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Building Materials in the Operational Phase

Impacts of Direct Carbon Exchanges and Hygrothermal Effects

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Summary

How sustainable are the various building materials, and what are the criteria for assessment? The scope of this article is to explore in what ways responsible and conscious use of materials can yield environmental benefits in buildings. In particular, it discusses how material properties related to thermal and hygroscopic mass can be utilized for achieving energy efficiency and good indoor air quality, and how these gains can be included into the context of life cycle assessment (LCA).

A case study investigates and compares carbon impacts related to three design concepts for an exterior wall: (A) concrete/rock wool; (B) wood studs/wood fiber; and (C) wood studs/hemp lime. The thermal performance of concepts B and C are modeled to comply with concept A regarding both thermal transmittance (U-value) and dynamic heat flow (Q24h) using the design tool WUFI Pro. An environmental cost-benefit analysis is then accomplished in four steps, regarding (1) manufacturing and transport loads, (2) carbon sequestration in plant-based materials and recarbonation in concrete/lime, and (3 and 4) potentially reduced operational energy consumption caused by heat and moisture buffering. The input data are based on suggested values and effects found in the literature.

The summarized results show that wall A has the highest embodied carbon and the lowest carbon storage and recarbonation effects, whereas wall C2 has the lowest embodied carbon and the highest carbon storage and recarbonation effects. Regarding buffering effects, wall A has the highest potential for thermal buffering, whereas wall C has the highest potential for moisture buffering.

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