CAVITY WALL MOISTURE MANAGEMENT
Sponsored by Mortar Net Solutions
MortarNet a Key Component of New KU Pharmacy Building
Challenge: When the Kansas University (KU) School of Pharmacy needed a new building, it tapped Treanor Architects of Lawrence, Kan., to design the $45 million, three-story, 110,000-square-foot structure. Treanor is a leader in designing facilities that preserve natural resources and provide a healthier environment, and the building is designed to standards that would compare to a LEED Silver rating.
Influence: KU School of Pharmacy is one of the top pharmacy schools in the country, and the building needed to reflect the school’s leadership position by providing state-of-the-art classrooms and training labs in a warm, friendly environment that encouraged learning.
Criteria: KU wanted an environmentally friendly, low-maintenance, light-filled building that would reflect the school’s emphasis on good health, would last for many years, and would provide a beautiful addition to the growing West Campus complex.
Solution: Treanor chose a combination of masonry cavity walls and metal panel pressure-equalized rainscreen systems, backed with three-inch, closed-cell spray polyurethane foam insulation to meet KU’s strict design criteria. One of the characteristics of both types of walls is that they can potentially admit water through the face of the envelope, which is not an issue if the walls are designed correctly. The KU building includes a high-quality air and moisture barrier inherent to the insulation system, plus drainage systems designed to get the water out as quickly as possible and allow complete drying. Brick walls, in particular, require careful design. Tiny cracks can develop in the mortar that suck moisture into the cavity through capillary action, and brick is a “reservoir” material capable of holding water. Therefore, Treanor was specific in the detailing of the masonry cavity wall system to assure the walls drained and dried according to design.
|The building features weep holes over each shelf angle at the
bottom (shown) and top of the walls. They allow convective air
movement inside the cavity to take maximum advantage of drying
cycles. Treanor’s Mark Muller says that weep vents at the top of
the wall may admit minimal amounts of moisture in extreme
weather conditions, but with a robust weather barrier in the
cavity, it’s really a non-issue. The superior drying effect they
provide just makes good design sense.
They specified the MortarNet with Insect Barrier mortar dropping collection device from Mortar Net Solutions to assure the weep holes at the bottom of the wall stayed open. The product suspends mortar droppings inside the cavity wall at two levels, and its trapezoidal shape and 90 percent open mesh construction mean water always has multiple pathways to the weep holes. Its patented Insect Barrier provides protection against insect infiltration. Mark Muller, Treanor project manager, says Mortar Net is a unique product. Using it assures you won’t get mortar bridging, so water puddling inside the cavity is prevented, along with the staining, efflorescence and possible structural damage that can go with it. He says MortarNet gives Treanor the confidence that they’re getting the water out of the cavity, where it’s designed to go out.
Treanor also designed the masonry cavity walls with weep vents at the top and bottom of every brick wall between supports, where there are shelf angles. Mr. Muller says they chose this design to provide convective air movement inside the cavity, promoting rapid and thorough drying. To complete the walls, Treanor chose WeepVent from Mortar Net Solutions, a 90 percent open mesh vent product. Mr. Muller says they prefer WeepVent over cell-type products, because the mesh fills the head joints completely, can be removed easily for cleaning, is the least visible of the vent products, and comes in a wide variety of colors that allowed Treanor to match the mortar color.
Mr. Muller concludes, “We design realistically in that we know brick and rain screen walls can admit water, so we detail accordingly to get the water out and to take maximum advantage of drying cycles.”
- 53While the quest for increased R-values has led to dramatic reductions in air movement through building assemblies, it has also reduced their ability to dry when they get wet. In-wall systems allow this moisture to dissipate while maintaining the desired degree of airtightness. One way to create moisture escape routes…