The present paper presents results of a study on hemp-lime composite – a novel building material which is gaining attention thanks to its pro-ecological values, as well as interesting hygrothermal characteristics. The thermal conductivity and vapour permeability tests were performed on composites which varied in terms of composition and density as a result of use of various binders, different proportions of ingredients in a mixture and different compaction level during manufacturing with the use of the tamping method. The results obtained, indicating low thermal conductivity and very high vapor permeability, were tabulated with results of compressive strength obtained in the previous study on the same types of composites. The conclusions emphasise supreme importance of apparent density on properties of material, rather than binder composition – which exerts a significant effect only on compressive strength. The results of the performed tests were applied for determination of external walls’ construction, which were subjected to analysis of risk of interstitial water vapor condensation according to Glaser method. For locations in all Polish climatic zones, no condensation or only a small amount thereof, in which case it does not accumulate in subsequent years, was found.