December 12th, 2017
Water is the most significant factor in the deterioration of buildings. But walls can be designed to stay dry, or at least to limit wetting through the “4-D” strategies of Deflection, Drainage, Drying and Durability to such an extent that deterioration does not become an issue. This article examines the many considerations that must go into the design of walls that “stay dry,” starting with the results of several CMHC studies that looked at the most common causes of building problems. The sources of moisture that can cause wetting of walls, including interior, exterior and construction moisture, are examined and methods of controlling each source are discussed. This article gives special emphasis to the penetration of rain, as rain is the leading cause of water problems in walls. Several design approaches are discussed for keeping walls dry, including drained cavity walls, simple rainscreen walls and pressure-equalized rainscreen walls. Lastly, environmental data are presented that can be used to determine the severity of the environmental conditions to which the wall will be exposed; such data can be of use in determining what moisture control strategy should be employed.