Adding Insulation to Attic Floors

An extreme close-up of the end of a pink roll of fiberglass insulation.
What You'll Need
Utility knife
Duct tape

Adding insulation to attic floors is essential to keeping your home warm in the winter and cool in the summer. If installing insulation in this hard-to-reach space seems like a costly job or not worth the effort, consider how much money you will save. The high cost of heating and cooling is often due to the areas of the home that are not protected from external elements. Follow the instructions below to add insulation in these areas and, ultimately, save money.

Step 1—Install Vapor Barrier

Measure the attic floor to determine how much polyethylene you will need. Whatever the dimensions of the floor, you will need twice that amount of polyethylene sheeting.

If your house is unfinished, place the polyethylene on the ceiling below the attic floor, with its edges overlapping by 16 inches. Staple the material to the wood and duct tape it together. If the home is already finished, cut the polyethylene into strips that will fit between the unfinished floor spaces and then lay them inside and staple them in place.

Step 2—Select Insulation

The best insulation for attic floors is rolled fiberglass. Very rarely is there electrical or duct work inside the attic that will cause much of a problem when installing this type of insulation, and the process is easy.

Step 3—Determine Quantity of Insulation

Figure out how large of a roll of insulation you will need for the job. To do this, measure the floor joists. This will tell you if you need 23-inch or 15-inch wide rolls. Next, use an insulation calculator to figure out the square footage. With this information, choose the right amount of insulation. You will need polyethylene of the same amount.

Step 4—Install Insulation

Roll out the insulation along the floor and use the utility knife to cut it into strips that you can easily maneuver. You do not want pieces of insulation that will fit perfectly between the floor beams. They should be slightly larger than the space between the beams because you want them to fit snugly.

Once the insulation is cut, lay it down between the wood beams. Push it down so that it is even and flat against the polyethylene below. Continue cutting and placing until the entire attic floor is covered with insulation.

Step 5—Install More Vapor Barrier

Now that the insulation is in place, you can protect it more with another layer of polyethylene. Roll out the polyethylene and lay it over the attic floor. Trim as needed and, when you have to have multiple strips, overlap them by 16 inches and duct tape them down. You can then cover them with wood to finish the attic floor.