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What Is the Correct Way to Install Insulation?

Insulation makes a home more energy-efficient, and works best when installed correctly. No matter which type you install, it won't be effective if you leave gaps through which air can pass. Moreover, loose insulation such as fiberglass batts and blown-in cellulose require a vapor barrier to prevent clumping and gaps. Although most insulating materials are treated with a fire retardant, they can still burn if they are installed too close to a source of heat. While you should avoid gaps, you should nevertheless allow for venting when insulating the attic.

To get the best insulation R-value, there shouldn't be gaps.

Install faced fiberglass insulation with the paper backing facing toward the room. The backing is made of kraft paper that resists moisture and provides a vapor barrier to protect the insulation from condensation from the heated room. Place the insulation in the bay between a pair of studs and staple it to the stud faces with a staple gun.

Stuff unfaced fiberglass batt or roll insulation into the bay between studs, then cover it with a 4- to 8-mil plastic sheet and staple the plastic to the studs. The plastic will provide a vapor barrier.

Place faced and unfaced batts in a wall or ceiling bay so the ends are touching, but not compressing against each other. Don't compress batt insulation to fit in a small space. Cut the batts to fit with a utility knife.

Lay the vapor barrier first when insulating an attic space. Either lay a sheet of plastic in each bay or install faced insulation with the backing facing down. Leave the top of the insulation uncovered so it can breathe.

Stuff small pieces of fiberglass batt insulation into gaps around electrical boxes, between pipes and wires and in corners without compressing them. Leave a 3-inch gap between the insulation and any fixture that generates heat, such as a wall heater or light fixture. Stuff insulation into the gaps between doors and windows and the framing or, for more effective insulation, spray foam from a can into the gaps. Let the foam harden, then cut it flush to the studs with a utility knife.

Staple a sheet of plastic to an unfinished wall before you install loose-fill cellulose or fiberglass insulation. The plastic will give vapor protection and will also hold the insulation in place until you cover the wall. Install the insulation by pouring it behind the plastic from the bag, dropping it in place by hand, or blowing it with an insulation blower.

Leave soffit and other air circulation vents clear when you are installing any kind of insulation in the attic. Covering them will promote the growth of mold and rot.

Spray foam insulation with an insulation sprayer, then cut it flush to the studs with a reciprocating saw when it dries. Spray insulation can be hard to work with and applying it is best left to a professional. If you do it yourself, wear protective clothing, eye protection and a respirator.

Things You Will Need

  • Fiberglass batt insulation
  • Staple gun
  • 4- or 8-mil plastic sheeting
  • Utility knife
  • Canned spray foam insulation
  • Loose fill insulation
  • Insulation blower
  • Spray foam insulation
  • Foam sprayer
  • Reciprocating saw
  • Protective clothing
  • Safety glasses
  • Respirator

Tip

  • If your walls are already covered, the best way to insulate them is with blown-in loose fill. Since you can't install a vapor barrier, however, it may clump over time. It is also an attractive nesting place for rodents.

Warning

  • Wear protective clothing and a respirator when installing any kind of insulation, especially fiberglass, which is a skin and lung irritant.

About the Author

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.

Photo Credits

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