Insulating a New Space

Insulation not only makes new living spaces feel comfortable but also cuts heating and cooling costs. It comes in two basic forms for unfinished walls or ceilings: blankets or batts, consisting of bundles of fiberglass or mineral fiber attached to paper or metal foil, and rigid insulating boards or panels.

Insulating Fiber: Blankets come in long rolls, batts in precut rectangles, usually 4 or 8’ long. Both come in varying thicknesses and in 14.5” widths to fit between joists or studs. It is a good rule to install the thickest insulation you can fit between joists and studs without having to compress it.

Both blankets and batts can be purchased with a vapor barrier of chemically treated or foil-lined paper that prevents the moisture-laden air of a heated room from penetrating the insulation material. Blankets and batts for use between studs and rafters usually come with stapling flanges at each side to make installation easier. Friction-fit batts, usually used between floor joists, do not have flanges.

Thermal Panels: Rigid panels of polystyrene insulation are often used on masonry walls such as those found in basements. These 4-foot-by-14 panels are relatively expensive but are especially efficient insulators, are easily installed between furring strips, and do not require vapor barriers.

TOOLS:

• Tape measure
• Serrated knife
• Staple gun
• Stepladder
• Duct tape
• Hammer
• Saw
• Plumb bob
• Carpenter’s level

MATERIALS:

• Insulation batts or blankets
• Insulating panels
• Scrap board (1 x 4)
• Interior plywood (0.25”)
• Box hinges
• Foam weather stripping
• Furring strips (1 x 2)
• Cut masonry nails (2”)
• Mastic adhesive

SAFETY FIRST: Wear long sleeves, work gloves, a face mask, and safety goggles when working with fiberglass insulation.

106 Insulating an attic floor.

To prevent heat loss through the floor outside a new attic room, place blankets or batts between the floor joists beyond the knee walls.

• Using a board to compress the material along the cutting line, trim blankets or batts to run from the wall to a point just short of the soffit vents in the eaves. These vents must be kept clear for attic ventilation.

• Lay the fitted blankets or batts between the joists with the vapor barrier side down.

107a A Box to Cover Openings: Weather-seal the opening into your attic to maintain the integrity of the insulation in that space. For a simple attic hatch, apply foam weather stripping along its edge and staple a ban of insulation to its attic side. For attic stairs, build a box of plywood covered with insulating balls. A lighter-weight but more expensive version of this box consists of a wood frame covered with rigid polystyrene insulation. You can slide the box out of the way as you climb the stairs or, if space permits, hinge the bottom edge of the box to an attic joist so you can tip it aside. Apply weather stripping foam along the edge of the stair opening to complete the insulation.

107b Insulating between studs and joists. Fit insulation between studs or ceiling joists, vapor barrier side facing into the room. Staple flanges at 6” intervals to the inside faces of flanking studs or joists. (Stapling them to the narrow edges of the studs makes it difficult to achieve a smooth wall surface over the studs.)

In attic knee walls, fit insulation so it meets the insulation placed between joists, so warm air can't escape. Similarly, make sure insulation fits tightly without compressing it at the knee wall/stud rafter joint.

For attic ceilings, cut blankets to rafter to-rafter measurements with about an inch extra on each end. Notch each end to fit the junction of collar beam and rafter; staple at 6” intervals to the collar beam.

108a Insulating between rafters. Select a blanket or batt thickness that allows at least - inch of space between the insulation and the roof sheathing, so that air can circulate freely from eave and ridgepole vents.

• Starting where the rafter is intersected by the ceiling collar beam, staple the blankets, vapor barrier side facing you, firmly to the inside faces of rafters at 6” intervals. Allow a slight overhang at the bottom to fit behind the knee wall insulation.

• With plastic tape or duct tape, cover the seams where the rafter insulation meets the ceiling and knee wall insulation.

108b Insulating a masonry wall.

• To make a furring grid, measure across the top and bottom of the wall and cut two 1 -by-2 wood strips to this length.

• On the wide face of one end of a strip, mark off a box 1” wide. Make similar marks at 16” intervals measured from the center of one mark to the center of the next, making the last mark flush with the opposite end, even if it's not a full 16” from the previous mark.

• Lay the two strips side by side and copy the markings from one to the other. Nail one strip across the top of the wall, the other across the bottom, using 2” cut nails at 2.5” intervals.

• Measure the distance between the two strips and then nail 1 -by-2s of this length from the top marks to the bottom marks with 2” cut nails, using a plumb bob in order to make sure that the strips are perfectly vertical.

• Cut additional 1 -by-2s to make frames around windows or doors. To complete the grid, cut 1 -by-2s into 14.5” lengths and nail them horizontally between the vertical strips, 4’ above the bottom strip. If necessary, use a carpenter’s level to check the horizontal alignment of the strips.

• Fit insulation panels between the vertical and horizontal fur ring strips, applying mastic adhesive evenly around the edges and in an X pattern across the center to secure them in place.

• Save any trimmed panel scraps for piecing around windows or doors.