Save about $600/year by boosting the amount of attic insulation from R-11 to R-49.
Depending on the type of materials you use, figure on paying an insulation contractor about $1,500 to insulate an 800-square-foot attic, which pays back your investment in three years. You’ll spend about half that to do the job yourself.
Do You Need More Attic Insulation?
A good, quick way to check if you need insulation is to look across your attic floor. If the existing insulation comes up just to the tops of the joists, then you probably need to add insulation. If you can’t see the joists and the insulation is well above the tops of the joists, you’re probably okay and you won’t recoup the cost of adding more.
Methods for Insulating an Attic
Add insulation to your attic one of three ways:
Roll-on or blanket-type insulation comes as rolls of fiberglass batts, either 15 or 23 inches wide—designed to fit between the width of typical framing. If your attic already has some insulation in the attic floor, roll out the batts at right angles to insulate over the framing members.
If you’re doing the job yourself, blanket-type material is easiest to work with. Be careful not to compress it or it won’t be as effective.
Loose-fill or blown-in insulation requires a machine that shoots a stream of loose-fill cellulose over the existing attic floor framing. This is typically a job for an insulation contractor. The advantage is that loose-fill insulation does a great job of filling in small crevices and other hard-to-reach areas.
Sprayed foam polyurethane is a good choice if you plan to turn your attic into a finished room. In that case, you’ll want to insulate the roof—not the floor. Sprayed foam polyurethane molds to rafters, blocks water vapor, and has a high R-rating per inch. Expect to pay about double the per-square-foot cost of roll-on and loose-fill insulation.
Related: Attic Air Leaks: How to Find and Seal Them
How Much Attic Insulation Is Enough?
To determine how much to add, look up the recommended amount for your area, then subtract the value of your existing insulation. If you don’t know, you can figure it out using the Home Energy Saver online energy audit tool.