Abstract Hempcrete is a bio-aggregate based composite material used for building envelopes which typically consists of hemp shiv (hurd), lime binder and water. Hempcrete has several distinct advantages including low thermal conductivity, effective moisture buffering, and high sound absorption, while having a high carbon sequestration “index”. This work investigates the impact of mix proportions on hempcrete properties and the hygrothermal performance of two proposed hempcrete wall assemblies for Ontario, Canada. The experimental results highlight the significant influence of the binder on the density and thermal conductivity of the final material. Thermal conductivity measurements ranged from 0.074 to 0.103 W/mK. Finally, hygrothermal analysis demonstrated that when using hempcrete in the Canadian climate a rain screen wall system is more suitable than a mass wall.