Housewrap backs up both siding and stucco

II/HETHER the walls get siding or stucco, a quality Y V housewrap can vastly improve their weather and water resistance, especially in coastal areas prone to winddriven rain and in climates where secondary moisture protection is desirable.

With siding, many manufacturers recognize the importance of a quality housewrap beneath their products. "If you look in their installation instructions, more of the leading siding manufacturers are specifying the use of housewrap with their siding products," says Rick Schlehofer, Weyerhaeuser specialty building products manager.

Housewrap seals cracks and seams in exterior sheathing, shielding homes against energy-robbing air infiltration, helping wall insulation achieve its full-rated R-value in all seasons. Products such as Weyerhaeuser's ChoiceWrap can be applied directly to studs or over plywood, OSB and foam insulated sheathing. High contact clarity makes locating framing members quick for easy installation. Products also are puncture-resistant, making installation easy with fewer holes to repair.

As for stucco, housewrap may be one solution to recent leaking problems surrounding both traditional and synthetic stucco construction, according to DuPont, manufacturer of a new specialized StuccoWrap housewrap.

Southern California stucco contractor Ron Webber, Prime Plastering, has spent the last several years researching why rain leakage problems didn't exist 10, 15 or 20 years ago. "There also seem to be more cracking problems than there were before," said Webber.

He suspected some of the field problems he had seen could be attributed to changes in the way stucco has been applied over the last 15 years. After extensive testing with a committee of plasterers, manufacturers, product representatives and a residential developet Webber concluded that clean, washed plaster sand is important to a denser stucco base coat with fewer voids, moist curing is critical, and that water will penetrate stucco through cracks, voids and air spaces in the walls.

"There are two reasons for cracking," said Webber. "First, cracks are caused by normal shrinkage of the mortar as the water evaporates from the wall. Second, physical,. forces on the wall are inevitable from plywood shear warping, green or wet lumber shrinkage, excessive loads on outside walls, or walls that are not tied in."

Recent testing by DuPont comparing building paper with StuccoWrap revealed that the housewrap dramatically reduced cracking in the scratch coat. The building paper drew moisture out of the mix too quickly and as the wall cured, the building paper shrank, putting pressure on the back side of the stucco.

"The definition of good quality stucco is density with no voids or air spaces," said Webber. He explained that stucco is extremely fragile and vulnerable during the frst two hours of curing: "When excess moisture evaporates from the mixture too quickly, that's when voids or air spaces are created. And when the wall dries too quickly, the stucco hardens, but does not develop density." The housewrap, though, didn't move during curing, providing a softer cushion during the critical early curing stage.

"Many of the problems I've seen in the field are not because of the systems, but because the systems were not applied correctly," said Chuck Grimes, Grimes Stucco Inc., Macon, Ga. "Many moisture problems are caused by faulty flashing and windows, where water gets in behind the plywood or gypsum, causing rot, termite or other damage."

Grimes said there are many opportunities for water to get inside walls. He conducts moisture inspections for resale. homes, probing as many as 150 areas in a typical 2,500 sq. ft. home where moisture could possibly enter. "We probe around windows, doors, hose bibs, electric boxes, flashing, details, near headers and plate lines," he said. "I would say 70Vo to 807o of the damage we find is because of improperly caulked windows."

Housewrap can act as a secondary water resistant barrier by channeling incidental water via special surface grooves to the outside of the wall. Once installed between sheathing and insulating foam board, the product creates a drainage path for water or moisture vapor to escape.

As manufacturers work to create the perfect exterior wall system and builders and dealers look for ways to boost their margins, a quality housewrap offers an affordable and effective iolution. "The benefit to homebuyers is high while the cost to builders is relatively low, so dealers are selling more and more of this product," notes Weyerhaeuser's Schlehofer.