Testing Building Assemblies for Moisture Resistance
A state-of-the-art testing facility shows that liquid-applied WRBs outperform taped housewrap
When I was in Portland, Oregon, the week before last for the Living Future Conference, I had an opportunity to visit a facility in nearby Clackamas where building assemblies and components can be tested for water intrusion and water vapor penetration.
One of the high points of being a researcher and writer is the opportunity to visit really cool manufacturing and research facilities, so I usually jump at the opportunity to visit something new. I wasn’t disappointed on my recent trip.
Prosoco is a leading manufacturer of liquid-applied water-resistive barriers (WRBs), which can be thought of as spray-on Tyvek, flashing, and tape. Prosoco developed the Clackamas test facility with partner company, Building Envelope Innovations (BEI). Prosoco was at the Living Future conference because of the company’s commitment to sustainability and transparency in building products, and company president David Boyer and sustainability director Dwayne Fuhlhage invited a number of us out to Clackamas to learn how they test for moisture resistance.
A Cat 5 hurricane in a closed chamber
At the Clackamas test facility, Building Envelope Analysis (BEA) — a joint venture between Prosoco and BEI — has two specialized test chambers that can be used to simulate weather conditions as well as more insidious humidity conditions that can drive moisture into wall assemblies or damage building components like insulation and sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .
Along with a half-dozen other Living Future conference attendees, I watched as the submarine-like glass doors of the large chamber were closed and the fury of wind and driving rain were cranked up on the controls. We could see on manometers just how much pressure the wall assembly was having to endure, and we could watch high-pressure nozzles spraying high-velocity streams of water at the assembly.
The operator can turn a few dials and simulate 150 mph wind and driving rain, wreaking havoc on the wall assembly constituents.
David and BEI director of operations Tom Schneider explained how the test chamber can easily be configured to test everything from plywood sheathing and flashing systems, to windows and weather-barrier tapes.
When we visited, a high-tech European window that had been submitted by a local PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. builder for testing was blocked off, because it had failed so miserably that we would have had water all over the place if it hadn’t been sealed off.
Prosoco’s interest in all this testing
We didn’t get into too much detail about building the test chambers, but it appeared that hundreds of thousands of dollars had gone into designing and fabricating them. Why would Prosoco and BEI go to all this effort and expense?
Because BEI developed and Prosoco manufacturers liquid-applied WRBs for building assemblies, and the companies want to show off how much better they perform than more-common WRBs (like Tyvek or Typar) and specialized building tapes, such as those made by 3M, Dow Chemical, Zip, SIGA, Pro Clima (the latter of which we used on our house).
The bottom line is that the liquid-applied WRBs, such as Prosoco’s R-Guard Cat 5 Air and Water-Resistive Barrier, do a lot better than the more common taped membrane systems. While one can question how accurately the test chamber simulates real conditions, the demonstration was compelling.
In addition to the large test chamber for testing whole wall assemblies and components, there was also a smaller chamber used for testing the permeability (or vapor diffusionMovement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough. ) of specific materials — like plywood and WRBs.
With this discussion, I was fascinated to learn that the standard methods we use to measure the permeability of different materials to water vapor are grossly flawed. David explained that the permeability of a material that has a listed perm rating (based on standardized ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. test methods) of 36 may drop to a perm rating of only 2 when that material gets damp from high humidity.
Prosoco and BEI have even more sophisticated test chambers in Florida and Kansas. In addition to testing the effects of wind and wind-driven rain, the Florida facility, which I’m hoping to visit sometime, can test resistance to sudden flood or tidal surges of three to four feet.
With growing focus on resilience and adaptation to climate change, dealing with storm surges in low-lying coastal areas will become more and more important.
Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed.
- All photos: Alex Wilson
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