Let's face it, housewrap—the thin sheet of material that goes between the sheathing and the siding—won't save you money or help you sell houses. In fact, if you ditched the housewrap you'd probably save yourself some cash up front. But omitting the product would be a really bad idea, because that thin layer is one of the most important things protecting your house from moisture—and you from unnecessary headaches or, worse, potential legal problems.
Housewrap has a simple yet vital job to do: It keeps water away from the house and is the first line of defense in the battle against moisture. “Housewrap continues to be one of the best investments a builder can make for themselves and their home buyers,” says Bob Dahl, marketing director for the Typar housewrap brand at Old Hickory, Tenn.–based Fiberweb. “The Department of Energy has demonstrated that the use of a housewrap can provide 25 percent to 40 percent savings a year on energy costs in a typical home. Given the increasing costs of energy and the desire by consumers to select products that help them conserve energy, housewrap certainly fits the bill.”
Housewrap also lets the house breathe from the inside out, which is an important part of managing moisture. “Normal daily activities inside a home—showering, cooking, washing clothes and dishes, even breathing—produce moisture vapor which needs to escape,” says Jeff Van Sloun, business manager for insulation at Toledo, Ohio–based Owens Corning, maker of PinkWrap. Sloun says his company's product is specially engineered to stop air infiltration while at the same time allowing excess moisture to be “exhaled” so it doesn't build up in the walls. Other good housewrap products perform the same task.
Housewraps can be either traditional heavy building paper or of the nonperforated or perforated variety. According to market research and consulting firm Frost & Sullivan, perforated housewraps can be either woven or laminated polypropylene film having microscopic punched holes for better breatheability. They're generally inexpensive compared with nonperforated housewrap, which is either spun-bonded polyethylene or fiber-mesh–reinforced polyolefin, Frost & Sullivan says on its Web site. The structure of these materials enables water vapor to pass through but inhibits air infiltration. Manufacturers such as Wilmington, Del.–based DuPont, which produces Tyvek housewrap, offer a wide variety of types for different applications and different needs.
Despite all the good things about house-wrap, however, there are problems. For one thing, a lot of builders aren't using it. Sloun says, for example, that “approximately 40 percent of new homes are constructed without housewrap. This is mostly in areas that have not adopted the latest building codes.” On top of that, many builders who are using housewraps are installing them improperly, so they're not getting the full benefits of the system.
“The basic concepts with these products are that they should always be installed in a shingle lap fashion and have enough space to drain moisture down and out to the exterior,” says the report “Water Management Details: Housewraps/Flashing/Windows,” by Building Science Corp. in Westford, Mass. The concept is simple, according to the report, but poor construction methods and details have interfered with the performance of the products.
Typical housewrap problems appear at window intersections and roof-wall connections, Building Science writes. In addition, prolonged exposure to wind and debris often damages the wraps before the cladding is installed. Moreover, cladding installed directly up against the housewrap, without adequate airspace in between, will hold water against it. “In some cases, wood siding bleeds onto the wrap causing it to lose its effectiveness.
Fortunately, these problems can be easily resolved. First of all, use housewraps correctly. Reduce the amount of time your housewrap is exposed to the elements, and make sure it's installed tightly against the sheathing. Wherever possible, install siding with a space between the walls or back-prime or back-coat wood siding to minimize contamination to the house-wrap. If you do these things, you'll give your houses a better chance to remain high and dry.