That’s a Wrap

He adds: “We promote a drainage system as opposed to a barrier system where you just try to block the water. With the drainage system, if water does get behind the window or door, there is a way for it to get back out.”

Downside of Tight Homes

The downside is that by reducing energy and air coming across a wall system, you reduce the amount of energy available to help dry the home. “What you’re trying to do is reduce the outside energy coming in or the inside energy going out, so there’s less energy available to help dry the wall system. That means you better get your wall system and your water-management system done right. In tighter homes, water management takes on even greater importance,” Hubbell says.

Making homes more efficient and comfortable is not just a simple matter of saying “let’s put more insulation in and seal everything up tighter than ever,” Hubbell notes, adding, “exterior insulation or leveling board may create problems because they’re relatively impermeable and act like an unintended vapor barrier. That’s why it’s so important to understand the building science behind the wall system and how things really work.”

There are three main problem areas where moisture in the form of water can get into buildings, according to Easley:

• Roof and wall intersections
• Around doors and windows
• Other penetrations, such as dryer vents

Like Hubbell, Easley sees the importance of permeability and the ability of the housewrap to let materials dry. “Drying is the real issue because it only takes seconds for building materials to get wet, but it can take days or weeks for hygroscopic building materials, like framing and OSB sheathing, to dry out. Once the water gets in, you want to dry out the wall system as quickly as possible,” Easley says.

Job One

Deflecting water is job one, according to Easley. Avoid situations that trap water, such as valleys that confine water and bring it into the building envelope. One such situation is a 1-story roof meeting a 2-story wall. “Water that runs off a 2,000-square-foot roof in 1-inch rainfall can easily deposit 1,200 gallons of water, so if you don’t deflect that water away it can easily be guided into the building envelope,” he says. “At roof-wall intersections it’s essential to use a good-quality seamless kick-out flashing.”

Job two is if water does get into the wall system, drain it as quickly as possible. “The faster you can drain the water away, the less it gets absorbed into hygroscopic building materials,” Easley says. Some manufacturers have come up with “drainwraps” that have a surface with deposits of plastic or other means of creating a texture so there is a drainage space between the wrap and the smooth undersurface of the cladding product.

Job three must take place when building materials get wet: Dry them as quickly as possible. “These are the three things you need to do, and tying it all together is really important. You have to think of it as a system,” Easley says.

Improper installation can cause many problems, as Hubbell points out. Easley agrees: “When contractors install windows, they’ll just put flashing around the building wrap to the window, but what you need to do at the top of the windows is cut the housewrap and fold it; then put the head flashing from the nail fin of the window up onto sheathing, so if water gets behind the building wrap, it runs down and hits that head flashing and runs to daylight. It doesn’t get between the window and the framing and into the house.”

The standard remodelers should follow is ASTM E2112 (see “Three Steps to Integrating Replacement Windows and Doors into the Building Envelope,” page 78), Easley recommends. “That’s the national window flashing standard upon which most window manufacturers base their installation instructions. Housewrap manufacturers also cite ASTM E2112.”

Misused Terms

Easley, too, encounters confusion about the terms surrounding housewraps, weather-resistant barriers and similar labels. “Often people misuse the term vapor barrier when they really mean weather-resistant barrier. The way the IRC explains these materials is that a vapor retarder is typically put on the warm side of the insulation,” he says.