Durable buildings deflect rainwater from their walls and allow any surface moisture that accumulates to evaporate as the weather dries out. In our designs, we provide a 1-inch airspace for maximum durability. 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 rainscreen system allows the cavity between the exterior veneer and water barrier of the wall to breathe, dry out, and drain to the exterior. This is part of designing a healthy building—this cavity will help combat mold, rot, and leaks.
Mold pollution is the growth of molds in a building resulting in damage to or the destruction of the structure itself (or its contents) and adverse health effects on the building’s occupants. It is estimated that about 10% of U.S. buildings may have mold pollution. To avoid potential health problems due to mold or rot, prevention is key.
Research at the University of Waterloo in Ontario by Dr. John Straube and his team of scientists has shown the benefits of using a 3/8-inch to 3/4-inch venting rainscreen. The data show a significant increase in drying potential versus a conventional wall with simple building paper and no ventilation space. Based on this and other research we can conclude that a ventilated rainscreen accelerates evaporation of undrained moisture behind cladding materials nearly three times faster than without ventilation. It is important to note that a majority of the moisture will drain from the wall system when an effective drainage plane is used. This is in combination with the accelerated drying times with vented wall systems. Other studies by Mark F. Williams with Williams Building Diagnostics show that vented rainscreens are the best method we can use to ensure long-term performance and durability.
Health and / or Social Benefits
Mold pollution in buildings may result in adverse health effects including infections, allergies, asthma, bleeding, memory loss, and a condition known as sick building syndrome. When health effects from molds occur, it is generally as a result of inhaling mold spores. Careful attention to removing spores from the air and water may be the best method to protect the public from these kinds of infections. Including rainscreen technology for your home or building can prevent possible health problems for those using the structure, and particularly for high-risk occupants such as school children.
Most moisture shedding and mold avoidance techniques are low or no cost; they merely require proper detail specifications by the architect and attention to detail by the builder during construction. Proper care during construction is much more cost effective than having to remove roof or wall assemblies to fix moisture problems like mold or rot.
Why Rainscreens Are Required on Oregon Residences and How They Are Good For Your Home
Examiner.com Website, September 2010
EcoBuilding Pulse Website, February 2011
Green Building Guidelines (PDF)
Build It Green Website, 2011
Pollution Issues Website
U.S. Environmental Protection Agency Website