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Insulating Finished and Unfinished Walls




Finished Walls
Blown-in loose? fill wall insulation for finished walls is not recommended for do-it-yourself application. This measure is difficult to install and has some health and safety concerns which should be considered. We suggest you hire a professional installer to do the weatherization work. Your utility can assist you in finding a qualified installer.

Unfinished Walls
Unfinished walls are those without gypsum board or other material covering the studs. They are usually found between the main part of the house and an attached garage or utility room, in an attic, or in the basement. These walls can be easily insulated simply by pushing batt-type insulation into each stud space.

To Insulate An Unfinished Wall, You'll Need:
  • Protective Gear: Wear loose-fitting clothing, cotton gloves, and a respirator.
  • Insulation and Materials
  • Enough R-11 vapor barrier-faced batt or blanket insulation to cover the area of the wall. If you use insulation without a vapor barrier facing, you must install some other type of vapor barrier (1.0 perm rating or less) such as low-perm paint, foil wall papers, or polyethylene.
  • For "furring out" masonry walls, enough 1 x 4 boards ("furring" strips) to space 24 inches apart across the perimeter of the wall and to extend horizontally across the wall at both the top and bottom (for the top and bottom plates)


Tools and Equipment:
  • Staple gun and staples
  • Sharp knife
  • Straight edge and soft lead pencil
  • Tape measure
  • Duct tape
  • Hammer and nails


Measuring and Cutting Insulation For Walls
Measure slabs of insulation the length of the stud space plus 2 inches, to assure a tight fit. Use a straight edge and a sharp knife to cut the insulation, facing side up.

Peel back insulation 1 inch at the top and bottom of facing. This forms a stapling flange. (If you are using 48-inch precut batts, it will only be necessary to peel back the insulation at one end.)

Insulating Unfinished Wood Frame Walls
The way that you install insulation in an unfinished wall depends on whether the unfinished side faces a heated space or not. The vapor barrier must always come between the heated space and the insulation, to protect it from moisture produced by the household activities.

Insulating An Unfinished Wood Frame Wall In An Unheated Space
Some common places to find unfinished walls in an unheated space are garages and unheated utility rooms which adjoin heated basements. Knee walls in heated attics can also be insulated on their unfinished side, which faces the rafter space. (Fig. 6.1.)

Measure and cut insulation slabs as described above. Starting at the top of the stud space, push the batt into place. (Fig. 6.2.) The vapor barrier faces against the wall. Because the insulation is cut slightly larger than the stud space, it should fit snugly. An alternate method of holding the insulation firmly is to string 4 or 5 wires across the wall's width, attaching them to nails at either end as shown in Fig. 6.2.

If the wall faces the living space, it should be covered with gypsum board sheathing or other fire-retardant paneling, with taped and sanded seams. The only exception to this is when non-combustible insulation is used, with a vapor barrier facing which has a flame spread rating of 25 or less. Your utility can refer you to local building codes on application of paneling.

To insulate unfinished knee walls in a heated attic, you must gain access to the rafter space. This may require cutting out an access hole, for which you may want to hire a contractor.

Lay walking planks between the joists, as described on page 8-9 Insulating the Ceiling.

Insulate the collar beams and knee walls as shown in Fig. 6.3. When insulating knee walls, the vapor barrier faces away from you, as you work, toward the heated (attic) space.

If you are insulating a finished attic with this method, you must also blow in insulation over the attic ceiling, as discussed in Section III.

Insulating An Unfinished Wall Facing A Heated Space
The vapor barrier will face toward the room in installations of this type.

Starting at the top of the stud space, push the batt into place (Fig. 6.4). Stapling flanges should be overlapped to provide a continuous vapor barrier.

The same staple can be used to fasten overlapping flanges from adjacent batts onto the top of the joist. Be careful not to catch any insulation in the stapling flanges, or a bulge may be visible when the wall is covered with gypsum board sheathing.

Beginning at the top of the stud space, pull the flange to the top plate and staple three or four times along the top. Staple the sides every 3 to 5 inches. Staple along the bottom flange 3 or 4 times.

Fitting Irregular Spaces
In spaces narrower than 16 inches, cut the blankets down to allow a 1-inch stapling flange on either edge. Peel the insulation back 1 inch to form the stapling flanges. Face the vapor barrier toward the heated space.

Spaces wider than 16 inches on center can usually be insulated by cutting down 23-inch batts (Fig. 6.5). Spaces wider than 24 inches on center can be insulated by placing bans horizontally and stapling into place on the inside of the joist.

To prevent water pipes from freezing, compress insulation between the pipes and the exterior walls (Fig.6.6). Insulation should be fitted behind heating ducts to stem heat loss and pushed as much as possible behind electrical boxes (Fig. 6.6). Take care to avoid tears in the vapor barrier. Repair any existing tears with duct tape.

Unfinished walls should be covered with gypsum board sheathing or other fire-retardant paneling, with taped and sanded seams. The only exception to this is when non-combustible insulation is used, with a vapor barrier facing which has a flame spread rating of 25 or less. Your utility can refer you to local building codes on application of paneling.

Insulating Unfinished Concrete Walls
Masonry walls are usually located in unfinished basements.

To insulate these walls, you must install lumber "furring strips" onto which the insulation is stapled and finish wall material is applied. (The cost of "furring" walls is not covered in this program.) Though this job is not complicated, it does require some carpentry skills. You may wish to consult a basic carpentry book in addition to the general instructions given here.

Many find it easiest to construct a wood frame on the floor and then stand it up in place. (Fig. 6.7.) To do this, you must make sure your measurements are exact.

Cut studs the height of the wall, minus the depth (approximately ¾ inch each) of the top and bottom plates. Nail the studs to the top and bottom plate as shown in Fig. 6.7, so that the space from center to center of each stud measures 24 inches. Stand the frame up and attach to the wall.

Install insulation as described for frame walls. Cut separate pieces of insulation to fit between the top plate and the subflooring. (Fig. 6.8.)

You may also install foam board insulation on concrete walls (Fig. 6.9).

When installing foam board, you should "fur out" the walls, even though the board can be applied directly to the masonry using mastic. Foam board is highly flammable and must be covered with a fire retardant finish material (such as ½ inch gypsum board or paneling) after installing. The finish material is installed by nailing it to the furring.

"Fur out" the walls as described and glue foam board between the lumber furring strips. Cut the board to fit using a sharp knife. Be sure to install a vapor barrier (6-mil polyethylene or vapor barrier paint) if insulation is unfaced (Fig. 6.10). Finish according to local building codes for the application of paneling. Information is available from your utility.

Next: Weather-Stripping and Caulking


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