How to Install Blanket Flat Roof Insulation

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  • 4-12 hours
  • Beginner
  • 150-500
What You'll Need
Blanket insulation
Utility knife
Straight edge
Tape measure
Staple gun
Plastic sheeting

Installing blanket flat roof insulation can be done by even a novice do-it-yourselfer. If you have an exposed ceiling below a flat roof, consider installing blanket or batt insulation. This insulation is made of fiberglass and will provide a barrier between the inside of the house and the roof. It will decrease the heat transfer that you experience and make it more comfortable, not to mention decrease your energy bills.

Step 1 - Take Accurate Measurements

In order to cut the insulation to size, you will need to take accurate measurements. Use your tape measure to measure the length of the channels between the ceiling framing members. Write down the length of the channels. It is important.

Step 2 - Cut the Insulation to Length

Now that you know the proper length, you can cut the insulation. An easy way to cut it is to place a straight edge on the top and cut through the insulation with your utility knife.

When working with fiberglass insulation, you should wear gloves and a long sleeve shirt. If the fiberglass touches your skin it can cause irritation.

Step 3 - Press Insulation in Place

Depending on the height of your ceiling, you may need to use a step ladder to place the insulation. Put the long runs in place first. Then, use the remnants to fill in the smaller spaces. Place the insulation between the joists with a bit of pressure.

You should definitely check the local building code to make sure you don’t have to leave any air space. Building codes change all the time and you want to make sure that your insulation job meets code.

Step 4 - Staple Paper Flange

While holding the insulation in place with one hand, staple the overhanging paper flange to the joist, stapling every six inches to create a tight fit. Repeat this process until the entire ceiling below your flat roof is covered and stapled.

Step 5 - Apply Plastic Sheeting

If you are planning to add a drywall ceiling after you install the installation, you will want to make sure that the facing on the insulation will actually butt up against the dry wall. You would begin to hang the drywall ceiling at this point.

If you are going to leave the ceiling exposed, you should apply heavy-duty plastic sheeting. Begin in one of the corners and staple the plastic over the insulation as you go. Staple it to the joists and along the top. The plastic should be pulled taut. That way, it is easier to work from joist to joist. This also makes it easy to overlap the plastic. Overlap the plastic as far as one complete cavity.

That’s it. You have insulated your flat roof with blanket insulation. You should now experience less extreme temperatures and a decrease in your heating and cooling bills.