How do I Insulate an Attic?

J.M. Densing

Installing insulation in an attic is a good way to reduce energy consumption and costs. If your attic is unfinished, you should insulate the floor; if finished, do the walls and ceiling. The two main types of insulation are roll or blown insulation. The first step to insulate an attic is to select the insulation and calculate the amount needed by following recommendations for the climate where you live. Next, prepare the attic, including sealing air leaks such as the area near the attic stairs. Then carefully follow the installation instructions and complete the process.

Batt insulation is sometimes used in attics.
Batt insulation is sometimes used in attics.

An uninsulated attic can be a major waste of energy, thus allowing heat to escape in the winter and air conditioning to escape in the summer. If you have an unfinished attic, the insulation should be installed on the floor between the joists to prevent heat transfer between the attic and the rest of the house. If a finished attic, currently or in the future, insulate the walls and ceiling to prevent heat transfer with the outdoors and keep the space comfortable.

Almost half of the heat lost in homes is lost through the ceiling.
Almost half of the heat lost in homes is lost through the ceiling.

The main types of material to insulate an attic are roll or blown insulation. Roll insulation is constructed like a foam mat, or batting, and requires less specialized equipment to install. The process is simply to cut it to the correct size and staple it in place. Blown insulation consists of loose fluffy pieces of material. It can be installed professionally or you can rent a blowing machine and do it yourself.

Once you've selected the material to insulate an attic, it's important to calculate how much is needed. Depending on the climate, specific minimum R-values are recommended for maximum benefit. The R-value is a rating that indicates the resistance to heat transfer provided by the insulation. Attic insulation with higher R-values allows less heat transfer and conserves more energy. Once you've chosen the desired R-value, calculate the amount needed based on the attic measurements.

The next step to insulate an attic is preparing the space. This includes sealing any air leaks; pay special attention to the area near the attic stairs and other openings. Install metal flashing around heat sources such as the chimney or light fixtures to maintain at least 3 inches of clearance for fire safety reasons. If the attic is unfinished, consider laying down boards to walk on so you don't step through the ceiling of the room below.

Once the space is ready, apply the insulating material. With roll insulation, the material should be cut to fit the space in long strips and then stapled in place. It should be installed in the space between floor joists first; another layer can be placed over that for complete coverage. With blown insulation, the bags of insulating material should be loaded into the machine one at a time; the insulation is then blown out of the machine through a hose. Remember to direct the hose so that the insulation is spread out evenly including all corners until the desired thickness has been applied.

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Discussion Comments


@Feryll - If you don't feel comfortable blowing in or paying the insulation yourself then consider going down on the thickness of the insulation. Even if you fall short of the recommended thickness you will still see benefits in energy bills. You can tell whoever is going to do your attic insulation that you only want half of the suggested depth of insulation-- or three quarters or whatever you can afford at that time. Then when you have more money you can go back and add more insulation.


@Feryll - I know this doesn't help you now because you have already replaced the windows, but don't replace anymore until you have the attic insulated. If you had started with the attic insulation you might have seen that the windows weren't the problem. They seldom are unless the windows are falling apart or are missing glass panes.

As far as installing the attic installation, follow the guidelines given in this article, take your time and be sure to hit all of the air holes and you should be fine.


I just got an estimate for insulating our attic from a representative of a local insulation company. Our house is more than 2,500 square feet, but I still had no idea the cost would be so much. The estimate included the sealing of all of the air holes like those around the electrical wires and the attic door, but still the price was more than we budgeted.

I think I could get the attic insulated with the help of a friend, but I'm not sure we have enough experience to do the job so that we will be saving as much money as possible on energy. Right now, the heating bills are outrageous, and we have already replaced a large number of windows, which was also expensive.

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