How to Install Unfaced Insulation

Insulating the walls and ceiling is an important part of any building or remodel job.

Unfaced insulation is sized to fit between standard-spaced wall studs.Unfaced insulation is sized to fit between standard-spaced wall studs.
Although there are several types of insulation available, one of the most common is fiberglass batt or roll. It comes compressed in plastic packaging and is precut to fit in the bay between standard-spaced studs. It comes with or without a facing of fire-resistant Kraft paper. The facing provides a moisture barrier and a way to secure the batts to the studs through stapling the paper. When there is no facing, simply stuff the batts in place, then provide a separate moisture barrier.

Consult with a local builder or use an online calculator to determine the R-value of the insulation you need. The Oak Ridge National Laboratory is one entity that provides such a calculator (see References).

Calculate the number of square feet of insulation you need. Simply measure the area of wall or ceiling space you have to cover and then multiply by a fraction to account for the studs. The fraction is 0.9 if the studs are 16 inches apart and 0.94 if 24 inches apart.

Open a package of unfaced insulation while wearing safety glasses and a dust mask. Cut the plastic with a utility knife. If you are using roll insulation, unroll it on the floor. If you are using batt insulation, remove a batt from the package.

Place one or two batts lengthwise in the bay between a pair of studs, then cut one more to fill the bay. If you are using roll insulation, measure the length of the bay and cut the insulation to fit first. Cut the insulation. Place a straight edge perpendicularly across the insulation, pushing down to compress, then cut along the edge with a utility knife.

Fill small spaces between pipes and in corners, cutting small pieces of insulation and stuffing them into the spaces.

Support the insulation, if you are placing it in the ceiling or between the floor joists under the house. Partially drive 1-inch galvanized nails in the joists or rafters on either side of a bay, weaving baling wire around the nails, then pound in the nails fully.

Staple a sheet of 4 or 6 mil polyethylene film to the joists, rafters or studs so it completely covers the insulation. The plastic film will form a moisture barrier that will protect the insulation from moisture-laden air inside your house. If you are laying insulation in the attic, spread the moisture barrier first, then lay the insulation on top.

Things You Will Need

  • Tape measure
  • Utility knife
  • Safety glasses
  • Dust mask
  • Straight edge
  • Hammer
  • 1-inch galvanized nails
  • Baling wire
  • 4 or 6 mil plastic sheeting
  • Staple gun


  • Most heat escapes through the ceiling. If you don't have sufficient insulation in the attic, you can add more by laying it on top of the existing insulation.


  • If you are laying insulation in the attic, keep it at least 3 inches away from any protruding light fixtures, fan motors and vents.

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.