Dow finds 'slow deterioration' in common building practice

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.”

Real-life lab

The TEETH houses were built by Cobblestone Homes of Saginaw, Mich., in late 2011 and 2012 to four different energy performance levels for Dow to study. They were all equipped with multiple sensors to monitor temperature, relative humidity and moisture content at several locations within the walls and above grade and below grade.

The six houses with the elevated moisture were built with 2-by-6 studs to meet International Energy Conservation Code (IECC) standards at the lowest possible price point. The 2006 IECC was used for the baseline performance and those houses came in at 77 on the lower-is-better Home Energy Rating System (HERS) index. The 2012 IECC standard was used for the next group of houses, which got a little more insulation in the basement and ceiling for a 59 HERS rating.

Dow also isolated the costs of the building materials related to energy performance and that came varied between $25,166 and $29,350 for the six houses.

Three other houses were built to 2012 IECC standards but with a focus on best practices rather than the lowest price point. Depending on the floor plan, the energy-related products cost as much as $33,902. Instead of R-19 fiberglass batt inside 2-by-6 studs, the builder used three inches of R-16 closed-cell spray polyurethane foam (SPF) in 2-by-4 studs. And, instead of OSB and a house wrap, an inch of Styrofoam structural insulated sheathing with a 5.5 R value was used on the exterior. Those houses rated a 54 on the HERS Index.

“Even though those walls are thinner, they are performing better from a moisture perspective as well as a thermal perspective,” Lieburn said. “You can see with an infrared camera that the continuous insulation is doing its job, preventing some of the heat loss from the inside to the out.”

Although the houses built with best practices cost about $5,000 more to construct, the initial expense will reduce the load on furnaces and air conditioners and save the owners money on years of utility bills.

“It will continue to pay dividends for the homeowner long after the house is constructed when you think about the cost of maintaining a comfortable environment,” said Linda Jeng, a chemical engineer at Dow.

The final four houses were built with 2-by-6 studs to exceed 2012 IECC standards. Their energy-related products, which included a more expensive furnace and windows, cost $40,644 to $43,194 and contributed to a rating of 48 on the HERS Index. Those houses also have two layers of foam on the exterior, 5 inches of closed-cell spray foam in the wall cavity, extruded polystyrene under the floor slab and thicker insulation than the other dwellings in basement walls and the ceiling.

“We wanted to find where the sweet spot is with performance and cost effectiveness,” Lieburn said. “We went beyond what anyone would expect to do with R-10 [insulation] on the outside in climate zone 5. The homes are performing with the least amount of energy but that is probably overkill in climate zone 5. You can dial that back.”

In the field

One of the goals of the study was to determine where the best value is created, in part to help builders make a strong case to homeowners about using high-performance materials to lower home ownership costs and even increase home resale values. The results of the Dow study show that by spending $5,000 more to build a house to 2012 IECC standards using best practices, they can bring the HERS Index rating down from 77 to 54.

However, many builders want to use OSB for shear strength as opposed to bracing the rigid foam walls with metal straps or strategically placed panels. In response, two years ago Dow introduced an over-sheathing guide at the International Builders Show to promote the advantages of using an inch of foam over OSB to the construction industry.

“Builders do care about energy but not tremendously because they're not paying the heating bills,” Lieburn said. “They're reluctant to spend more money if it could hurt their competitive edge and be harder to yield a return. However, they are interested in having a wall system that is durable, will reduce their call backs, and won't get them sued because of moisture problems. That's what we want to show builders with our TEETH project.”