April 27, 2007

Window Performance

Common sense approach reduces water infiltration

DAN O’REILLY

correspondent

A Quebec-based building envelope consultant has a common sense approach for those whose aim it is to reduce water infiltration.

“The building envelope is the skin of the building that prevents air, moisture and heat from flowing freely in or out,” said Mario Goncalves, president of Patenaude-Trempe and manager of the Quebec Building Envelope Council.

That skin is vulnerable to incredible pressure, including air infiltration, condensation, and especially water infiltration, which is the primary source of building envelope problems.

Some of the common causes include poor design, poor construction and lack of maintenance, he said.

“All windows will eventually leak,” said Goncalves, pointing out that architects, designers and other envelope professionals should demand that the performance levels for new or replacement windows be based on the CAN/CSA A440-00 Canadian standard.

“Everyone (in the building envelope business) should have a copy of those reference standards and read them.”

The principal performance levels include: resistance to air leakage (A rating); resistance to water penetration (B rating); wind load resistance (C rating); and condensation resistance (I rating), he said.

PATENAUDE-TREMPE

A full-scale field testing facility allows the company to examine the building envelope in "real" conditions.

Not only is it critical that the sample window tested in the laboratory be representative of the size and configuration of all windows to be installed in the building, architects and designers should ask for the full lab report with appendixes and not settle for a summary version. “You want to know what was tested.”

When it comes to on site tests, it’s not practical to conduct tests on every window, especially on large commercial and institutional buildings that may have as many as 1,500 windows, he said.

But envelope consultants will conduct tests on a random selection of windows on different areas of the building. These tests should be conducted at the beginning of construction, at the mid-point and when the building is completed to avoid costly delays and possible legal disputes.

“Don’t wait until construction is finished.”

In existing buildings with air/water infiltration problems, field-testing can be undertaken as a forensic tool in order to identify the source of air leakage or water infiltration and validate corrective measures, prior to undertaking costly repairs, said Goncalves.

As an example, he cited an institutional building in Montreal. The owner spent $300,000 replacing a roof and other components to eliminate water infiltration. His firm was called in and traced the source to a defective windowsill.

In addition to window tests, building envelope performance can be evaluated by measures such as curtain wall tests, smoke tests, and infra-red thermography.

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