On a whole life carbon basis, the Whole Life Carbon Assessment of Homes study predicts that up to 5t CO2e per 4 bed dwelling, equivalent to 16,500 road miles, could be saved when using timber panelised MMC methods.

AIMCH is a £6.5 million collaborative R&D project which aims to promote and develop industrialised off-site modern construction methods to build homes quickly and viably.  Participating partners are Stewart Milne Group, Barratt Developments PLC, L&Q, the Manufacturing Technology Centre (MTC), the Construction Scotland Innovation Centre (CSIC) and Forster Roofing Services Ltd.   

Stewart Dalgarno, AIMCH project director and director of innovation and sustainability at Stewart Milne Group, said: “The comprehensiveness of this report provides valuable insights into where developers, housebuilders and the supply chain can make a positive contribution to reducing the whole and embodied carbon contributions of new build homes.

“AIMCH commissioned the report to understand the differences in whole life carbon emissions over 60 years, to current building regulation standards, between open and closed panel timber MMC systems and aerated concrete blockwork used in masonry construction. All processes relevant to the construction cycle, in line with the RICS model have been considered — materials, manufacture, transport, usage through to the end-of-life and disposal stages. The resulting comprehensive analysis provides invaluable data to inform house builders on the carbon intensity of the two construction methods.”

Using the RICS Standard for Whole Life Carbon Assessment, the report represents a rigorous cradle-to-grave assessment of the carbon impact of both types of construction materials and their respective methodologies. 82% of emissions are generated from the homes operational use over 60 years, which is the same for both methods. 14% of emissions are generated from the materials and construction process. A small proportion of emissions are generated at end of life.  

The study, authored by green energy consultancy Verco, examined four types of homes utilising either: masonry – aerated blockwork and offsite manufactured open and closed panel timber MMC, both with brick cladding.

Areas investigated included:

• Production stage – raw materials, manufacture, transport
• Construction stage – energy, transport, waste disposal during  construction
• In use stage – use emissions, maintenance, repair, replacement, refurbishment, operational energy use
• End-of-life – demolition, transport, waste processing, disposal

Carbon sequestration benefits of timber, in line with RICS protocols, were applied to all methods of construction, for example benefiting masonry homes built with timber floors and roofs. End of life assumptions used identical 90% recycle/re-use and 10% to landfill ratio across both material types.

Cementitious products including roof tiles, concrete blocks, brick cladding, strip foundations and floor slabs, were found generally to have the highest lifecycle embodied emissions. Conversely, timber frame wall elements sent to landfill, were found to produce 0.5 tCO2e emissions at end of life, compared to aerated concrete blocks.

Panelised timber MMC construction methods outperformed masonry construction on a whole-life carbon basis, when comparing the direct substitution of various wall elements – external, load bearing and party wall elements. Embodied emissions of these wall elements being as much as 82% less than that of the masonry construction. In addition, timber MMC key properties contributing to reduced emissions  include:

• Lower embodied emissions of materials
• Lower emissions from transport to site
• Less energy and time spent on site
• Benefits of carbon sequestration during the life of the building

Further research is being conducted, assessing the impact of new building regulations coming into force in June and the Future Homes Standard.