the foundations.
Note: * 1tCO2e = 3,300 road miles in medium sized petrol car (DEFRA 2021)
SCOpe
The embodied carbon analysis is based on the RICS Standard for Whole Life Carbon Assessment.
Methodology
The model assesses the embodied carbon of the houses and their component materials on a cradle-to-grave basis, using the RICS Standard for Whole Life Carbon Assessment. Of note are:
Timber and Carbon Sequestration
For timber and timber-derived products, this approach allows for the inclusion of emissions arising from the decomposition and incineration of timber at the end of its life, making it possible to include the relative benefits of carbon sequestered within timber based products used in all construction methods. In accordance with the RICS whole life carbon assessment for the built environment professional statement (2017):
End of Life
End-of-life disposal methods (recycling, reuse, landfill, biomass etc.) represent current practices and might not reflect those in 60 years’ time.
Trends have not been projected for future rates of recycling and reuse for the purposes of this project.
There are several inconsistent conclusions from different sources for timber end of life treatment, ranging from <1% to 25% to landfill, as well as uncertainty around actual disposal practices at end of life in 60+ years’ time. (See Appendix B)
Assuming the same proportion to landfill for both timber and aerated concrete blocks, therefore, allows comparison purely on material characteristics.
The modelling assumes 10% to landfill and 90% recycled, for both aerated concrete blocks & timber elements, used within the differing construction methods.
Summary Report
A summary report has been produced to compare four typical UK house typologies, comparing concrete masonry construction and open/closed timber frame construction methods, to England and Wales Approved Document L building standards (published Mar 14).
The Full Detailed Whole Life Carbon Assessment Report is commercially restricted to AIMCH partners. However this may be released to third parties where appropriate to do so and with the consent of all partners.
Additional modelling will be undertaken in the future to assess the implications on compliance to Jun 22 AD- L building regulation changes and Future Homes Standards in England and Wales.
Resources
Conclusion
The key conclusions are:
1. Timber frame outperforms masonry construction on a whole life carbon basis by up to 5t CO2e per dwelling, equivalent to 16,500 road miles, due to:
- lower embodied emissions of materials
- lower emissions from transport to site
- less energy and time spent on site
- the benefits of carbon sequestration during the life cycle of the building
2. The differentiating factors are the wall elements. The embodied emissions of the timber frames wall elements are up to 82% less than that of the masonry construction. This equates to up to 5t CO2e upfront savings per dwelling, equivalent to 16,600 road miles.
3. The cementitious products generally have the highest contribution to the lifecycle embodied emissions including roof tiles, concrete blocks, brick cladding, strip foundations and floor slabs. However, masonry constructions perform better at end-of-life than timber frame construction, as no sequestrated carbon is released from 10% sent to landfill.
4. A key challenge is the lack of supplier EPDs. Much of the calculation was carried out on an average basis rather than a supplier specific basis. To calculate whole life carbon more accurately, there needs to be increased emphasis on EPDs for key products and suppliers.
Operational emissions are predicted to reduce with the implementation of the Future Homes Standard, continued decarbonisation of the UK electricity grid and increased electrification. The benefits of timber frame over masonry construction will become increasingly significant, as will focus on reducing the embodied emissions from cementitious products.
