Moisture Content and Heat-Insulating Properties of Building Materials

Abstract

Is the effect of moisture content on the heat-insulating properties of building materials sufficiently taken into account? It is generally known that moisture has a detrimental influence on the effectiveness of all insulating materials. Therefore, an allowance for safety is added to the thermal conductivity value obtained from tests of materials in the dry state. Insufficient knowledge of the moisture content which actually exists in a building material, and lack of a sufficiently large number of results obtained from tests under different moisture conditions have shown that there is still great uncertainty concerning the margin of safety to be allowed. It is also very difficult to obtain a definite value for the thermal conductivity of a building material with a given moisture content. Care must be taken that the distribution of the moisture content during the test is the same as that of the material in use. In the method used at present in Sweden (the material being tested between two metal plates at different temperatures), this requirement is hardly ever taken into account. According to the &dquo;theory for cold walls;’ the moisture passes over to the cold surface of the material where it accumulates in front of the metal plate, while the rest of the material more or less dries out, depending on the time required to attain steady state