One of the unique features of this new build was the enclosure design. The exterior of the CLSB is comprised of prefinished perforated panels of aluminum, engineered in a corrugated profile. While this specific feature provided the academic building with enhanced visual interest, one technical challenge was wind and water intrusion. It was important the design meets the project’s stringent water intrusion goals. Open-joint cladding systems specifically require extreme water and wind protection. If the WRB is not durable enough to withstand extreme weather conditions or stable when exposed to prolonged periods of UV light, the system will fail. With the CLSB building exposed to strong winds off Puget Sound, the concern was the constant positive and negative pressure of blowing wind could damage the membrane, particularly at fastening points.
Designing the assembly
When determining what would go underneath the panels, it was critical to choose a water-shedding membrane suitable for the conditions in Oregon, as CLSB is situated in an area where high winds and wet weather are common. The team considered using a black sheet metal for the weather barrier, but then looked to a WRB solution that could provide strong weather protection and UV resistance. The neutral black color of the product also provided a suitable background to give the perforated panels the desired visual depth. However, questions arose about durability because of the building height and local weather conditions.
Testing
Special testing was required for the application, as the building is subject to extraordinary wind conditions. As explained, the concern was the durability of the membrane since it would be subject to the cyclic action of wind pressures. The testing was a collaborative effort and was critical to measure the WRB’s structural strength and durability. The testing was done over the span of two days, where the lab put the membrane through 9000 cycles of pressure differential, each consisting of three seconds of pressure followed by three seconds of rest. To fully observe the condition and performance of the membrane, testing was done in increments—7000 cycles with a positive pressure differential of 575 Pa (12 psf), followed by 2000 cycles of negative pressure differential at 575 Pa. Since no test exists for this kind of design previously, the laboratory created a test method that was based on ASTM E1233, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights, and Curtain Walls by Cyclic Air Pressure Differential.
The results of the test showed no measurable wear, indicating that the WRB was quite durable. However, given the severity of the Oregon weather, the team wanted to dig further. Therefore, after the initial testing, the team attempted a five-minute cycle at higher wind velocity pressures, up to 193 km/h (120 mph) and performed destructive testing on the wall system. Rips or tears were not seen on the membrane but the z-girts gave out before the membrane.
For a building with an exterior cladding full of holes, using a suitable WRB proved to be the best solution to preserve the structure’s performance and enhance its aesthetics.
Conclusion
Protecting open-joint buildings from water, wind, and UV is extremely important since they tend to expose the inner parts of the performing walls to extreme weather conditions. The CLSB case study reiterates the importance of installing a membrane that is water- and wind-resistant in open-joint cladding systems. With a durable and effective WRB in place, building professionals can be confident their projects and aesthetic visions are well protected and will be an enduring legacy.
As you state it is critical for an exposed WRB/AB to be; UV stable, water, and wind-resistant, though in most cases a hidden WRB/AB, as in the Life Science Center building’s interior of the insulation peel-n-stick, is used as the primary barrier. The exterior exposed membrane hides the continuous mineral wool insulation and provides an umbrella that limits moisture and air infiltration.
I would add that it is critical that the exterior exposed membrane must be highly vapor permeable to allow diffusive drying of interstitial moisture. This is especially the case for Portland’s zone 4c rainy climate, where discontinuities of the WRB/AB installation provide water intrusion that can be trapped.