How to install fiberglass batt insulation | ProConstruction Guide
How to install fiberglass batt insulation

How to install fiberglass batt insulation

Gently press the insulation into the opening between the wall studs

Gently press the insulation into the opening between the wall studs so it fully contacts the exterior wall or the drywall—pay special attention to corners and edges.

Installed in attics, basements and crawl spaces, fiberglass batt insulation can improve winter heating and summer cooling. Here is how to install fiberglass batt insulation.

A home remodel or room extension should include installation of fiberglass insulation batting.

However, quality installation performed by a professional is the only way homeowners can ensure they get the maximum benefits from the new insulation.

The Federal Trade Commission (FTC) mandates that each package of insulation carry a label that includes its R value, or resistance to heat loss. The higher the R value, the greater the resistance to heat loss. Choose batt insulation rated for your specific area. Insulation manufacturers have maps showing R values across the country on their web sites. As a rule, use R30 or R38 for ceiling and attic spaces, R13 to R21 for exterior walls and R11 for interior walls.

Fiberglass batt insulation is a rectangular piece of insulation, usually made of fiberglass that is 8 or 9 feet long. Insulation is also available in rolls that you can cut to custom lengths. Batt insulation is available with or without facing, or with a fire-retardant foil covering for areas that will be left exposed, such as in garages or basements. Batts are sized for the application.

To determine how much insulation to buy, measure floor to ceiling and multiply by the number of between-the-studs spaces you need to fill. To calculate the number of batts you need, divide that total by the length of the batt (usually 8 feet). Then measure the distance between the studs; that’s the width of insulation you need. For example, if the studs are on 16-inch centers, use 16-inch batt.

A top-quality fiberglass batt insulation installation requires just a few basic tools: a utility knife with a good supply of sharp blades, a tape measure, a straightedge, a lightweight stapler or hammer tacker, and a 3- or 4-inch putty knife.

Fiberglass can irritate your throat and skin, so wear protective gear. Never handle insulation without wearing a two-strap mask rated for fiberglass insulation, a hat, heavy-duty work gloves, a long-sleeve shirt and goggles to keep fibers out of your eyes.

Installing fiberglass batt insulation

Step 1

To install fiberglass batt insulation, gently press the insulation into the opening between the wall studs so it fully contacts the exterior wall or the drywall, paying special attention to corners and edges. Then pull it back slightly to “fluff” the insulation so it fills the space completely. Never compress the insulation or leave gaps, which reduce the efficiency.

If you’re working with 8-foot batts, you won’t have to trim for length. To cut batt to fill a narrow space, use a long straight edge and a utility knife. Make the cut about ½-inch wider than the area so when it is installed, it will fill the area and stay in place.

Step 2

Batts without facing should fit snugly with no voids, and should stay in place without stapling, held by friction against the stud. Faced insulation may have stapling flanges — extra facing on each side — that allows you to staple it to the side of the wall stud. Do not staple to the face of the studs to avoid problems when drywalling.

Where electrical wiring crosses the space, split the batting in half

Where electrical wiring crosses the space, split the batting in half and install half behind the wiring and half over the top.

Step 3

Cut faced batting face down on a cutting surface. Compress the batting with the straight edge while making the cut. If cutting in place, cut against the mid-line of the stud. This will give you adequate overlap to hold the batt in place.

Step 4

Where electrical wiring crosses the space, split the batting in half and install half behind the wiring and half over the top. For switch and power outlet boxes, cut the batting carefully so it is snug against the sides of the boxes. Be careful not to cut into the wiring insulation.

To install fiberglass batt insulation in tight spaces, use a wide putty knife

For tight spaces, such as the shimmed areas around a door or window, use a wide putty knife to press skinny strips of batting into place gently.

For other obstructions, such as pipes, cut slits in the batt and fit it snugly around the obstacle. Do not “stuff” insulation into around obstructions; gaps left behind the pipe or wiring can reduce the R-value of the insulation.

Step 5

To install fiberglass batt insulation in tight spaces, such as the shimmed areas around a door or window, use a wide putty knife to press skinny strips of batting into place gently. Do not over-compress the insulation.

—By Steve Sturgess, stevesturgess.com


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