How To Insulate an Attic for Lower Energy Bills

by Benjamin Roussey
How to Insulate Attic photo

Want to keep your home warmer in the winter and cooler in the summer for less? Take these steps to make sure your attic has enough insulation to keep energy bills in check.

Insulating the attic is one of the most effective ways to keep your home warm during the winter months and cooler in the summer. You will not only make your home more comfortable, but you will also be saving a lot on energy bills. Here are some important tips to help you effectively insulate your attic.

Selecting the Right Insulating Material

Insulating materials have an R-value, which is the material’s resistance to heat flow. The insulation is more effective with a higher R-value. Secondly, insulation materials have a cumulative effect on the R-value. For instance, if you install two layers of R-15 insulating material, the total value of insulation will be R-30.

There are two typical types of insulation for an attic: blanket insulation and loose-fill insulation.

Blanket insulation comes in rolls, and the material is comprised of fiberglass and a combination of the other fibers such as cotton, mineral wool, and plastic. Blanket insulation is available in different lengths and widths, making installation quite easy. On the other hand, loose-fill insulation can be installed only with special equipment handled by professionals. This insulation, comprised of clumps of materials like mineral wool, cellulose and fiberglass, is sprayed into the cavities of the attic wall and floor. It is also more expensive.

The recommended insulating R-value for Northeast, Northwest, Southwest, and Midwest of United States is R-49. For the California, Florida, Hawaii, Texas, and Louisiana coastlines the recommended R-value is R-38.

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Before installing insulation, prepare your attic to make your work easier and safer. If there are no lights, then first you should install some temporary lighting. Then lay boards wherever required across joists to make walkways and hold the materials and tools.

Sealing Air Leaks

Before proceeding with installation of insulation, it is very important to seal all the air leaks in your attic. The usual areas where air leaks are possible include attic access panels, pull-down stairs, exhaust fan housing, recessed lighting, plumbing stacks, chimneys, and around interior partitions.

Use rigid boards for insulating access panels, and for the attic door, add a door sweep and weather strip. For pull-down stairs, use an airtight cover with insulation. Insulating around recessed lights can be tricky, as you need to keep the insulation away by three inches to avoid fire hazard. However, fixtures with IC (Insulation Contact) rating do not have this drawback.

It is best to replace recessed lights with ceiling mounted or airtight fixtures. The collar around metal chimneys is usually loose and has to be repaired with a fire-rated sealant. For gaps on the top of interior walls, use caulk, and for plumbing stack vents, use expanding foam sealant.


Ventilation in the attic is as important as sealing air leaks.

When installing insulation, make sure the ventilation is not blocked off. Ventilation should be planned to balance the exhaust and intake openings.

About 50% of the venting should be used for drawing in air through soffits. It is better to have ventilation chutes, since they allow proper insulation to be installed at the edges.

Proper ventilation in the attic will help prevent moisture build-up. If there is buildup of moisture, it will not only ruin the insulation but also cause various health issues in the home. Plus, outstanding ventilation will prevent the formation of ice dams. These formations can drive water below the shingles, which will damage walls and the roof.

Checking for Water Leaks

Insulation can become quite ineffective when it is wet. Therefore, it is very important to check the attic ceiling for water leaks. Look for water stains or marks, and make the necessary repairs to stop the leak.

Installing Insulation

Blanket insulation is ideally suited for attics without floors, and you could lay the insulation rolls between joists. Look for rolls in exact lengths to cover the space, and try to avoid cutting the material. When laying rolls adjacent to each other, you should butt them tightly together. A gap of even an inch can reduce the R-value by 25%. If there is wiring, slide the insulation underneath the wires without disturbing any connections. Make sure the insulation is a snug fit around the cross braces, and you can cut the material to have a tight fit. If you are installing double-layered insulation, then the second layer should be laid perpendicular to the layer underneath.

For attics with floors, loose-fill insulation can be used for insulating the area beneath the floor. Additional insulation of either loose fill or blanket insulation can be added over the floor.

Insulating an Attic Ceiling

Try to get the roll length that will fit inside the joist width. Blanket insulation is usually available in standardized widths of joists. If your joist placement is irregular, then you will have to cut the roll to size. Place the blanket insulation against the ceiling and make sure the paper barrier for vapor is facing the attic space. If the insulation has side paper flaps, then staple these flaps to the edge of the studs.

Do not flatten the insulation while installing, since that will reduce the insulating effect. If the roll does not come with a paper vapor barrier, you will need plastic sheeting to serve that purpose and hold the insulation in place. When you are installing ceiling insulation, avoid covering exposed wiring, electrical outlets, or light fixtures, since that would create a fire hazard.

Reviewed October 2022

About the Author

Benjamin Roussey is from Sacramento, CA, and grew up doing all varieties of home improvement projects around the home since his parents did not hire contractors or outside help to maintain their home or vehicles. As a result, he has acquired a multitude of home handyman skills in plumbing, carpentry, electrical and everything in between. He also has two Masters degrees and he served four years in the U.S. Navy.

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