Rainscreens Mean Smart Building Science

The root of the problem when it comes to moisture damage in homes – even multi-million-dollar homes, is the ignorance, willful or otherwise, of proper building science. Though building practices have improved, there is a glut of existing homes that were built improperly.
"The root of the problem is often the technology and products being used a decade ago," explains Lee Haller, owner of Haller Custom Homes, a builder of high-end homes and residential neighborhoods in the western Philadelphia suburbs. “Today, building science experts have found that some building products and faulty installation methods used just a short time ago have contributed to the structural damage that homes are currently experiencing today.” 

Haller Custom Homes specializes in remediating moisture damage such as this window in suburban Philadelphia h

Haller says the construction industry has taken great strides to create new approaches to avoid bulk water intrusion, and to drain and dry any water that does manage to penetrate the exterior cladding. But what to do with newer homes that were built before these best practices were introduced? 
Haller’s company specializes in remediation and restoration of moisture-damaged homes near the Philadelphia Main Line. “(People) were experiencing the same type of problems with bulk water intrusion, which can lead to mold growth. Communities that were built at the same time – using the same contractors, building practices, and materials – often share the same problems,” says Haller. 
One solution to avoiding the problem of bulk water intrusion has been the incorporation of a rainscreen system in the home’s design. A rainscreen, as described by the National Association of Home Builders (NAHB) Research Center, is a moisture-management system incorporating cladding, an air cavity and a drainage plane to shed moisture and prevent moisture intrusion and the resulting premature decay in homes. 
Haller adds that builders constructing homes without a rainscreen system behind any absorptive cladding like stucco, stone or fiber cement should also think twice. “I know for a fact that the builders who are dealing with liability issues for the repair of the original construction are finding that the cost of the repairs totally erase the profit they made on the home when it was first built, and then some,” he says. “I say spend the little bit extra when the home is being built and avoid the huge possible expense down the road.”
The NAHB recently issued an educational guide that discussed the need for better drainage behind so-called “absorptive” exterior claddings, which include any materials that are semi-porous and may transmit or retain some water. This can include stucco, manufactured stone, stone veneer and even fiber-cement siding. Among the products referenced that can be used as part of an effective building envelope system is a wall drainage spacer, described as an “open-weave plastic mat.”

Haller uses Benjamin Obdyke’s Home Slicker Stone & Stucco, shown.

Haller’s Approach:

• After studying the home’s condition, erect scaffolding and begin removing the stucco. 
• Examine the sheathing. If the OSB or plywood is damaged, replace it. With OSB , run a circular saw around the joints of the OSB to create a 1/16-inch gap. 
• Replace damaged 2 x 4s or other structural framing. 
• If windows are damaged or other specific conditions are present, re-install them or replace them using the latest wrap products and flashing for moisture-resistance. Cover the windows for protection. 
• Remove the cornice and apply the water-resistant barrier to the entire wall, including behind where the cornice had been. Gables are extended to create an overhang to prevent water entry. 
• Install Benjamin Obdyke's Home Slicker Stone & Stucco. 
• House is watertight at that point and ready to stucco.

The product’s vertically channeled matrix forms an air space for drainage and drying, while a breathable fabric attached to the product blocks mortar from clogging the newly formed cavity. It creates a pressure-equalized air space and capillary break immediately behind exterior cladding to speed the drying of moisture that accumulates in the wall assembly by providing a drainage space and allowing air to move in a convective fashion throughout the wall cavity.

Alternatives to Home Slicker include offerings from:

• Sto Corp
• Vaproshield
• Dow
• Masonry Innovations