The paper presents the results of experimental studies of thermophysical characteristics of autoclaved aerated concrete with density of 400 and 500 kg/m3 . The dependence of thermal conductivity on temperature and humidity was determined. The boundary humidities were set for which ice is either not formed or its amount is negligible in the pores of the materials at the temperature below zero. The new method of non-isothermal liquid transport coefficient determination was suggested. It was found that one of the basic mechanisms of moving water for cellular concrete samples with a moisture content over 30 % by weight is non-isothermal liquid transport. The effect of humidity on durability of exterior walls is estimated according to cellular concrete frost-resistance tests.