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What is a Rainscreen?

Sonal Panse
Sonal Panse

A rainscreen is used to protect exterior building walls from rainwater and other weather damage. By deflecting rainwater intrusion, the rainscreen system protects the building from moisture problems like wall leaks and roof leaks. Rainscreens typically consist of an exterior cladding, a vented and drained air cavity behind the cladding, and a watertight, sealed support wall that is separated from the cladding by the cavity.

The rainscreen cladding can be of masonry, stone, wood, glass, or metal. The force of the rain is diminished by the cladding, and the cavity behind it reduces the pressure of rainwater on the support wall. The vents in the cladding as well as its generally porous nature allow a good airflow into the cavity, and this prevents moisture from building up in the cavity. The airtight support wall, which is covered by a rigid layer of waterproof material, further ensures there is no moisture damage to the building.

Man with a drill
Man with a drill

There are two types of rainscreens, simple rainscreens and pressure-equalized rainscreens. A simple rainscreen is usually adequate in areas of low rainfall. In this type of rainscreen, the cladding is vented and the support wall is airtight and layered with waterproof material. The wall base usually has a flashing and drain. A good example of a simple rainscreen is a brick masonry veneer over a concrete block wall.

A pressure-equalized rainscreen is more advanced than a simple rainscreen, and more suited to areas of strong rains. The working principle here is that when a rainstorm lashes the building, the vents in the cladding allow the air into the cavity to buffet against the support wall's air barrier layer. The air pressure builds up in the cavity and soon this pressure is equal to the air pressure buffeting the cladding. As a result of this inner and outer pressure equalization, there is no more drawing of moisture inside.

Such pressure equalization, of course, works more perfectly in theory than in actuality, but compartmentalizing the cavity can help to a good extent. Sizing the joints will also minimize the rain penetrating beyond the cladding. It is important to use long-lasting, high quality sealants and drainage layers on the support wall so that the efficiency of the pressure equalization system is not reduced.

Rainscreens are quite essential protective features in buildings. The screens help building's exterior walls to stay durable for a long time and reduce the need for too many repairs. By preventing moisture-related decay, rainscreens also make buildings safer.

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