A rainscreen is the exterior weather-facing surface of an exterior wall detail that stands off from the moisture-resistant surface of the structural backup 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 the same building.

In a rainscreen the air gap allows the circulation of air across the air vapor barrier. This helps remove condensation and helps direct water away from the dry insulation where it otherwise might cause problems such as mold formation and water leakage. The air vapor barrier prevents water molecules from entering the insulated cavity but allows the passage of air.

The air gap is created using  Z and HAT profiles fastened vertically to a series of horizontal spanning subgirts. The vertical Z and HAT profiles also provide a fastening surface for the facade panels. An EPDM gasket can be placed between the facade panels and the hat bars to prevent rain water from entering the ventilation channel created by the vertical profiles. The gasket directs water away and toward special drip edge flashings which further protect other parts of the building.

The vertical Z and HAT profiles are connected to the horizontal subgirts with a permeable air vapor barrier in between. Behind the air vapor barrier, there is often space for different varieties and thicknesses of insulation. The thickness of insulation is determined by building code requirements as well as performance requirements set out by the architect.

​Rainscreens are constructed from many different materials including LAMINATE, FIBERCEMENT, phenolic panels, alucobond panels, concrete, Terra cotta, clay, porcelain, galvanized steel, aluminum, thin stone panels, thin-brick panels and polyurethane.

( *** See Wikipedia )

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