The design and installation of all cladding systems needs special attention to ensure successful performance during high winds and driving rain, while maintaining a seal around all penetrations, expansion and floor deflection joints. Heavy stucco claddings, common in certain regions of the country including the seismic-prone West Coast, face even greater challenges by placing seismic drift joints across the head of the window or wall system.
Stucco systems are not impervious to water penetration, so maintaining the integrity and weather-resistance of the exterior wall envelope is of utmost importance. Stucco facades consist of Portland cement plaster, metal lath, and a water-resistant barrier (WRB), which serves as the drainage plane behind the outer cladding of the stucco. Typical building paper properly shingled as a backup has been shown not to adequately perform under new building code requirements. Fasteners used in mounting the plaster's casing bead (J-molding) and metal lath penetrate the building paper and may allow air/moisture access while not providing an acceptable connection for the window or wall system.
A continuous backup waterproof drainage plane must protect the structure, while accommodating the forces. To date, no air barrier manufacturer had tested and documented that their products could comply with the 2007 California Building Code, Chapter 14 for Exterior Walls. This requires the wall assembly to pass an extended two-hour water exposure test in accordance with ASTM E331 under 6.24 psf differential pressure.
On the West Coast, air barrier assemblies must be vapor-permeable so Tremco'sExoAir® 230 Fluid-Applied Vapor-Permeable Air Barrier Membranewas applied to keep liquid water out, yet remain permeable to the passage of water vapor so as not to prevent moisture from being trapped in the wall. Its self-gasketing capability, where fasteners penetrated through the membrane, also meant additional detailing wasn't required.
Tremco's stucco wall testing:
With Tremco's Sustainable Building Solutions Test Facility, Tremco is able to develop and test sustainable building solutions for the most challenging applications facing us today. This testing will ensure PROVEN, DOCUMENTED solutions to eliminate the guesswork and help transform today's built environment into a high-performance environment.