Most homes in the U.S. have significant air leaks and not enough insulation. In fact, nine out of 10 of them are under-insulated, according to Energy Star. Those air leaksare expensive. Your home’s envelope ― the outer walls, windows, doors, and other openings ― wastes a lot of energy and increases your utility costs. On the other hand, a well-sealed envelope, plus the right amount of insulation, can save an average of 15% on heating and cooling costs (an average of 11% on total energy costs), the EPA reports.
Start in the attic, since that’s where you’ll find some of the biggest energy drains. Then tackle the basement to prevent cold air that enters there from being sucked into upstairs rooms. Finally, seal air leaks in the rest of the house. Here are eight places to start.
#1 Insulate Around Recessed Lights
Out of all the possible air leakage sites in a house, recessed lights, also called can lights, cause the worst leakage. The Pennsylvania Housing Research/Resource Center found this fact as part of an inspection protocol involving blower door testing and infrared imaging.
Lights labeled ICAT, for “insulation contact and air tight,” are already sealed; look for the label next to the bulb. If you don’t see it, assume yours leaks. An airtight baffle ($10 to $26) is a quick, 10-second fix. Remove the bulb, push the baffle up into the housing, then replace the bulb.
#2 Plug Open Stud Cavities
Most of your house probably has an inner skin of drywall or plaster between living space and unheated areas. But builders in the past often skipped this cover behind knee walls (partial-height walls where the roof angles down into the top floor), above dropped ceilings or soffits, and above angled ceilings over stairs.
Up in the attic, you may need to push insulation away to see if the stud cavities are open. If they are, seal them with unfaced fiberglass insulation (less than $1 a square foot) stuffed into plastic garbage bags; the bag is key to blocking airflow.
Close large gaps with scraps of drywall or pieces of reflective foil insulation (less than $2 a square foot). Once you’ve covered the openings, smooth the insulation back into place.
#3 Close Gaps Around Flues and Chimneys
Building codes require that wood framing be kept at least one inch from metal flues and two inches from brick chimneys. But that creates gaps where air can flow through.
Cover the gaps with aluminum flashing ($15) cut to fit and sealed into place with high-temperature silicone caulk ($10). To keep insulation away from the hot flue pipe, form a barrier by wrapping a cylinder of flashing around the flue, leaving a one-inch space in between. To maintain the spacing, cut and bend a series of inch-deep tabs in the cylinder’s top and bottom edges.
#4 Weatherstrip the Attic Access Door
A quarter-inch gap around pull-down attic stairs or an attic hatch lets through the same amount of air as a bedroom’s heating duct. Seal it by caulking between the stair frame and the rough opening, or by installing foam weatherstripping around the perimeter of the hatch opening. Or you can buy a pre-insulated hatch cover kit for stairs (about $60) or doors (about $373).
Related: How to Replace Weatherstripping
#5 Squirt Foam in Medium-Size Gaps
Once the biggest attic gaps are plugged, move on to the medium-size ones. Low-expansion polyurethane foam in a can is great for plugging openings that are a quarter inch to three inches wide, such as those around plumbing pipes and vents.
A standard 12-ounce can ($6) is good for 250 feet of bead about one-half-inch thick. The plastic straw applicator seals shut within two hours of the first use, so to get the most mileage out of a can, squirt a lubricant such as WD-40 onto a pipe cleaner and stuff that into the applicator tube between uses.
#6 Caulk Skinny Gaps
Caulk makes the best gap-filler for openings less than a quarter-inch wide, such as those cut around electrical boxes. Silicone costs the most ($10 a tube) but works better next to nonporous materials, such as metal flashing, or where there are temperature extremes, as in attics. Acrylic latex caulk ($4 a tube) is less messy to work with and cleans up with water.
#7 Plug Gaps in the Basement
Gaps low on a foundation wall matter if you’re trying to fix a wet basement, but only those above the outside soil level let air in. Seal those with the same materials you’d use in an attic: caulk for gaps up to a a quarter inch wide and spray foam for wider ones.
Use high-temperature caulk around vent pipes that get hot, such as those for the furnace or water heater. Shoot foam around wider holes for wires, pipes, and ducts that pass through basement walls to the outside.
In most older houses with basements, air seeps in where the house framing sits on the foundation. Spread a bead of caulk between the foundation and the sill plate (the wood immediately above the foundation), and along the top and bottom edges of the rim joist (the piece that sits atop the sill plate).
#8 Tighten Up Around Windows and Doors
In the main living areas of your home, the most significant drafts tend to occur around windows and doors. If you have old windows, caulking and adding new weatherstripping goes a long way toward tightening them up.
Bronze weatherstripping (about $25 for 17 feet) lasts for decades but is time-consuming to install, while some self-stick plastic types are easy to put on but don’t last very long.
Adhesive-backed EPDM rubber ($11 for 10 feet) is a good compromise, rated to last at least 10 years.
Nifty gadgets called pulley seals ($3.25 for a bag of 25 pairs) block air from streaming through the holes where cords disappear into the frames.
Weatherstripping also works wonders on doors. If a draft comes in at the bottom, install a new door sweep (about $12).
Before Working in the Attic, Take Some Precautions
Try to do attic work on a cool day. Wear protective gear: disposable clothes, gloves, and a double-elastic mask or half-face respirator. Bring along a droplight, plus at least two pieces of plywood big enough to span two or three joists to support you as you work. To save trips up and down a ladder, try to move up all of the materials you need before you get started.
One warning: If you find vermiculite insulation, hold off until you’ve had it checked for asbestos; your health department or air-quality agency can recommend a lab.