Tags: #architecture #ashrae #buildingdesign #buildingscience #hygrothermal #resilience #waterresistance

Visualizing storm events in hygrothermal simulations: the importance of water resistance in extreme weather years.

Here, I’ve simulated a severe weather year (ASHRAE Year 3) which corresponds to 1983 – the same year Hurricane Alicia hit the Galveston-Houston area (August 17-18). I’ve purposely modeled a very vapor open wall assembly configured with mineral wool exterior insulation (1.5″), a gypsum-based WRB panel, and 4″ cavity-filled insulation. The wall is clad with fiber cement and includes a 1-inch ventilated rainscreen cavity. In terms of thermal performance and water resistance, it’s a code-compliant wall. Those who design in this area, know the importance of water resistance, so such an assembly would rarely exist – but it certainly could – and it certainly has.  I’m simply making the point that even the most vapor-open wall will not dry efficiently if inundated with bulk water.

I modeled ASHRAE Year 3 data for Houston with a southeastern building orientation. These simulated conditions, using very real weather data, show that it doesn’t take a hurricane to cause grief to this wall. Major storms in May, and again in September, were more than enough to challenge this assembly. As the hurricane itself, this wall was a disaster.