Moisture Management in Masonry Buildings

Unitized flashing provides an integrated design solution
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Sponsored by Mortar Net® USA, Ltd.
Celeste Allen Novak, AIA, LEED AP
This test is no longer available for credit

Advantage of Unitized Flashing Materials

When installed at the base of a masonry wall, flashing spans from the exterior to the interior of that wall. Flashing covers the gap between the masonry and the substrate backup wall or in the case of a single wythe system, covers the open cells in blocks. Flashing should primarily be durable and resist and direct moisture as part of a complete system. Flashing materials should be tough enough to resist puncture by a mason with a trowel as subsequent layers of mortar and masonry are added to the wall. The flashing material should be flexible enough to be formed and placed on the wall. Flashing is adhered to the wall with adhesives that allow for expansion and contraction without cracking during seasonal changes. The flashing material must be compatible with the masonry, back-up substrate wall, adhesives, sealants, air barriers, mortar, salts, and masonry. Flashing materials should not cause staining on the wall and should be almost invisible when placed along the wall surface.

The estimated life of the flashing should match the life of a building. Replacing flashing, particularly in high-rise buildings, is difficult and expensive. Lower-cost solutions for building flashing, for example the use of asphalt-impregnated felts or tar paper, almost always lead to higher replacement and maintenance costs for the building owner.

The advantages of selecting a unitized flashing system are that the design professional will specify a material that:

  • Decreases the probability of improper installation of materials—especially at difficult locations such as overlaps, rough openings, inside and outside corners.
  • Manages mortar damming so water can easily flow out of the wall cavity.
  • Prevents air pressure differentials that can force moisture in the building envelope.
  • Can specify a material that has recycled content to help with LEED® certification.
  • Assists with timely delivery on site.
  • Provides compatible materials and prefabricated components for end dams and corner boots.
  • Is one product instead of five separately manufactured and sourced products.
  • Predetermines overlaps and enhances uniform installation.
  • Avoid excessive labor installation costs of multiple layers of materials.
Composite, Unitized Flashing Chosen for Hampton University

Architect George Faulkner Jr., AIA, senior designer and project architect for the Hampton University Student Dining Facility worked with moisture consultant, Stephen Hentz, P.E., of Hentz Engineering, to detail this important campus building. The dining hall will serve as an institutional focal point that will be located on the shoreline of the Hampton River on the campus of Hampton University overlooking downtown Hampton, Virginia.

The 80,000-square-foot facility will be housed on two levels with the second floor set back from the main façade to create a dramatic two-story atrium along the waterfront. The main floor will house a central dining area with food service kiosks around the perimeter of the atrium. The second floor will house a full-service market-style food court and administration areas. The design will also include exterior eating areas with views of the river. To maximize the benefit of its prime waterfront location, the composition of the building will be designed to accommodate views to downtown Hampton through a three-story convex glass curtain wall that will be the length of the building. The building is also designed to complement the other masonry buildings on this historic campus. A contrast of old and new, reflective and permanent, major building materials are brick, precast concrete, and glass. The building is designed with a canted facade, curved walls, and defined edges between the masonry and glass detailing.

The exterior brick veneer wall system for the dining facility was installed over a 2-inch air cavity with a commercial air and moisture barrier applied to a 5/8-inch fiberglass sheeting backed up with 6-inch or 8-inch steel studs. The veneer is drained to the base of the wall through a unitized flashing system that incorporates a mesh cavity drainage material, membrane flashing, termination bar, and stainless steel drip into a panelized product. The flashing panels were installed and sealed together at the end laps using multiple sealant beads. At termination points in the flashing, pre-molded end dams were utilized to direct water to the exterior of the wall cavity. Due to the varying slopes and curves of the curtain wall system, several custom brick veneer cavity closures were fabricated and sealed to the moisture barrier using flashing membrane tapes and stainless steel for rigidity and long service life.

Controlling water penetration on campus buildings was important when designing a building that is clad in brick, glass, and precast concrete.

Photo by George Faulkner

During construction, site visits were performed to observe the installed components for compliance with the project documents. Working with a moisture proofing consultant, the architect commented that the “choice of unitized flashing was presented by the consultant who had previous experience with this unique product.” This selection is part of the overall requirements to design a long-lasting, permanent campus facility.

 

Unitized flashing systems can be specified using any of the most common flashing materials as a membrane. Unitized flashing has pre-designed laps, screws, weeps, termination bars, drip-edges, and a mortar collection device that meets the requirements of the ASTM E-514 water test. These durable systems are easy to install, particularly for high-rise buildings as well as buildings with numerous changes of materials and wall orientation. New products include roll flashing with a mortar collection system directly attached to the flashing membrane, clean lap spaces, and weeps. This adds to the ease of installation and reduces the cost of labor. In addition, the uniform placement of weeps and the clean edges of the flashing are almost indiscernible on the building facade.

 

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Originally published in Architectural Record
Originally published in November 2013

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