Rainscreen
A rainscreen is an exterior wall detail where the siding (wall cladding) stands off from the moisture-resistant surface of an air barrier applied to the sheathing (sheeting) to create a capillary break and to allow drainage and evaporation. The rain screen is the siding itself but the term rainscreen implies a system of building. Ideally the rain screen prevents the wall air/moisture barrier on sheathing from getting wet. In some cases a rainscreen wall is called a pressure-equalized rainscreen wall where the ventilation openings are large enough for the air pressure to nearly equalize on both sides of the rain screen, but this name has been criticized as being redundant and is only useful to scientists and engineers.
A screen in general terms is a barrier. The rainscreen in a wall is sometimes defined as the first layer of material on the wall, the siding itself. Also, rainscreen is defined as the entire system of the siding, drainage plane and a moisture/air barrier. A veneer that does not stand off from the wall sheathing to create a cavity is not a rainscreen. However, a masonry veneer can be a rainscreen wall if it is ventilated.
Many terms have been applied to rain screen walls including basic, open, conventional, pressure-equalized, pressure-moderated rainscreen systems or assemblies. These terms have caused confusion as to what a rain screen is but all reflect the rainscreen principle of a primary and secondary line of defense. One technical difference is between a plane, a gap of 3⁄8 inch (9.5 mm) or less and a channel, a gap of more than 3⁄8 inch (9.5 mm).
In general terms a rainscreen wall may be called a cavity or drained wall. The two other basic types of exterior walls in terms of water resistance are barrier walls which rely on the one exterior surface to prevent ingress and mass walls which allow but absorb some leakage.
In the early 1960s research was conducted in Norway on rain penetration of windows and walls, and Øivind Birkeland published a treatise referring to a "rain barrier". In 1963 the Canadian National Research Counsel published a pamphlet titled "Rain Penetration and its Control" using the term "open rain screen".
Rainscreen cladding is a kind of double-wall construction that utilizes a surface to help keep the rain as well as an inner layer to offer thermal insulation, prevent excessive air leakage and carry wind loading. The surface breathes just like a skin as the inner layer reduces energy losses.
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