FAILURES
Deborah Slaton, David S. Patterson, AIA, and Jeffrey N. Sutterlin, PE
When detailing a typical punched window opening surrounded by cavity wall construction, head and sill flashing manage bulk water within the cavity. However, without proper detailing of jamb conditions to ensure continuity of an effective cavity closure around the entire window or door perimeter, as required by the International Building Code (IBC), direct ‘communication’ between the exterior wall cavity and building interior is still possible.
Without integration or closure between the exterior wall cavity’s drainage plane and the fenestration (often due to a lack of effective detailing at jamb conditions, either by design, execution, or both), unobstructed pathways can exist for bulk water and moisture-laden air within the cavity to migrate into the building interior, provided there is a driving force to encourage moisture movement. One such force that can have a significant impact on the building enclosure performance and heighten moisture-related issues within the building is pressurization of the building interior relative to the exterior environment.
Buildings frequently operating under a negative pressure relative to building exterior can draw bulk water and moisture-laden air into the building. Under the right conditions, this moisture transport via air movement can result in a sustained wetting of, and eventual damage to, susceptible interior finishes, creating a suitable environment for mold growth.
In the example shown, mold developed on the gypsum board finish on exterior walls of resident rooms in a six-year-old, multi-story, brick-clad residence in the northeast. While there was minor water leakage attributed to the punched storefront windows, a major contributor to the interior conditions was the lack of a cavity seal at the jambs of the openings, exacerbated by the building frequently operating under a negative air pressure.
While the building was designed to operate under a positive pressure during peak loads, the large exhaust requirements of the facility caused a negative level of building pressurization during both moderate and low load periods of operation. Maintenance personnel aggravated this imbalance by shutting down some makeup air units to prevent unconditioned air from flowing into kitchens and the laundry room in the lower floors.
Air from the resident’s rooms was drawn through stairwells and elevator shafts due to the disparity between the exhaust and supply air and the potential influence of stack effect. Therefore, these rooms experienced a negative air pressure relative to the exterior environment, which drew moisture-laden air from the wall cavity into the rooms. The use of vinyl wallcovering for interior finishes further exacerbated the condition by trapping moisture within the gypsum board.
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.
Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois, specializing in historic preservation and materials conservation. She can be reached at dslaton@wje.com.
David S. Patterson, AIA, is an architect and senior principal with the Princeton, New Jersey, office of WJE, specializing in investigation and repair of the building envelope. He can be e-mailed at dpatterson@wje.com.
Jeffrey N. Sutterlin is an architectural engineer and senior associate with WJE’s Princeton office, specializing in building envelope investigation and repair. He can be reached at jsutterlin@wje.com.
