How to Install Basement Insulation in the Ceiling

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Fiberglass insulation and a few of the tools are required for installation.
Fiberglass insulation and a few of the tools are required for installation. (Image: Comstock/Comstock/Getty Images)

The first item to consider when insulating a basement ceiling is the basement floor. If the floor is concrete, then just about any type of insulation can be installed in the ceiling. If the floor is soil or soil with a poly-vapor barrier, however, pay close attention to the type of materials you use for insulation. The second factor to consider is the type of insulation. Choices are fiberglass batts, cotton batts and spray foam. Fiberglass batts and cotton batts can be installed by do-it-yourself individuals, and spray foam needs to be installed by a licensed professional.

Things You'll Need

  • Tape measure
  • Dust mask or respirator
  • Long-sleeve shirt
  • Long pants
  • Gloves
  • Straight edge
  • Utility knife
  • Step stool or ladder
  • Staple gun
  • Metal insulation supports

Determine the type of insulation you want to use. In most basement applications, fiberglass insulation should be kraft-faced fiberglass batt insulation. "Kraft-faced" means that the fiberglass has a brown paper (kraft) on one side (face); the paper acts as a vapor barrier. Cotton batts can be used in dry basement applications only when the floor is concrete and no water issues exist. Spray foam can be used in all basement applications, but, as previously mentioned, it must be installed by a certified spray foam company.

Determine the size of insulation required. Both fiberglass and cotton batts are in specific depths or thicknesses. Use R-19 or 5-inch thick insulation for a 2-by-6-inch joist. Use high-density R-30 or 8-inch thick insulation for a 2-by-8-inch joist, R-30 or 10-inch thick insulation for a 2-by-10-inch joist and R-38 or 12-inch-thick insulation for joists larger than 10 inches.

"R" is the insulation industry standard value of the insulation's thermal resistance. Higher numbers designate better thermal performance.

Measure the square footage of insulation required, and multiply the result by 0.9 in order to purchase the correct amount of insulation. Multiplying by 0.9 removes the widths of joists so you don't end up with several extra bags of insulation at the end of the project.

Wear a dust mask or respirator along with a long-sleeve shirt, long pants and gloves to cut down on the insulation material's contact with your skin, which may cause itching.

Cut the insulation to length by first rolling out the batt insulation with the paper side on the ground and pressing the insulation down with a straight edge, such as piece of 2-by-4 or a level, to help compress the fiberglass. Cut the batts with a utility knife along the straight edge.

Install the batts with paper side touching the subfloor of the first floor. It is very important that the paper side faces up, toward the living space, to ensure that the vapor barrier (the kraft paper) touches the warm side of the house.

Simply push the insulation into place between the ceiling joists, and staple the paper to the underside of the subfloor with a staple gun. Also install metal insulation supports every 16 inches by simply pushing them into place.

Tips & Warnings

  • Spray-foam insulation is about 40 percent more effective than fiberglass or cotton batt insulation. The downside of spray-foam insulation is that it cannot be installed by as a do-it yourself project and costs about 2 1/2 times the price of fiberglass or cotton batts.
  • Information about spray foam and why it is used is on SprayFoam.com.
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