Residential homes have gotten more efficient compared to commercial buildings since the 1990s, according to data from the Commercial Buildings Energy Consumption Survey, but Christine Williamson, president of Building Science Fight Club, warned that as homes have gotten larger, measuring efficiency by per square foot can be misleading.
However, she said, data on energy use by household and by individual residents supports the finding that homes are getting more efficient.
“Our homes have been getting so much more efficient that we’ve been able to compensate for having larger homes and fewer people living in each home, and that is really astounding,” she said during a webinar for Greenbuild Virtual International Conference and Expo.
The three most important factors contributing to a home’s energy efficiency are the glazing ratio, air tightness and insulation, Williamson said.
“These three factors are listed in order of importance,” she noted. “A lot of people, probably a lot of our clients, just sort of intuitively think that energy efficiency is mostly related to insulation.”
Glazing ratio is more important in commercial buildings, but in homes, where there are fewer windows than a big office building, air tightness is a huge opportunity for builders to construct comfortable, efficient homes for their clients.
Williamson pointed out that homes and offices are obviously built for different purposes. Residential design focuses on comfort, compared to productivity, which is the main function of a commercial building.
Comfort is hard to quantify, but is very noticeable to residents, Williamson said. Air tightness, in particular, is highly effective in making homes more comfortable for many reasons: dust and allergen control, pest control, odor control, acoustic performance, thermal regularity.
With that in mind, how can builders make homes more air tight and more comfortable for buyers?
Membranes. Fully adhered and fluid membranes are fully bonded to sheathing, creating a tighter seal, Williamson said. They’re more intuitive to use, and are available in different levels of permanence.
Some drawbacks include price, as well as temperature restrictions for when they can be applied. They may need primers or other special detailing to be applied correctly, she explained.
Integral sheathing works with water and air-control membranes that are applied to sheathing in a factory, then panel joints are sealed onsite, Williamson said.
Mechanically attached membranes are less realistic because they’re stapled to sheathing, which creates ways for air and water to get through, Williamson said.
Design. Builders need to look for areas where air can get through, and that tends to be big, obvious holes, not small, hard-to-see gaps.
“We can be shockingly bad at detailing large holes in our enclosure and really … pretty good at closing off the small ones, but not surprisingly, it’s the large holes that matter more,” Williamson said.
Attached garages, wall-to-foundation and wall-to-roof connections, ceilings, soffits and ducts are the biggest sources of air infiltration and exfiltration, she said.