One of the easiest and most cost-effective energy upgrades you can make to your home is to improve the level of insulation in your attic. Upgraded attic insulation makes your home easier and less expensive to heat — and to cool next summer — and also makes for a more comfortable living environment.
Depending on what you have now, an insulation upgrade may be a do-it-yourself project, or it may be one that you want to leave to the pros. Some utility companies have programs in place with rebates or low-interest loans to help with energy upgrades, so you’ll want to check with them as well before you get started.
How much do you need?
How much insulation you need is always a good question. The easy answer is "as much as you can get," but actually there’s a point where continuing to add more insulation really won’t pay you back much additional dividends.
For example, if you have R-19 in your attic, doubling it to R-38 will be a huge improvement. But doubling R-38 to R-76 wouldn’t be nearly as effective.
The R-values for new homes are set by the building codes, so that’s a good place to start. Many areas have established R-38 as a minimum for attics, and some colder areas have increased that to R-49. The further your insulation is below what the codes require, the more you’ll benefit from the upgrade.
What’s up there now?
How much you’ll benefit from upgrading your insulation depends on what’s in the attic now. So you’ll want to start with a trip into the attic to determine what kind of insulation you have, and also to measure its average depth. Here are the four most common types of attic insulation:
- Loose-fill fiberglass: This is probably the most common, and will be fluffy strands or cubes of pink, white or yellow material. It has an average R-value of 2.5 per inch, so if your measurements show that you have about 6 inches of the stuff, you have an R-value of approximately 15.
- Fiberglass batts: This is the same material, but it’s woven into thick mats instead of lying loose. It’s typically lying between the joists, but it may be on top of the joists as well. Batts have an average R-value of 3.2 per inch, so your same 6 inches would give you an R-value closer to 19.
- Mineral wool: This is another loose fill material, although it’s also made into batts as well. It’s gray, and will appear thicker and more fibrous then fiberglass. The average R-value is about 2.8 per inch, so 6 inches would have an R-value of around 17.
- Cellulose: This is essentially a recycled paper material, with other additives. It’s a light to medium gray, and is a loose fill but not as fluffy as fiberglass. It has a distinct "ground cardboard" look, and averages 3.7 per inch in R-value. Six inches of this material would give you an overall R-value of about 22.
What type of insulation to install?
What type of insulation you’ll want to use for the upgrade depends on a couple of different things, including the costs in your area, and whether you want to do the work yourself.
For attics, blown-in insulation works best. It’s easy to install, covers everything to a uniform depth, and is cost-effective. If you want to do the work yourself, both fiberglass and cellulose can be blown in using a blower that you can rent. Many home centers and other insulation retailers have the blowers available, and they’re sometimes loaned free of charge with a minimum insulation purchase.
Either of these types of insulation produces a lot of dust as they’re being blown, so you’ll want to wear a respirator, as well as some eye protection. For a complete list of safety gear, safety precautions and installation tips, refer to the manufacturer’s specific instructions.
The other alternative is fiberglass or mineral wool batts, which come in standard widths and thicknesses. These work best for attics that don’t have any insulation at all, since you can lay the batts between the joists. If there’s already batt insulation in place, you can install a second layer over the first. Use unfaced batts only, so that you don’t create a double vapor barrier and trap moisture between the layers of batts. Also, install the new layer perpendicular over the original layer, for better coverage over any gaps and cold spots.
You need to keep the insulation away from anything that produces heat, such as fireplace chimneys, wood stove flues and exhaust fans. Recessed light fixtures can only be covered if they’re specifically rated for that purpose. To keep the insulation away, use sheet metal to construct a dam, creating a 1- to 3-inch air space as per the insulation or fixture manufacturer’s recommendations.
It’s also important that you don’t do anything to block the ventilation in your attic, so you also need to install vent baffles to keep the insulation from sloughing down over soffit vents. These can be wood or cardboard, attached to the face of the rafters at each of the vents to keep the air flow clear.
Finally, to prevent moisture buildups that can damage wood framing and lead to mold growth — in addition to robbing R-value from that new insulation — be sure all exhaust fans are vented completely to the outside of the attic!