Rain screens protect buildings from rain and weather damage by diverting rainwater. They consist of an outer casing, a vented air cavity, and a watertight support wall. There are two types: simple and pressure equalization. Rain screens are essential for building durability and safety.
A rain screen is used to protect the exterior walls of the building from rainwater and other weather damage. By diverting the intrusion of rainwater, the rain guard system protects the building from moisture problems such as wall leaks and roof leaks. Rain screens typically consist of an outer casing, a vented and drained air cavity behind the casing, and a watertight sealed support wall that is separated from the casing by the cavity.
The rain cladding can be masonry, stone, wood, glass or metal. The force of the rain is diminished by the cladding and the gap behind it reduces the pressure of the rainwater on the retaining wall. The vents in the liner and its generally porous nature allow for good airflow into the cavity and this prevents moisture buildup in the cavity. The airtight support wall, covered with a rigid layer of waterproof material, also ensures that there is no moisture damage to the building.
There are two types of rainfly, simple rainfly and pressure equalization rainfly. A simple rain screen is usually adequate in areas with low rainfall. In this type of rain cover, the liner is vented and the backing wall is airtight and layered with waterproof material. The wall base usually has a flashing and a drain. A good example of a simple rain cover is a brick masonry facing over a cinder block wall.
A pressure equalizing rain screen is more advanced than a simple rain screen and better suited to areas with heavy rainfall. The principle of operation here is that when a storm whips through the building, vents in the cladding allow the air in the cavity to impinge against the air barrier layer of the supporting wall. Air pressure builds up in the cavity and soon this pressure equals the air pressure hitting the liner. As a result of this internal and external pressure equalization, there is no more moisture suction inside.
Such pressure equalization, of course, works more perfectly in theory than in reality, but compartmentalizing the cavity can help to a great extent. The sizing of the joints will also minimize the penetration of rain beyond the cladding. It is important to use high quality, long lasting sealants and drainage layers on the support wall so as not to reduce the efficiency of the pressure equalization system.
Rain screens are quite essential protective features in buildings. Screens help the exterior walls of the building remain durable for a long time and reduce the need for too many repairs. By preventing decay due to moisture, rain filters also make buildings safer.
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