Ensuring Proper Drainage

With all cladding types, Building Teams must ensure that envelope assemblies are properly designed to drain water so that the wall can fully dry. “One of the most common problems we see is that non flanged windows, which frequently require a watertight seal at the outside face, are instead detailed with a seal to the cladding,” says Altenhofen. “This allows for air and water penetration around the sides of the frame.” Detail the wall to ensure a seal between the window edge and watertight air membrane. This may require some extra sheet metal trim or blocking.

Construction Consulting International’s Blackburn also recommends clearly specifying the size and spacing of the drainage and ventilation weeps, both horizontally and vertically, and indicating the continuity of the drainage plane waterproof membrane, and its seal- ing to the various flashings at the wall base, penetrations, fenestrations, and terminations.

Finneral adds that through-wall flashings should be placed above all wall openings, at all horizontal veneer supports, at horizontal material changes, below window sills, and at the base of exterior walls. “Flashings are generally two pieces, exposed and concealed, which overlap and are sealed to each other within the cavity,” he says. “The inner flashing passes through the insulation and is stripped into the wall membrane with a strip of membrane material. All flashings are set in sealant and weeped above.”

When working with brick veneer, Kabza, a member and past chair of the AIA MasterSpec Architectural Review Committee and founder of Charlotte-BEC, recommends cleaning the air spaces with bottom and top vent holes, not just the weepholes, to reduce efflorescence, promote drying, and reduce inward vapor pressure, especially in humid climates. In addition, transition flashings between the panel-clad wall and brick veneer always require careful detailing.

Considering the wall assembly within the greater context of the building envelope, Sue Klawans, Gilbane’s VP and Corporate Direc- tor of Operational Excellence and Planning, points out that while water flows down the cavity, wind and storm events drive water uphill. This phenomenon can exert pressure to drive water into the interior. Buildings’ HVAC systems are often balanced for negative pressure, which could tend to exacerbate this process. Building Teams should follow a comprehensive building envelope success checklist, including flashings, air and vapor barriers, connections at dissimilar materials, HVAC design intent, end dams, connection to roof, and connection to the foundation.

“Our checklist is extensive, and it’s a good reminder that an exterior envelope is a system just as complex and crucial as the HVAC system or power system,” Klawans says.