Hempcrete is a very promising bio-based insulating material with a minor or even negative CO2 footprint and low thermal conductivity. 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. The results of ∼8 months of in situ temperature and relative humidity monitoring for a hempcrete wall are presented along with a documented manufacturing process, and the experiment is reproduced in silico, obtaining good agreement and observations in line with previous studies. Given the scarcity of in situ studies, the presented data could be used as a reference for simulations of moisture and heat transfer in building envelopes that contain hempcrete. Validation for hempcrete as a good insulating material for Latvian or similar climate conditions is also provided. Its high mold growth resistance even at high humidity is experimentally demonstrated. Combined with good water and vapor conductivity, this leads to consistently low mold growth risk as shown experimentally and in simulations.