Part 2: Peering Through The Shell

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.

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.

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.

“Windows have seen a tenfold gain in efficiency in the last 10 years,” notes Lstiburek. “If only you saw the same gains in walls.” Most wall assemblies, he says, have changed little in that time—because there hasn't been enough demand from buyers and builders.

Along with better glazings, however, window usage has increased in new homes—reducing overall energy savings from use of better windows. Window walls have become a common design theme, and total window usage has grown from 8.6 units per home to more than 15 units per home since 1970, according to the National Association of Remodelers. Of course, home size during that period doubled as well, so the rise in number of windows has paralleled the “bigger is better” movement.

The Department of Energy has found that about 25 percent of a home's energy loss happens through its windows. That's because even the best triple-glazed, argon gas-filled window with low–solar-gain lowE glass has a U-value of only 0.14. U-value measures the number of BTUs that flow through 1 square foot of material in one hour. For comparison's sake, an R-15 (nominal) 2x4-framed wall has a U-value of about 0.081. This means that over the same period of time, the wall allows only half of the energy to flow through it as the glass.

So how can this gap in the building shell be improved? Insulated window coverings are one option, but these have never caught on in a big way. And it seems unlikely that home designers are likely to risk offering a plan with fewer windows.

Instead, reducing energy loss from windows has to be done more subtly. Lstiburek says that translates into using the best glazings available, reducing the number of north-facing units in northern climates (south, in warmer areas) and simply thinking more carefully about overhangs, siting, and the energy load required by each piece of glass.

Door manufacturers, on the other hand, have had more design flexibility than window makers in which to improve R-values. They, too, have made gains on the product's resistance to energy flow.

In the infrared view, you can see a huge difference between the solid wood door of yesteryear (about R-3) and the polyurethane foam–filled door of today (approaching R-10). The best insulated doors also include thermal breaks that enhance their efficiency.

At the same time, better caulking at the door threshold, sealing tape around the frame, and compressible weather stripping have made major improvements in the energy pedigree of the entire door assembly.

But to hear Lstiburek tell it, the real obstacle to taking homes to a higher level of energy efficiency—structures that don't glow under the infrared camera—is the human obstacle.

“We can save 30 percent of the total heating and cooling in a home right now,” he says, “just by shifting costs to other technologies. For example, you can use spectrally selective low-E glass, which costs 500 bucks more, and save that much on the HVAC. We can use 2x6 advanced framing [a framing method that reduces the amount of lumber used]. We can replace OSB and housewrap with insulating sheathing. But we won't. You know why? Because it requires change, and there's not enough pain to change.”

Lstiburek believes that rising energy costs—not necessarily the lack of energy resources (he believes we have enough fossil fuels to last 400 years)—will ultimately force a change on builders and buyers.

“There's only three ways to get builders to undertake the learning curve,” he says. “With fear, greed, or law. Fear is the fear of litigation. This has been the most successful technology transfer method in residential construction. Greed? Well, builders want to make more money, so as energy costs go up, they deliver a better house, which they build for the same cost and sell at a higher price. The other way, law, is by legislation, and I don't see that happening.”

Certainly not every builder needs a gun to his head before he starts building more efficient home envelopes. Many products already exist that push the building envelope to new heights of efficiency: insulated concrete forms, SIPs, straw bale, and Poly-Steel panels, to name but a few. Lstiburek doesn't argue that point. He just believes “we need a real mess” in terms of energy supply and pricing before most builders will take energy efficiency seriously.

“There's no question the products are getting better and better,” he says. “It's never been better in terms of new products or using technology. Everybody's gonna make out—the builder, the manufacturer, and the buyer.