Improving Efficiency With a Tighter Building Envelope

You’ve switched the light bulbs from incandescent to compact fluorescent, upgraded appliances to Energy Star models and set up a regular furnace-filter replacement schedule, but your energy costs are still rising. If this scenario sounds familiar, it may be time to look at more extensive efficiency-boosting improvements.

A good first step to better energy performance is to take a closer look at the walls, doors and windows that separate your interior spaces from the great outdoors. These elements, collectively called the building “envelope,” are the critical components protecting occupants from winter’s winds and summer’s heat. Making the envelope as airtight as possible can result in significant reduction in heating and cooling needs.

Sealing the gaps
The most efficient building envelope would be a continuous surface with no breaks or changes in material. Of course, we’d never be able to enter or exit such a structure, so its usefulness would be pretty limited. Instead, efficiency-minded property owners and managers should focus on sealing around any penetrations in the envelope.

Andy Bush of Columbus, Ohio-based remodeler Michael Matrka, Inc. where he is in charge of small projects and services, outlines a number of potential leak areas in the building envelope, including:

• Windows and doors
• Fireplaces
• Attic access hatches
• Penetrations such as electrical, plumbing and air-exhaust vents

Points where there is a transition in building materials are another area where energy can be lost. Because materials expand and contract differently, cracks can open up over time at those points where they come together.

“It’s very common for air to infiltrate where the treated plate meets the basement foundation,” Bush says, citing one such example. “Even a good sill seal doesn’t do the job right.”

Closing the window on efficiency losses
Windows are probably a building’s biggest potential energy sieves, and an investment in high-efficiency, double-pane models can pay for itself quickly. But if you don’t have the upfront cash for such an expense, there still is room for improving the performance of existing units. Just upgrading the seals around these openings can help cut air-infiltration rates.

“A lot of windows were installed incorrectly, and we didn’t have the flexible flashing tapes we have now,” says Ren Anderson, manager of residential research at the National Renewable Energy Laboratory in Golden, Colo., and technical leader for the U.S. Department of Energy’s Building America program. “To get at those points, you have to pull the trim off the windows from the outside to get at those gaps and seal them up.”

However, Anderson says, be sure not to caulk along the bottom of the window, or you may end up trapping water inside the building cavity. If drain holes are blocked, moisture can build up, creating conditions that could promote damaging mold and mildew behind your buildings’ walls.

Where to start
Several tests can help you determine where a building’s envelope is less than secure. The easiest is to simply run your hand around window and door frames during a windy day to see if you can feel air passing through. Similarly, curtains, shades or blinds that move when the wind blows outside are key indicators that windows could use sealing. And, obviously, if you can see daylight around window, door or chimney trim, it’s time to get out the caulking gun.

More sophisticated testing is available from insulation installers, or your utility company may be able to point you toward local energy-audit specialists. These pros can use thermal-imaging cameras to detect leaks, or building walls lacking adequate insulation, Bush says. They also may run a “blower door” test, in which all windows—and all but one door—are sealed, and a large fan is installed in the last unsealed door. By setting that fan to exhaust and establishing a negative pressure inside the building, the test can help establish where air is penetrating the building’s exterior walls.