Window Leaks Rampant, Canadian Study Reports

An intensive study of window performance carried out by the Canada Mortgage and Housing Corporation (CMHC) and the British Columbia provincial Homeowner Protection Office (HPO) reported last winter that most if not all windows are prone to significant water leakage. Manufacturing, building design, installation, and maintenance were all contributing factors: More than half of new windows let water get past the operable glazing in factory testing. In on-site quality-control inspections using a different test method, 35% to 48% of newly installed windows were found to leak through the window unit itself, through joints between the window and the rough opening, or both.

The passage of time, not surprisingly, does not make leaks go away. After several years in service, the incidence of leaks rose because of deterioration and wear and tear. Windows in homes performed worse than commercial windows: 100% of installed residential windows examined after years in service were found to leak either through the window unit itself or at points of attachment to the building.

The report draws on data from only a few hundred windows (all made in Canada), and the authors did not identify any window brands. "There are probably a thousand window manufacturers in Canada, and the quality varies widely here as in the U.S.," says Bob Maling, research and education director for the Homeowner Protection Office. "But the observations in that report apply to any company's windows in the U.S. or Canada. Even the best-made window could be damaged during shipping or installation. So designers today should take the approach that any window may allow water through at some time, and you should design the wall to handle that water."