“Folks on the coast thought [the drainage requirement] was overreaching,” says Doug Lethin, the owner of a Salem remodeling company and one of the members of the Residential Structures Board. “It’s not a cure-all. They’re already taking the steps necessary to prevent water from getting in.”
Chuck Bergerson, a veteran coastal builder who now manufactures wood doors and windows in a small plant in Hammond, Ore., notes that area builders are particularly dubious about modern housewraps. “Some of them tend to trap moisture,” he says. The regional material of choice has always been 30-pound felt, which Bergerson describes as both thicker and more flexible than the 15-pound version. “It seals better around nails, and it doesn’t end up full of holes if you fasten it with a hammer tacker,” he says.
In addition, Bergerson says, builders along the coast use pan flashings at doors and windows and routinely back siding butt joints with tabs of felt to resist water penetration. “Why would we want to change what already works?” he asks.
Rogers concedes that builders like Bergerson have a valid point. “They’re absolute believers in asphalt felt, and I can see why,” he says. “They do it right without a gap and have had no problems.” Just the same, he defends the new drainage mandate. “Rain-screen is obviously best practice,” he says.
Hard to explain. Rain-screen siding makes intuitive sense. But as the Oregon example — and countless long-lived traditional siding applications elsewhere — makes clear, it’s not the only right way to do the job.
“Like a lot of building science, it’s pretty much unproven,” say Paul Fisette, a professor of building materials and wood technology at the University of Massachusetts. “I don’t know of any studies comparing rain-screen siding to conventional siding in any meaningful way, and I can count the people who can explain how it works on the fingers of one hand.”
Some attempts to clarify the science behind rain-screen siding are as likely to confuse as enlighten. A technical article on the NAHB Research Center’s ToolBase .org website, for example, informs readers that “pressure-equalized rain screens, or PER ... terminate the pressure differential across cladding systems that are magnified by winds. This effectively eliminates the remaining moisture force affecting rain screens. PER systems employ barriers to compartmentalize the air cavity, thereby allowing rapid air-pressure equalization and minimal moisture intrusion. This limits the opportunity for rain penetration beyond the cladding.” The article has better luck in explaining the principle behind what it calls “simple rain screens,” which it compares to the familiar example of a brick veneer wall with weep holes.
Given the complexity of any explanation that raises the pressure issue, even builders who use rain-screen siding tend to stress the common-sense aspect and go easy on the science. Seattle builder Kyle Keever has done several rain-screen siding jobs recently but says he makes no special effort to sell customers on the idea. “It does cost a lot more,” he says. “I think that both [conventional and rain-screen siding] can work if they’re done correctly. Most people already know what they want by the time they come to me.”
Mark Parlee, a residential contractor in Urbandale, Iowa, calls rain-screen siding “a very good thing” but notes that he seldom has occasion to use it. “If I were going do rain-screen more, I’d have to figure out how to present it to customers, and I’m not sure how I would do that,” he says.
Newton, Mass., remodeler Paul Eldrenkamp has been working with rain-screen siding regularly for more than 20 years, most often using strips of half-inch plywood as furring. He believes that it’s not necessarily important to provide continuous vertical drainage channels, having had good results laying wood shingles over closely spaced horizontal furring strips. “As long as you have a good moisture barrier under the furring, the small amount of moisture that gets through the shingles will find its way out,” he says.
Both Eldrenkamp and his customers have been pleased with the results. “I’ve never seen peeling paint over a rain screen,” he says. Even so, he views the method less as an upgrade than as an admittedly pricey form of insurance. “It might be belt and suspenders,” he says. “As far as rain-screen goes, we have two kinds of customers: those who know what it is and want it, and those who don’t know but use it because they trust our judgment.”