How to Install Insulation

Determine the type of insulation needed for your attic:

• Batt and roll insulation (also called blanket insulation) are designed to fit between joists and wall stud cavities. Commonly used for DIY projects, they work well in open spaces like attic floors. We used batt insulation for our project.
• Loose fill insulation (also called blown-in insulation) is great for tight spaces and topping off existing insulation. You'll need a machine, which can typically be rented, when working with this material. For more information, see Install Blown-In Attic Insulation and our Insulation Buying Guide.

Determine the type of insulation needed for your attic:

• Batt and roll insulation (also called blanket insulation) are designed to fit between joists and wall stud cavities. Commonly used for DIY projects, they work well in open spaces like attic floors. We were installing batts insulation for our project.
• Loose fill insulation (also called blown-in insulation) is great for tight spaces and topping off existing insulation. You'll need a machine, which can typically be rented, when working with this material. For more information, see Install Blown-In Attic Insulation and our Insulation Buying Guide.

You should install two layers of insulation in your attic; wood joists must be covered to allow the air to move. The first layer will sit between the joists, and the second layer will run perpendicular over the joists. The first layer should have the facing against the drywall to act as a vapor barrier. (The general rule for insulation is that the facing always goes toward the conditioned space.) The second layer of insulation should be unfaced so that moisture doesn’t collect between the layers.

Determine how many square feet of insulation you’ll need by multiplying the attic's length times the width or using our Roll Insulation Calculator. When you purchase your insulation, keep in mind that rolls are good for long, continuous runs. Batts are best for small spaces.

Remove and replace any existing insulation that’s in bad shape, has been compressed or has mold on it. If you have a mold problem, fix it before installing the insulation. If you see signs of roof damage, call a professional.

Some houses have water pipes in the attic. Hot water running through a pipe in a cold attic space can cause condensation on the pipe, which will drip onto the insulation or attic framing. To remedy this and prevent moisture problems, wrap the plumbing with foam pipe sleeves. They just slide over the pipes, and you can cut them to length with a utility knife.

Make sure that all bath fans exhaust outside. If you allow a bath fan to vent into an attic, it'll lead to moisture problems. Some professionals recommend insulating vent ducts with HVAC insulation or using flexible insulated ducts. For more help, see Ventilate Your Home.

Seal air gaps to prevent heat loss around utilities and fixtures. Use spray foam in large gaps around pipes or light fixtures. Use caulk around smaller spaces like electrical boxes and other utilities.

Create barriers around heater flues to prevent a fire hazard. Run a bead of high-temperature caulk around the flue and then press two pieces of sheet metal into the caulk to surround the flue. Staple them to the joists.

Check any recessed lights to see if they’re rated Type-IC, which means they’re acceptable for insulation contact. The label might be inside the housing. If the lights aren't rated Type-IC, you’ll need to keep the insulation away from the fixture to prevent a fire hazard.

If needed, build a box with drywall and screws to create a 3-inch space around the fixture. The drywall facing should be on the interior side of the box. Then apply spray foam along the seams and where the box meets the ceiling.

Insulate skylight passages. Drywall shafts can allow heat to escape. There are several ways to insulate skylight passages. One method is to fill the gaps between the studs with faced batts and then wrap the entire passage with unfaced insulation. The unfaced insulation can be secured to the framing with staples.

After securing the insulation, wrap the entire passage with house wrap and seal the seams with house wrap tape. The house wrap helps hold the insulation in place and slows airflow.

Check the airflow in your attic. Even though you want to prevent heat loss through your attic floor, air must flow to prevent moisture buildup. The air enters through the soffit vents near the attic floor, travels up toward the ridge vent and exits through the attic. To allow this airflow, install rafter vents at the soffits. Just slide them along the underside of the roof to the soffit and attach them with staples. The batt insulation will sit against the vents. For more help, see Install a Ridge Vent.

If you intend to use your attic for storage, you’ll need to build a storage deck (if not, skip to Step 14). Remember, there will be two layers of insulation, so the deck will need to be above the height of the second layer. To create a storage deck, build a framework of 2-foot-by-6-foot boards running perpendicular over the existing joists. Secure everything with screws or nails. You can build the deck any size you want.

Install insulation between the joists and then secure plywood to the top of the framework with screws.

If your house doesn’t already have a layer of insulation between the joists, you’ll need to install one before adding a layer over the joists. Start in a corner away from the attic hatch and fit the roll insulation between the joists, facing against the drywall. Make sure it’s tucked into the tight spaces where the rafters meet the ceiling joists. As you’re working, be careful not to compress the rolls; fiberglass becomes less effective when it’s compressed. Use a straight edge and utility knife to cut the rolls as needed.

There are several ways to insulate a stair hatch. One method is to apply self-adhesive weatherstripping where the door makes contact with the framing.

Apply adhesive to the back of the hatch and press a piece of rigid foam onto the adhesive. Use cap nails if needed to hold it in place.

Now that your attic is properly insulated, you can enjoy a cozier and more energy-efficient home.

When insulating floor joists, start at one edge of the crawlspace and install the insulation between the floor joists. If using faced insulation, keep the paper vapor retarder facing up and against the subfloor. The insulation should fit snugly against the subfloor and between the joists. Make sure each run contacts the insulation you installed at the header/band joists.

Cut the insulation as needed to fit any narrow spaces between floor joists.