During an energy audit — or simply talking with an Arlington, TX air conditioning contractor — you will hear the word “envelope” quite a bit — building “envelope” and energy “envelope” are quite popular.

What the heck is a building envelope?

Or an energy envelope?

And why the word “envelope?”

In this post we define a home’s “envelope” — building, energy, whatever — and discuss why it’s important to the concept of a whole-house systems approach to energy efficiency.

The information is provided to give homeowners an understanding of heating, ventilation, and air conditioning (HVAC) terms and subjects when discussing repair, service, equipment upgrades, and energy efficiency with an Arlington, TX air conditioning contractor.

What is an “Building Envelope”?

This is not an in-depth definition of what constitutes a building envelope because, from a construction perspective, the answer can get quite detailed. For our simple purposes, a building envelope is the physical separators between the conditioned and unconditioned environment of a home, including resistance to air, water, heat, light, and noise transfer.

Our emphasis on the building envelope will be on how well conditioned air, cool or warm, is managed, which makes up the so-called Energy Envelope.

What is an “Energy Envelope?”

The “energy envelope” is how well the physical home . . .

• keeps cold air from leaking into the house during the winter, thus creating the need for the furnace to produce more warm air to keep the occupants warm (wasting energy and costing you more money each month)
• keeps hot air from leaking into the house during the summer, thus creating the need for the air conditioner to produce more cool air to keep everybody comfortable (wasting energy, placing additional strain on an already-taxed unit in the Texas heat, and costing you even more money)

Another way to look at it is a well-sealed home keeps the warm air inside and the cold air out in the winter and the cool air in and the hot air out during the summer.

You know the feeling: walk around the house and it feels “drafty,” like cold air is leaking in from a window or from under a door. These leaks are annoying but are not a major source of wasted energy.

The most significant air leaks are hidden in the attic and basement, which isn’t a problem in Arlington because basements here are rare. However, homes in general have plenty of sneaky places for air to leak.

The mission, if you choose to accept it, is to find these leaks and eliminate them.

Checking for Energy Leaks

Here are things you can check on a Saturday afternoon. Consider:

• Are the rooms drafty?
• Do you have unusually high heating and cooling bills?
• Do you have hot or cold ceilings in the house? Or entire rooms with hot or cold ceilings?
• Are there uneven temperatures between rooms?

Common Household Air Leaks

Your home is human-like. Like us, it “breathes” air in through leaks and “expels air” through the same leaks. It happens throughout the home — you’re just unaware of it.

Air leaks occur in:

• Dropped ceilings (images)
• Recessed lights (images)
• Open soffits (the box that frames recessed lights in the ceiling) (images)
• Attic entrances (images)
• Sill plates (images)
• Water and furnace flues (images)
• All ducts (including chaseways images)
• Door frames
• Chimney flashing (images)
• Window frames
• Outlets and switches (images)
• Plumbing and utility access (images)

Playing Sherlock Homes

Most air leaks you can investigate yourself, but if you feel the home is particularly “drafty” it’s best to call your Arlington, TX air conditioning contractor and energy efficiency specialist. But to get started, all it takes is to do a little sleuthing.

• Start by inspecting the attic for the air leaks mentioned above (here are some reference images) and check out the windows and doors.
• Perform a Light Test. Around windows and doors shine a flashlight at night over potential gaps while a partner observes from outside. Where you see light shining through that spot has an air leak. With lights on in the home, observe from the attic any light from the interior of the house shining through gaps and cracks into the attic.
• Perform a Smoke Test for Air Leakage (images). Turn on all fans and vents. Turn off all combustion appliances such as gas burning furnaces and water heaters on cool and windy days. Shut all windows, exterior doors, and fireplace flues. Turn on all exhaust fans that flow air outside. Light an incense stick or dust talcum powder (baby powder will do) into the air around the edges of common leak sites. If the smoke is sucked out of or blown into the room there’s a leak.

If you encounter any of the following you may want to call your Arlington, TX air conditioning service and repair contractor to make an assessment.

• If you find moldy or rotted attic rafters or floor joists (examples), there may be moisture problems, which require further investigation.
• If there’s wet or damp insulation (images) there may be a leak in the roof.
• If there are unsealed and uninsulated recessed “can” lights, special care must be taken when insulating around the fixtures.
• If kitchen, bathroom, and clothes dryer vents (images) exhaust moist air into the attic and not outdoors, that needs to be fixed.
• If the home has a history of ice dams (images) in the winter — usually not a problem in Arlington but they’re possible — and an indication of serious air leaks.

Tips for Sealing Air Leaks

A simple recommendation from Energy.gov is to create a room-by-room reference sketch to “get your bearings from below” and help locate areas where air leakage may occur.

Note soffits over kitchen cabinets and bath vanities, slanted ceilings, dropped-ceilings, where walls meet the ceiling, and recessed lighting. Use the sketch to guide you in the attic.

After a thorough inspection you will have a better idea where air leakage is occurring. Most of the materials needed to fix problems areas — like insulation, garbage bags, caulk, aluminum flashing, staples for the staple gun, and weatherstripping — can be purchased at an Arlington home improvement center.

• Plug the big holes first. Your biggest savings will come from fixing these. Use the sketch to locate areas where leakage is likely to occur. Look for dirty insulation, an indication that air is moving through it. Dropped soffits may be filled or covered with insulation, so push back the insulation or scoop it out to plug the holes, remembering to replace the insulation when finished.
• Create stuffed bags. Cut a 16-inch long piece of unfaced fiberglass batt insulation and carefully fold into the bottom of a 13-gallon plastic garbage bag. Handy to plug open stud cavities.
• Foam or caulk small gaps in the attic. Look for areas where the insulation is darkened, a result of filtering dusty air from the house. In cold weather you may also see frosty areas caused by warm, moist air condensing and then freezing as it hits the cold attic air. In warmer weather there will be water staining in the same areas. Seal the areas. It’s OK to re-use the dirty insulation.
• Don’t forget to seal the attic hatch or door. Use self-sticking weatherstripping. Treat the hatch like a door to the outside. Pre-made insulated attic door stair covers are also available from an Arlington home improvement center or on the web.

Special Challenges

The attic does offer some special challenges.

• Furnace flues require special sealing techniques. You’ll need to build at “metal dam” to keep the insulation away from pipes and heat sources.
• Recessed or “can” lights are a big source of air leaks and can make your home less energy efficient. These fixtures are like open holes into the attic. In the summer hot air makes the rooms warmer. In the winter can lights draw warm air up into the attic.

Homeowners can seal recessed lights themselves, but it can be difficult and requires patience and awareness to safety concerns. If you prefer not to mess with it, call a service or repair professional in Arlington or a local handyman.