THERE'S SOMETHING BEAUTIFUL ABOUT INFRARED photography. That's especially true of infrared photos of older homes. From a heat-sensing perspective, the energy escaping from a 30-year-old home makes it light up like a cluster of stars in a dark sky. But as Joe Lstiburek, founder of Building Science Corp. in Waltham, Mass., points out, that metaphor is inaccurate. “An old house is not a battery,” he says. “It's a sieve. An energy sieve.”
But is that true of all homes, even those built in the last few months? To answer that question, Builder engaged Infrared Consulting Services, an infrared testing firm based in Minneapolis. We wanted to know whether the shell of a typical new home would visibly demonstrate better energy efficiency than an older one, due to better techniques, materials, and building codes.
We found that, indeed, newer homes live up to their superiority complex. Seen through an infrared lens, they show a narrower range of color differentials, which represents temperature. In the type of infrared images shown below, the “hot” spots show up yellow, while the coldest spots are black. The coldest temperature found in an image is typically listed in a black bar at the bottom of the color key.
In new homes, insulation is thicker and installed more consistently; window glazings are far superior to those in older homes and ductwork is generally tighter. As a result, the house generally performs better overall.
Old Habits On the other hand, even in the best insulated, carefully detailed new home, you're likely to see energy loss in the same specific areas found in a home built in 1960 or even 1980, although to a lesser degree. For example, every 2x4 stud in a conventionally framed wall shows up black in the infrared realm—a black, cold skeleton in every new home's closet. Scientists call these parts of the envelope “thermal shorts.”
A2x4 wood stud has a nominal R-value of only about 5, based on softwood's R-value of 1.25 per inch. That's less than half the R-value of the fiberglass batts surrounding it, at 3.33 per inch. Using conventional framing, even a well-insulated 2x6-framed wall with R-21 fiberglass bats, for example, has an effective R-value of about 12 to 17, according to research published in the newsletter, Energy Source Builder.
Take the typical 2x4-framed stick house. A study by Oak Ridge National Laboratory, in Oak Ridge, Tenn., found that the amount of wood framing in exterior walls accounts for 15 percent to 40 percent of the opaque area (without windows). Thus, the framing factor's impact on R-value is frequently underestimated because wall values are often based on center-of-wall measurements—where insulation fills the void—not wood.
That does not mean progress hasn't been made in making homes tighter. Back in the bad old days, before builders understood the importance of filling every void with fiberglass, energy loss was far greater than it is now. We also now aggressively seal sill plates, top plates, and other areas prone to high-energy loss. The reasons: Codes have become more explicit, and builders have become savvier—and more competitive.
Yet despite all of the advances in flashing, insulation, sill sealing, and other aspects of building science during the past 40 years, the envelopes of most conventionally built homes have come nowhere near their potential for energy retention.
Pushing The Envelope Why is that the case? Because even when a home is insulated perfectly, caulked, and sealed with care, the infrared eye can still find gaping holes in the energy “shield.” Where are these energy sinkholes? They're right in front of you. You know them better as windows, and, to a lesser degree, doors. That doesn't discount the fact that windows haven't seen tremendous energy gains. It's just that even the best window glazings still fall far short of the R-value of a well-built “opaque” wall.