Words: Michael Radigan
Introduced more than 20 years ago in the United States, rainscreens have become one of the most popular and effective technologies for deterring damaging rainwater intrusion into a building’s envelope.
Often referred to as a “stylish raincoat” for a building, the exposed outer layer of a rainscreen can be made from a variety of materials, including glass, terra cotta, fiber cement, metal, glass fiber-reinforced concrete, wood, fiberglass or concrete. Rainscreen designs often have artistic elements that can help set one building apart from another.
In the most basic of terms, a rainscreen system is the attachment of an outer skin of rear-ventilated cladding onto a new or existing building’s façade. The system is a form of double-wall construction that employs an outer layer to keep out the rain and an inner layer to provide thermal insulation, prevent air leakage, plus carry the wind load.
Buildings with rainscreen systems tend to be more durable and less prone to costly repairs resulting from water damage. In addition to managing water infiltration, rainscreens are also effective at managing air infiltration, wind pressures, heat transfer and vapor transmission into and out of the building.
Essentially any building located in a relatively wet climate with an average annual rainfall of 60 inches or more is an ideal candidate for a rainscreen. Rainscreen systems are required by building codes in some cities, although most buildings could benefit from a rainscreen system, in general. A wall protected by a rainscreen will experience far less damage than a wall facing the elements without one.
The only real drawback of a rainscreen is the added cost associated with its more complex design and installation.
There are essentially three main types of rainscreen systems available today: vented, drained and vented, and pressure-equalized.
This type of rainscreen is not recommended for buildings more than four stories high due to potentially unsafe wind loads. This type of system utilizes a warm cavity that is open only at the bottom and provides a dewpoint similar to the outside, therefore reducing the chance of moisture entering the system.
Drained and Vented Rainscreen
This type of system is not watertight and requires a cavity opening at the top and bottom to provide for drainage and convection ventilation. This system is also not recommended for buildings more than four stories high due to the potential danger of condensation buildup. An overhang is generally specified to protect the cavity from the elements.
This is the only type of rainscreen system that can be built above six stories. It has ventilation openings large enough for air pressure to nearly equalize on both sides of the cladding. Extensive design is required with this system to balance the amount of air flowing into and out from behind the rainscreen panels.
Since rainscreen systems can be complex, facility managers and owners should consult with a reputable specialty contractor experienced in rainscreen systems to determine which type to use.
Michael Radigan is senior operations manager for Western Specialty Contractors –Façades Division in Ridgefield, N.J. For more information about Western Specialty Contractors, visit http://www.westernspecialtycontractors.com.