Building diagnostics expert Mark Williams kept seeing a problem popping up in buildings he visited. Water found its way behind siding, and, with no way to get out, would damage the wall system. That made Williams want to promote a construction method that allowed moisture to escape from behind claddings.
Last December, the NAHB and Williams, of Williams Building Diagnostics in Maple Glenn, Pa., released a report that does just that. Called "Improving Drainage and Drying Features in Certain Conditions: Rain Screen Designs for Absorptive Claddings," it details the basics of designing a rain screen behind siding that may retain water.
This report is just one example of a growing interest in rain-screen technology, which, simply defined, is a type of construction where a ventilation space is placed behind exterior cladding. The space allows wind-driven rain or moisture that gets past the siding to dry out and escape.
The systems have a slew of benefits: They improve indoor air quality, increase energy efficiency, and help eliminate moisture problems. The 2005 National Building Code of Canada actually requires the drainage space, the NAHB reports.
Although rain screens increase a project's material and installation costs, which is slowing its adoption in the United States, some pros are hooked.
"People are starting to realize more and more how costly water leaks can be, and what inexpensive insurance these types of products can be against them," says Chris Yount, executive vice president of Fortifiber Building Systems Group, which manufactures housewrap and other waterproofing products. "If you get a leaky wall that creates mold and rot, the cost for remediation is so high."
Yount says some builders and homeowners hesitate to start rain-screen construction as they struggle in this down economy. But others, especially in high-moisture areas such as those along the coasts, are realizing the benefits.
"People are trying to find the cheapest way to build a house, but I think it's an adoption that will continue," Yount says.
Construction Considerations
Rain screens, which work best with siding made of material that absorbs water, such as wood and stucco, can be made in a multitude of ways with a number of materials.
For example, to create an air space or drainage plane, exterior cladding can sit on furring strips or plastic battens. A few manufacturers make mesh or dimpled products that staple to sheathing to create the vent space. Weather-resistant barriers sit behind these spacers, and the drainage plane vents to the outside. This allows moisture to escape and dry. Products should allow air to escape but prevent insects from entering the system. For example, Cor-A-Vent manufactures SV-3 and SV-5 siding vents to serve this purpose.
Other companies sell complete rain-screen systems, such as GranitiFiandre's porcelain tile cladding with included anchors.
Builders also can use specially designed insulation in rain screens; these provide thermal insulation while also draining water. The offerings help reduce indoor air problems within a home, and they can be continually wrapped, which adds to a home's energy efficiency. The air space itself also insulates, adding more energy savings.
Real-Life Applications
Professionals turn to rain screens for a variety of reasons.
When designing a house for a family suffering with allergies, Stephen Varenhorst of Stephen Varenhorst Architects in Philadelphia used a rain screen with exterior insulation.
"If there is any condensation that may accumulate in the insulation, it does it on the outside of the house," Varenhorst says. "So there is no space for mold or allergens."
Meanwhile, Hans Porschitz, building systems team leader for Bensonwood Homes in Walpole, N.H., employs rain screens to curtail moisture issues.
"The drainage plane allows water that gets driven behind the siding to drain out," he says. "If the boards would be tight to the surface, then the water that would be in there would sit behind the siding and not be able to drain to the bottom. That would cause problems with the siding itself."
Bensonwood installs Huber Engineered Wood's Zip System and Benjamin Obdyke's Home Slicker to complete its rain screens. Home Slicker is a 3-D mesh that creates an air space without the need for furring strips. Porschitz says his company staples the mesh to the Zip System, a wall sheathing with a built-in weather resistant barrier. Then, siding goes on top of that.
Furthermore, Mark Demerly of Demerly Architects in Indianapolis uses rain screens because they give him more design flexibility.
"It provides us with the ability to do buildings with open reveals and shadow lines that we couldn't do before," he says.
But rain screens have a few drawbacks. Porschitz recommends the system for all homes, but some clients find it cost prohibitive. Also, he says installers have to be "a little more careful" when using a mesh product to ensure everything is applied correctly.
Although rain screens cost more than more traditional U.S. methods, they can prevent costlier problems and add green benefits and more flexibility to a project.
"You have to come to the point of what should be the baseline to your cost," Williams says. "If your approach isn't working, then what's the point?"