When housewrap was first introduced to the home building industry in the late 1970s, its purpose was to prevent air movement through the wall cavity and to allow moisture vapor to escape. Over the years, moisture damage has become a more prevalent problem, and concerns over preventing mold and mildew—especially in the wall assembly—have increased. Moisture management is now a top priority for many builders.
Housewrap manufacturers have responded by engineering their products for a much-expanded role. “It's not a function of the air barrier aspect becoming less important so much as the moisture management aspect becoming more important,” points out Dan Partrich, marketing manager for Pactiv Building Products.
Bulk water intrusion—water that gets under the siding from sources like wind-driven rain and lawn sprinklers—is now recognized as the main cause of water damage to wall systems, not water vapor. So preventing water that gets past the siding from infiltrating through the sheathing into the wall cavity is increasingly important.
Over the past three years, several housewrap manufacturers have taken an aggressive approach to moisture management by incorporating drainage paths into their products. “Providing some sort of drainage path built into the house-wrap itself allows water to quickly escape the wall cavity,” says Mike Coulton, business development manager for Benjamin Obdyke.
Features such as embedded threads, dimples, or wrinkles in the housewrap form a drainage plane and direct bulk water to the bottom of the wall assembly. Not only do the drainage channels create a space for water to run down the surface of the housewrap, they also create a bit of space for air to move between the siding and the housewrap to aid drying, some manufacturers claim. Benjamin Obdyke and BBA Fiberweb have taken a slightly different approach from other manufacturers and have combined their two primary weather barrier products, creating a two-layer, two-function, single-application product. This product creates a larger space for air movement, they say, because the Benjamin Obdyke matrix is slightly more than ¼ inch thick.
