A five-year study of 12 research homes designed to help builders and buyers select the best materials is winding down in Midland, Mich., and scientists with Dow Building Solutions say one of their findings raises questions about a common method of construction.
For four winters, Dow scientists measured elevated moisture in six of the dwellings in the unique neighborhood dubbed Twelve Energy Efficient Test Homes (TEETH). Those houses were built with 2-by-6 wood studs, oriented strand board (OSB), R-19 fiberglass batt insulation and a house wrap on the outside.
That's been a popular way to frame a dwelling since the late 1970s. However, the TEETH tests have revealed something new about the conventional wisdom that says the moisture dries to the outside of houses built with that insulation strategy, according to Brian Lieburn, a Dow research scientist.
“Every winter, even the mild winters, we're getting wet walls in that strategy,” Lieburn said. “People are accustomed to believing that it breathes and dries to the outside. It does dry to the outside — the following spring. But from December through April we're measuring moisture.”
Too much moisture in a house can cause problems, such as mold and mildew, which can trigger allergic reactions. It can also cause structural wood to rot, drywall to swell, and hamper the performance of insulation, which could lead to higher heating and cooling bills.
Dow building experts brought in colleagues from Dow Microbial Solutions to determine if four winters of elevated moisture had taken any structural toll on the six houses.
“We wanted to do some forensic work on that,” Lieburn said. “So we got into the walls. We took siding, house wrap and OSB off and we looked for evidence of decaying OSB, water staining and other things.”
The TEETH researchers saw water staining at the plate of some of the six houses as well as rusting on some fasteners but very little active mold growth except for one area, Lieburn said. Microbial swabs and OSB samples then were sent to a lab and examined under microscopes and subjected to bending tests to determine if there was any deterioration or loss of strength.
The lab tests indicate that the moisture in the walls is causing damage but at very slow rate.
“We know it's getting wet and we know when it gets wet it is also cold so it is in a refrigerated state. That's what is helping delay the growth of fungi and decay,” Lieburn said. “Houses all over the United States are built like this. This is happening in a lot of them. They're just not decaying rapidly. There's a slow deterioration.”