Thermal mass and whole-life carbon

The whole-life carbon of buildings comprises many elements, with the structure and sub-structure  contributing about 25% of the total. This is based on a study looking at a six storey concrete apartment block. The study  also found that when comparing the concrete construction with an equivalent cross laminated timber (CLT) construction the difference in whole-life carbon, was around 6% over a 60 year building life cycle. For low-rise housing, a study by the NHBC Foundation found the difference to be around 1 to 4% over a 60 year life cycle when comparing masonry and timber construction.

With the move towards whole-life carbon assessment, these comparatively modest differences in embodied carbon can now be evaluated in the round, alongside the various merits concrete and masonry offer, which includes good durability, fire resistance and thermal mass. The operational carbon savings that thermal mass can offer are highly project specific, but as the climate continues to warm, it is likely to play an increasingly useful role in reducing the cooling demand in buildings. Thermal mass can also reduce peak space heating and cooling loads, which is beneficial from a plant sizing, cost and embodied carbon perspective, but of greater value is the benefit to the national grid from a reduced peak electrical demand, helping to balance out supply and demand.

This is set to become an important aspect of high thermal mass buildings, which can be actively controlled to store and release heat so their demand profile responds sympathetically to the peaks and troughs of the renewable energy feeding the grid. In this way, the building’s energy demand can be shifted away from periods of high grid carbon intensity – that is, when fossil fuels are needed to meet a shortfall in renewable power; a key objective of Active Buildings. The net result is carbon savings at a grid/national level. For more information see the article Peak performer in Concrete Futures, and also The Concrete Centre guide Life cycle carbon analysis of a six-storey residential building.