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 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 vapour barrier. This helps remove condensation and helps direct water away from the dry insulation where it otherwise might cause problems such as mould formation and water leakage. The Air Vapour barrier prevents water molecules from entering the insulated cavity but allows the passage of air.
The air gap is created using steel hatbars fastened vertically to a series of horizontal spanning subgirts. The hatbars also provide a fastening surface for the facade panels. An EPDM gasket 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 permeable air vapour barrier in between. Behind the air vapour 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 concrete, terra cotta, clay, porcelain, galvanized steel, aluminum, thin stone panels, thin-brick panels and polyurethane.