As far back as 2005 the practice of sealing the weather barrier of a house to the frame of the window in an effort to control moisture penetration was questioned enough to justify 7 years of research at the IRC (Institute for Research in Construction) of the NRC (National Research Council of Canada). The guiding light that came out of that detailed scientific research was: “Don’t try to stop the wind and the rain on the same plane.” Few people paid any attention. But the evidence is growing to change things, while residential windows still rot.
2020 NBC requirements to drain the sill and break the air-tight continuity of a face-sealed wall. The CSA A440 committee has opened the door to alternatives to face sealing, and A440 changes out for review soon will go further. The influential building scientist Joe Lstiburek is proposing pressure-equalized window profiles, and Jon Eakes is working to complete the unfinished work of the IRC in proving in the lab that pressure equalization can be applied specifically to the window/wall interface.
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