|This article's factual accuracy is disputed. (July 2013)|
A rainscreen is the exterior weather-facing surface of an exterior wall detail that stands off from the moisture-resistant surface of the main exterior wall. The rainscreen is the first interruption between conditions that exist on the outside of a walled building and conditions that are required on the inside of a walled building. A veneer that does not stand off from the moisture-resistant surface of the structural backup wall to create a cavity is not a true rainscreen. However, a masonry veneer can be a rainscreen.
In a rainscreen the air gap allows the circulation of air across the air (or weather) barrier. (These may or not also serve as a vapour barrier, which can be installed on the interior or exterior side of the insulation depending on the climate). This helps helps direct water away from the main exterior wall which in many climates is insulated. Keeping the insulation dry helps prevent problems such as mold formation and water leakage. The vapour-permeable air/weather barrier prevents water molecules from entering the insulated cavity but allows the passage of vapour, thus reducing the trapping of moisture within the main wall assembly.
The air gap (or cavity) can be created in several ways. One method is to use hatbars (or hat channels, of steel fiberglass, or other materials) fastened vertically to a series of horizontal spanning subgirts. The hatbars also provide a fastening surface for the facade panels. A gasket or membrane, of EPDM or similar waterproof material, is placed between the facade panels and the hatbars to prevent rain water from entering the ventilation channel created by the hatbars. The gasket directs water away and toward special drip edge flashings which further protect other parts of the building.
The hatbars are connected to the horizontal subgirts with a vapour-permeable air/weather barrier in between. Insulation is often provided beneath the barrier between the sub-girts. The thickness of insulation is determined by building code requirements as well as performance requirements set out by the architect.
- Pressure Equalization in Rainscreen Wall Systems, National Research Council of Canada. Retrieved 2013-12-01
- The Rainscreen Principle in Design, National Research Council of Canada. Retrieved 2013-12-01
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