Hygrothermal performance of hempcrete in a multi-layer wall envelope

Abstract

Hempcrete is a promising self-bearing thermal insulation material, as it has low thermal conductivity and a minor to negative CO2 footprint. It is also believed to be applicable not only in building construction, but also for renovation or additional insulation, since hempcrete hygrothermal properties are compatible with wooden structural elements. To utilize it efficiently, it must be possible to make predictions regarding hempcrete hygrothermal performance and whether it is up to the modern standards — this requires a verified material model for use in numerical simulations. Previously, we have shown that hempcrete by itself performs well as insulation for building wall envelopes, and we have validated a material mode for hempcrete. This study assesses, both experimentally numerically, if hempcrete is suitable for use in multi-layer envelopes. A multi-layered wall envelope of a wooden multi-story building was insulated from the inside with hempcrete blocks. Relative humidity and temperature within the wall, as well as heat flow, were monitored over ∼2 years. The wall envelope was modeled numerically using WUFI. Temperature and humidity dynamics predicted numerically are in good enough agreement with experimental observations. In addition, the mold risk forecast derived from simulation and experiment results agree rather well with actual observations — no mold risk was predicted, and no mold was observed upon inspection. All of this suggests that hempcrete could indeed be used as a part of multi-layer building insulation envelopes, at least for climate conditions sufficiently similar to Latvian.