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How to Install Attic Insulation

By Kris Jensen-Van Heste

A well-insulated attic will make your home warm in the winter and cool in the summer, saving you money and keeping you comfortable. Installing attic insulation is easy to do and is a relatively inexpensive home-improvement project. Here's how:

Before You Buy Attic Insulation:

The Federal Trade Commission mandates that each package of insulation carry a label that includes its specific R value, or resistance to heat loss, as well as health and safety precautions. The higher the insulation's R value, the greater its resistance to heat loss.

Which R value is right for you? That depends on several things, including where you live and what type of heating system you have. The US Department of Energy has created an online zone map with corresponding R values to help homeowners determine minimum insulation values. The DOE's ZIP Code Insulation Program website also can help you determine how much insulation you'll need based on your ZIP code.

Kinds of Attic Insulation:

You can buy insulation as loose fill or in blanket form. Loose fill is forced through a tube and blown into the space, so it's great for an attic, but it requires professional installation. That leaves blanket insulation for the do-it-yourselfer; blanket insulation is available as batts or rolls.

A batt is a rectangular piece of insulation, made from fiberglass or mineral fibers, usually 8 feet long (a standard ceiling height), and sold flat in packages. Rolls come in varying widths, typically 16 or 24 inches. Both are sized to fit between studs and joists, so be sure to measure the space between the attic joists before buying.

Insulation Vapor Barrier: Which Way to Face It?

Though insulation can either be covered with a facing material or left open-faced (meaning the fluffy fibers are exposed), unfaced insulation is the best choice when adding to existing attic insulation.

For an uninsulated space, faced insulation is best. Brown Kraft paper is a common facing, and it also serves as a vapor barrier, keeping condensation off your insulation. Install this type of insulation faced-side down.

Tip: Learn More About Attic Insulation Vapor Barriers

Insulation backed with a fire-retardant foil is another good choice for improved thermal-blocking and fire-retardant abilities. As with any other vapor barrier, be sure to install the insulation with the barrier facing the conditioned space (in other words, downward).

Buying Attic Insulation:

To calculate how much insulation you'll need, measure the length of each row of space between attic joists, and add the figures. Then divide by the length of insulation you're buying, whether it's 8-foot batts or 25-foot rolls. That will give you the number of packages you'll need. Buy a little extra; you can always return unopened packages.

If you have no insulation in the attic space yet, you'll want an R value of at least 38.

If you've got some insulation already, consult the Department of Energy chart for the correct R value. If the existing insulation is worth keeping, but you want to add to it, buy only unfaced insulation, and don't exceed 12 inches of combined thickness. Here's how to calculate how much insulation you'll need:

  1. Measure the thickness of the current insulation.
  2. Seven inches of fiberglass or rock-wool insulation provides an R value of 22, as does 6 inches of loose-fill insulation. Those figures, provided by the U.S. Department of Energy, will give you a good estimate of your current R value if your insulation isn't labeled.
What You'll Need to Install Attic Insulation:
  • Insulation (batts or rolls)
  • Measuring tape
  • Utility knife
  • Filter mask or respirator
  • Safety glasses
  • Gloves
  • Long-sleeved shirt and long pants
  • Knee pads (optional)
  • Work gloves

How to Install Attic Insulation:

This is a very straightforward job, easily done by one person.

  1. Begin at one end of the attic space, being careful to keep your weight on the joists if they're open.
  2. Unroll the insulation or lay the rectangular batts carefully between the joists, taking care not to compress them.
  3. Butt the ends of the batts or rolls together as tightly as you can without buckling the insulation; any gaps will severely compromise the insulation's R value. No staples are necessary; gravity holds it in place.
  4. Trim with a utility knife where needed.

It's very important to keep the insulation at least 3 inches away from any recessed fixtures or wiring - that could pose a serious fire hazard.

Tips

  • You may find it easier to work in an open-joist area if you can bring at least a 3-foot-by-3-foot piece of ¾-inch plywood into the attic with you. Kneel on it as you work, resting it on the joists to keep you from putting your foot through the dry-walled ceiling just below you.
  • When you're finished, launder your work clothes in a load separate from your regular wash and run the rinse cycle twice.

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