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Keep Water Out with Rain Screens

Rain Screens, Water Intrusion

Today’s tip is about a method that can help facility executives keep their buildings watertight. Called the “rain screen principle,” it basically means being ultra-proactive about possible water intrusion from the initial design. The strategy involves creating an air chamber between the exterior and interior wall, such as in a brick cavity wall, so that, with proper air seals and flashing, any water that penetrates through the exterior wall can be stopped in the chamber and directed back outside through the exterior wall.

All of the exterior wall and roof elements have the potential for water infiltration and must be looked at as a system with interactive relationships and co-dependent potentials for water infiltration.

An example of how the rain screen principle works in is in window design. Frames, typically made from aluminum, expand and contract at a far greater rate than other materials. In time, the seal will deteriorate. Applying the rain screen principle can mitigate this problem. It requires the installation of an air seal between the interior window perimeter and the masonry back-up wall, along with a weep or flashing system at the window sill. Installing a vent tube at the sill through the exterior sealant bead and extending it into the newly created chamber provides an exit avenue for any water that has infiltrated.

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