Upgrading the level of your attic’s insulation makes a wonderful difference in both comfort and energy efficiency, and in most homes it’s also fairly easy to do. Here are some step-by-step suggestions for retrofitting attic insulation:
1. Check the level of your existing insulation. Take a trip up into the attic with a flashlight and a tape measure. Check the level of the insulation by probing down with your tape measure until the end of the tape touches the ceiling (be sure you’re not measuring to a ceiling joist, electrical box or other raised area hidden beneath the insulation). Try to probe the insulation in several different areas so you’re sure that you have a good, accurate average of the insulation’s depth across a reasonable area of the attic.
For most homes, an R-value of R-38 is required by code, and colder areas can benefit from increasing that to R-49. To get an idea of how much insulation you currently have, multiply the thickness of what’s existing by the R-value per inch shown in the following chart:
So for example, suppose you have about 6 inches of loose fiberglass in the attic. The R-value would be approximately 15 (6 x 2.5), and you could definitely benefit from the addition of some insulation.
2. Determine what kind of insulation you want to install. There is no “perfect” insulation for your attic. Much of your choice will come down to what’s existing and whether or not you want to do the work yourself.
If you want to do your own work, you basically have two options: batts (fiberglass or mineral wool) or blown-in cellulose. Batt insulation comes in rolls of standard widths that are designed to fit between the ceiling joists. They may be faced, meaning they have a vapor barrier attached to one face, or unfaced, with no vapor barrier. Batts are a good choice for an uninsulated attic, where you can lay them between the joists, or for an attic that is already insulated with batts, where you can install a new layer of unfaced material over and perpendicular to the first layer. Batts do not work well over existing blown insulation, since they will lay unevenly with lots of gaps, and will also compress the old insulation to some degree.
Cellulose insulation can be purchased at most home centers, and they will loan or rent you the blower so that you can blow it in yourself. You can blow cellulose into uninsulated attics, or over existing insulation to form a deeper layer. Cellulose lays down well and tends to seal off drafts and cold spots well, but it is a little more prone to packing down. Also, some of the older blowing equipment available does not inject enough air into the insulation as its blown, which can reduce its R-value.
If you do it yourself, be sure to follow all of the manufacturer’s instructions for safety precautions, including proper clothing and protection against breathing in dust and fiber.
Perhaps the most common choice for attic insulation is blown-in fiberglass. This requires large, heavy-duty blowing equipment, and needs to be left to the pros — which is fine, since most people choose not to do their own attic insulation anyway. Fiberglass does not have as high of an R-value per inch when compared to blown cellulose so a greater depth is required, but it tends to hold its loft better over time.
3. Check ventilation and fire safety. Whether you’re insulating the attic yourself or having an installer do it for you, there are certain precautions that need to be taken.
Heat-producing fixtures, including fireplace chimneys, wood stove flues and many types of recessed light fixtures, need to be protected from having insulation placed over or around them so that they don’t build up an excess amount of heat. Use sheet metal to construct dams around these areas as needed, creating a 1- to 3-inch air space as per the manufacturer’s recommendations.
Use vent baffles to keep the insulation from sloughing down over vents, which will block their air flow and partially or completely negate their effectiveness.
Finally, be sure all exhaust fans are vented completely to the outside of the attic! In fact, even if you are not re-insulating your attic, in order to prevent structural damage and the potential for mold growth, you need to make sure your fans are vented all the way to the outside.
Remodeling and repair questions? E-mail Paul at firstname.lastname@example.org.