The relevance of cut-stone to strategies for low-carbon buildings

A systemic and configurable model for evaluating the global warming potential (GWP) of cut-stone building materials on the French market is developed and then used to benchmark performances against available low-carbon alternatives (cross-laminated timber (CLT) and slag concrete), for which ranges of GWP allocation models (regulatory and research-driven methods) are used to evaluate underlying uncertainties. Cut-stones stand out for their compliance to three key emission profile criteria in which industrial ecology roadmaps should anchor incentives for material selection: (1) a low margin of uncertainty on GWP values, (2) invariability of GWP magnitudes through time and (3) a high comparative performance with available alternatives. Assuming typically implemented load-bearing wall thicknesses (industry averages of 13, 20 and 24 cm for CLT, concretes and cut-stone, respectively) and high-probability scenarios for all materials, cut-stone assemblies are shown to be 1.43 and 2.73 times less impactful (GWP100) than CLT and slag concrete, respectively. Potential impacts of industrial applications at the parc scale are studied, showing that implementing cut-stone instead of concrete walls on 30% of new French collective housing projects over the 2025–50 period would result in a 2.77 Mt CO2e decrease in the embodied emissions of the parc, against 0.43 for slag concrete and 1.18 for CLT (high-probability).

POLICY RELEVANCE
To ensure rapid implementation and tangible climate benefits, industrial roadmaps for transitioning away from carbon-intensive construction practices require swiftly deployable solutions (minimal research and development prerequisites, and the ability to leverage existing workforce in the construction sector) relying on secure supplies (domestically sourced materials, without intersectoral competition), and with high carbon and biodiversity performances readily monitored and ensured (localised low-impact sourcing  with high extraction rates). With the potential resource and capabilities to specify and use cut-stone in buildings (i.e. widely available limestone deposits; a rich tradition of industrial know-how for the equipment and mechanisation of quarries for mass production; and industry average building typologies (four-storey height) suitable for masonry design), its use could be part of an overall strategy to reduce embodied emissions of buildings and meet France’s climate mitigation targets.