Masonry Magazine December 2012 Page. 33
Masonry installation
See www.icc-es.org/criteria/pdf_files/AC38.pdf for more information about ICC-ES's "Acceptance Criteria for Water-Resistive Barriers."
SPECIAL CONSIDERATION needs to be paid when applying housewrap to buildings with brick or stone veneers. These types of veneers serve as "reservoir" cladding systems, which can absorb water during rain events and then warm up when the sun comes out. This causes vapor to drive into the wall cavity if the housewrap has a high moisture vapor transmission rate. That is one reason why it's best to steer away from micro-porous weather barriers and, instead, choose one with a non-woven substrate and non-perforated coating of advanced breathable polymers. This type of wrap exhibits superior performance water resistance with the ability to allow vapor to escape from wall cavities. WRBs are not required over actual concrete or masonry walls, only over stud or frame wall construction (per 6.1.5.1 of the 2008 Masonry Standards Joint Committee.)
Nova Wrap, like most of the better housewrap products on the market, can be installed under bricks, stone, stucco, EIFS, rigid foam, as well as wood and fiber cement siding. When working with stone veneers built over wood frame construction, the 2009 International Building Code (Section 1405.6) requires two layers of housewrap or other WRB. IPG recommends attaching one layer of its product to the sheathing and using an additional layer to the exterior side. In other words, the WRB should be separated from the stone and mortar by a second layer of WRB. The first layer, which was applied directly over sheathing or studs, serves as the wall system's WRB and should be integrated with window and door flashings.
Brick facades require a ventilated air space a minimum of one inch between the housewrap and the cladding. It's essential to follow the manufacturer's guidelines regarding the use of an air space between the brick veneer and the sheathing.
As building science continues to evolve, product development specialists are working to create the right WRB products to better help reduce air infiltration, cut utility costs, improve indoor air quality, and increase comfort. The ultimate goal is to help system specifiers, designers, architects and contractors meet sustainability goals for the betterment of the environment. IMAS
David Martin, Ph.D., is product manager, building and construction, at IPG (Intertape Polymer Group), a company that develops and manufactures weather barrier building products including building wrap, roof underlayment, and flashing. For more information, call 800-474-8273 or visit www.itape.com.