Moisture Transport in Walls: Canadian Experience

Canada Mortgage and Housing Corporation, the Canadian federal crown corporation responsible for federal housing policy, has been studying moisture problems in houses for several years. That study has usually been at the system level, that is, looking at the interaction between subsystems, components, and materials. It has spanned a wide range of regimes, from development of theory and a computer model, to laboratory tests on materials and walls, through test hut design and monitoring, to field surveys.

The published theory has been found wanting, in many cases. Designers, builders, inspectors, and material suppliers or manufacturers seem unaware of much that is known. More must be learned about the interactions that take place between energy, air, and moisture flows—over the full range of material moisture contents and air relative humidities and temperatures.

A systems model of the movement of heat energy, air, and moisture, in wood frame walls, is being developed and executed on a microcomputer. That program, named WALLDRY, will be made “user friendly,” then compared with field and laboratory data, but is primarily a research tool, and will likely remain too slow to be used as a regular design aid.