The field of study is the experimentally justified choice of material for a single-layer, energy-efficient thermal protection of the exterior walls of typical buildings in the subtropics. A decrease in the vapor permeability of the mineral heat insulation at a humidity of more than 50% has been experimentally confirmed, and their loss of heat-shielding properties during moistening has been substantiated. It is recommended to correct the vapor permeability values of external walls with multilayer heat protection with Rockwool due to a decrease in the diffusion resistance coefficient of the wet zone of the material compared to the dry zone. Based on a comparative analysis of the design parameters of the types of thermal protection, it is recommended to use thermal plasters as single-layer thermal insulation systems. The experimentally established value of open porosity of 83.1%, for thermo-plaster based on foam glass, made it possible to choose protection against moisture in the form of penetrating Penetron waterproofing. The use of such protection reduced the value of open porosity of samples to 59.2% and eliminated the effect of condensate on energy efficiency when modernizing existing buildings.