How to Insulate Roof Rafters

If you have uninsulated roof rafters in your attic, they are costing you money in energy bills every second the heat is on. Attics, especially in old homes, are rarely insulated, leaving no separation between the outside elements and the attic other than a piece of plywood and maybe some shingles. This is not an ideal situation to prevent heat loss and save money as heat will escape the attic. Properly insulating roof rafters is not a difficult thing to do and it is not even expensive. There are many insulation options for properly insulating roof rafters. Follow these steps to learn how to properly install insulation to your attic roof rafters.

Step 1 - Measure the Space

Climb into the attic and use the measuring tape to determine the square footage of the space. You do this by multiplying the length and the width of the attic. You do not need to be too precise with your measurements. Use this square footage to purchase the right amount of insulation and plastic sheeting.

Step 2 - Cutting and Fitting the Insulation

If you're using blown insulation around your roof rafters, you can skip this step. Measure the distance between the roof rafters in the attic and cut the rolled insulation to these measurements. It is better to have insulation that is cut wider and slightly longer than it is to have them smaller. Roll out the plastic sheeting over the attic floor as well and trim it so that there is enough to climb up the walls by several inches. If you have multiple pieces of plastic, that is perfectly fine.

Step 3 - Installing the Insulation

If you are using blown insulation you should follow the instructions on the bag. It is common for different blown insulation to have different instructions associated with it. Typically, you will fill the insulation blower with the insulation and blow it between the attic floor joists and then blow another layer on top of the roof rafters. If you have a solid floor covering the roof rafters, use the claw end of the hammer to pull it up in several locations and blow the insulation under the boards. Replace the floor board and then spray more insulation on top of it.

Using rolled insulation is a more detailed process. Place the cut insulation between roof rafters and make sure it is flush against the wood. An inch gap can cause 20 percent heat loss. Feed the rolled insulation under wires and pipe if either is present. Place the plastic sheeting on top of the rolled insulation. If the plastic sheeting is in pieces, overlap the pieces by 8 inches and staple in place directly to the roof rafters and the wall. If there is a floor, you will need to remove it to properly insulate the roof rafters. If this is your situation, do not use plastic sheeting.