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-vapour 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 fibreglass batts, cotton batts and spray foam. Fibreglass batts and cotton batts can be installed by do-it-yourself individuals, and spray foam needs to be installed by a licensed professional.
- Skill level:
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Things you need
- Tape measure
- Dust mask or respirator
- Long-sleeve shirt
- Long trousers
- 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, fibreglass insulation should be kraft-faced fibreglass batt insulation. "Kraft-faced" means that the fibreglass has a brown paper (kraft) on one side (face); the paper acts as a vapour 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 fibreglass 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 trousers 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 fibreglass. 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 vapour 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 and warnings
- Spray-foam insulation is about 40 per cent more effective than fibreglass or cotton batt insulation. The downside of spray-foam insulation is that it cannot be installed by as a doit yourself project and costs about 2 1/2 times the price of fibreglass or cotton batts.
- Information about spray foam and why it is used is on SprayFoam.com.