Technology: The Use and Uselessness of Vapour
How was it possible to build soundly in the past without a knowledge of vapour barriers and their function? External walls were mostly of monolithic construction, and water vapour could normally diffuse through them without causing condensation within the material. If condensation did occur, it was usually small in amount and the material was able to dry out quickly. Even internal insulation (ills. 2, 3) with materials subject to capillary action was unproblematic in this respect. Waterproof membranes first became necessary with the introduction of external walls in lightweight timber-stud or framed construction (ill. 4).
