| Introduction
"Moisture penetration in walls, from exterior or interior sources, can have significant negative impacts on the durability of housing. A study completed for Canada Mortgage and Housing Corporation (CMHC) in 1996, found that houses in the coastal region of British Columbia (BC) were experiencing substantial problems due to water leakage from exterior sources. In 1997, reported water leakage problems caused similar concerns in Alberta.
As a result of the concerns, the Alberta Housing Industry Technical Committee, representing Alberta's residential construction industry, along with CMHC jointly sponsored a study to: investigate a representative sample of dwellings with various types of windows and wall claddings; draw conclusions on the sources and causes of moisture-related problems through walls and windows in Alberta; make recommendations to remedy the problems; and recommend changes in construction practices to avoid similar problems in the future.
Additional objectives for the study were to: analyse and correlate water entry problems with design and construction features of building envelopes; and compare the nature and cause of moisture problems in Alberta with those found in coastal BC.
Research Program
Data was collected for forty-one houses and nine multi-unit buildings located primarily in Calgary and Edmonton. All buildings were ten years old or less.The specific buildings were chosen because they were representative of typical materials and methods used in single family and low-rise multi-family wood frame houses in Alberta including:
claddings (stucco, vinyl, brick or aluminum siding);
windows (PVC or aluminum clad wood frames with perimeter nailing flanges or wood with brick moldings);
sheathing (oriented strand board or untreated exterior grade plywood);
sheathing membranes (ordinary building paper, spunbonded polyolefin housewrap, or perforated polyethylene sheet housewrap); and
wall construction methods (140 mm framing with glass fibre batt insulation, poly vapour barrier, and gypsum board air seal).
The selected buildings also were classified as problem (those who have or previously had problems), non-problem (proved to not have problems upon inspection) or unfinished (under construction).
Each building review included data collection and onsite inspections.Worksheets, modelled after the BC study, were used to gather information about the general building, wall assembly, wall details, symptoms and failure mechanisms.The onsite research was comprised of a meeting with the building manager, owner or tenant, an inspection of typical moisture-related damage on the interior and a visual inspection of selected exterior locations to determine probable moisture sources and verify construction details.
Informal interviews with building industry representatives were also conducted to gain a better understanding about perceived moisture-related problems.
Results
The buildings that were reviewed were not a random sampling.The selection was biased toward houses that have more problems overall, compared with the entire Alberta housing population.
Exterior Moisture
Exterior moisture, most often from direct rain penetration, was a contributing factor in 91% of problems. Most problems occurred at window and door perimeters and decks.
Interior Moisture
Condensation moisture, caused by occupants trying to maintain indoor humidity above 30% during the winter, contributed to 14% of all problems.
Responsibility for Problems
Construction and design, especially for stucco clad walls, were the most common factors contributing to problems.
Additional Findings
Stucco-clad buildings had more reported moisture problems, compared to vinyl-clad buildings.
Some construction details were disproportionately associated with problem walls including parapets at roof edges, soffits that slope down to a wall, exposed columns, vertical transitions, rail attachments and scuppers.
Moisture-related damage to buildings in the Alberta study was less severe than in the buildings from the BC study, due to less rainfall and greater drying potential.
Walls exposed to the north and west prevailing winds were more likely to experience water leakage. | 
