Real Estate Trends: Moisture Management

At Urban NW Homes we get asked questions all the time about building homes in the rain and how builders prevent mold growth when everything gets wet. Since we have such a long rainy season here and so many homes to build, it’s not possible to wait for dry weather for roofing and framing. However, there are very specific strategies we use for building year-round in all weather.

First of all, it’s important to start with kiln dried lumber so that the wood is as dry as it can be. Then we frame as quickly as possible. For the roof, we use manufactured trusses to get the finished material on as quickly as we can. Next, we install a weather-resistant house wrap right away and begin the dry out process. The house wrap is made of weather-resistant material and goes around the walls and sills and door pans. The house wrap is vapor permeable so on the inside the wood is exposed, but the exterior can continue to dry through the house wrap. This allows the house to stay open and the wood can continue to breathe without moisture getting trapped. Then we get the windows on. At that point the home is completely waterproof. Water can’t get inside but any moisture on the inside can pass through the wrap. This way the drying process happens in both directions from the interior and exterior of the house. We wait at least a month before doing the siding because we believe it’s best to let the house dry as long as possible.

During the drying process we work on the inside of the house. Before installing interior drywall, we check the moisture content until it reaches a moisture level of 8 or 9 percent which is back to how we started with the kiln dried lumber. Another thing we do is leave the wall cavities open to continue drying. For example, if we’re putting in a fiber glass tub shower on the exterior wall, we install plywood sheeting behind the tub and shower and leave the wall cavity open to continue drying. A lot of builders will continue to install insulation and drywall which then locks in moisture with no way for it to come out, which turns into a breeding ground for mold. Another drying method we use is to place fans in the crawl spaces to create air movement for drying out. My superintendents are trained beyond the normal construction process to manage moisture and identify potential wet areas. If they notice a wet spot then they place fans strategically around the house to promote drying.

So basically, our approach to building through winter and the rainy seasons is to sequence the installation of all our products and give water an opportunity to get out if it accidentally gets inside. Wind-driven rain can be a challenge for building around here, especially when we build near the river or up in The Gorge. Urban NW Homes builds all over the county but also up north around Kalama and Woodland on hillsides which are exposed to all the rain and wind and weather that the Columbia River has to offer. We meet this challenge by continually checking for moisture content before installing insulation and again before drywall. We flash, counter flash, use penetration sealers, and inspect all exterior shell penetrations. We place just as much importance on side walls as a roof and are careful that things overlap correctly so moisture doesn’t get in behind something in the wrong sequence. Building through the rainy season isn’t a problem as long as you take extra measures to make sure the home dries out as you’re building.

Jerud Martin
Director of Construction/Owner
Urban NW Homes • urbannw.com  • 360-823-5480