It’s easy for small amounts of water to enter a home’s wall cavity, both during and after construction. When water evaporates it becomes a gas (water vapor) that needs to escape. If the walls can’t completely dry, a home is more likely to experience mold and rot.
A building material’s ability to let water vapor pass through is called permeance, measured in units called “perms.” There are two ways that the American Society of Testing and Materials (ASTM) measures permeance in its E96 test: Procedure A (desiccant or “dry cup” method) and Procedure B (water cup or “wet cup” method).
Here are some common misconceptions about building enclosure performance and the truths behind them:
TRUTH: “Whether a vapor-control material is 5 perms or 35 perms, the drying rate is usually limited by other materials like the cladding,” says John Straube, a principal at RDH Building Science and an associate professor at the School of Architecture at the University of Waterloo in Canada.
TRUTH: “The house wrap industry emphasizes the ASTM E96 Procedure A or ‘dry cup’ test,” adds Straube. “But the test that’s more appropriate for in-service use of wood-framed buildings is really Procedure B or the ‘wet cup’ test. I have a colleague who says, ‘Procedure A measures how much water vapor passes through when there isn’t any water vapor, while Procedure B measures how much passes through when there is water vapor.’”
TRUTH: It defeats the purpose of an air/water barrier if a home’s exterior flashing isn’t done properly. “There are far greater mold risks when sheathing gets wet after the home is occupied than when it’s being built,” says Straube. “If windows leak into the wall, that’s really scary because you can’t see it.”
Learn more about the LP WeatherLogic™Air & Water Barrier system, the latest addition to LP’s portfolio of structural solutions.
Homebuyers are quickly realizing that there’s a new symbol of excellence in energy-efficient homebuilding: the Zero Energy Ready Home (ZERH) certification from the U.S. Department of Energy DOE. Currently only select builders meet the levels of excellence and quality required for ZERH certification – but their numbers are growing as homebuyers learn more about the program.Continue Reading
About half of America’s would-be homebuyers are Millennials, but many have postponed their first home purchase because of sizeable student loan balances and lifestyle choices. However, there are clear signals that more Millennials are now ready and willing to take on a home mortgage. That’s especially true in metro areas that rank high on WalletHub’s “Fun Index,” U.S. News & World Report’s “Quality of Life” index, and Meyers Research’s “Housing Availability” metric. According to the real estate market analysis, there were seven metro areas where building permits grew by 15 percent or more last year, including Orlando, Houston and Minneapolis.
Why the “Field Verify” Approach Can’t Last Forever Last year LP invested $45 million in Entekra, one of the nation’s leading off-site homebuilders. As this type of construction gains popularity in the U.S., a number of architectural firms have asked Entekra to do presentations about how to successfully design for off-site homebuilding.