Kraft-faced, or paper-faced, insulation comes in batts and long rolls. The batts are precut to fit into cavities on standard 8-foot-high walls. Roll insulation is best for floors, ceilings, and roofs with a long joist or rafter bays and for tall walls. All kraft-faced insulation is easy to cut with a sharp utility knife or insulation knife. The facing has a tab (called a flange) running along each side edge of the insulation. When installing the insulation in wood-frame structures, you fold out the flange and staple it to the side (or front edge) of the framing to secure the insulation. Kraft-faced insulation also can be simply friction-fit into the framing cavities and not stapled in place, if allowed by the local building code.
The Purpose of Insulation Facing
The facing on kraft-faced insulation is made of kraft paper with an asphalt coating that makes the paper impermeable to water vapor. The paper creates a vapor barrier that helps keep the water vapor in the warm, moist, heated indoor air from migrating outward into the wall or other structure. For this reason, faced insulation is typically installed on the "warm in winter" side of the wall. In other words, the facing usually faces in toward the living space (or into the attic or basement area, in unfinished attics and basements).
Because the facing serves as its own vapor barrier that traps moisture inside a building, it should not be used with additional vapor barriers.
How to Install Kraft-Faced Insulation
Always follow the insulation manufacturer's specific installation instructions, and be sure to adhere to local building code requirements. Codes in some areas may require you to staple the insulation flanges on the front (exposed) side of the framing to create a continuous vapor barrier. In very humid climates, building codes may not allow faced insulation at all.
The basic installation steps are the same for walls, ceilings, floors, and roofs in wood-frame houses:
- Cut the insulation roll or batt to fit the length of the framing cavity, if necessary. Place the insulation with the facing side down on a piece of scrap plywood. Set a T-square or metal straightedge over the insulation and press it down firmly. Cut along the edge of the square with a utility knife, cutting through the insulation material and the paper facing.
- Fit the insulation into the framing cavity, starting at the top (for walls) or at one end (for ceilings/floors/roofs). Gently push the insulation into the cavity, but do not force it or compress it, which reduces its insulating value. The insulation should fit snugly into the cavity with no gaps or spaces, filling it from top to bottom (or end to end).
- Fold out the paper flange along one side of the insulation. Position the flange flat against the side face of the wall stud (or floor joist or roof rafter) so the edge of the flange is flush with the interior edge of the stud, joist, or rafter. Staple the flange to the side of the framing member with staples spaced about 12 inches apart (or as directed by the manufacturer). Repeat to fasten the other side flange.
Note: Some building codes may require you to fold the flanges over the front edge of the framing and staple them to the front edge. In this case, you overlap the flanges of the insulation in neighboring framing cavities.
- Insulate behind plumbing pipes or electrical wiring running through a cavity by peeling the insulation apart to create two layers. Place the unfaced layer behind the pipe or wiring, then place the faced layer over the pipe or wiring. If there is an electrical box or plumbing fitting in the cavity, cut out the faced layer (including the face paper) to fit snugly around the obstruction.
R-Value and Kraft-Faced Insulation
The effectiveness of insulation is indicated by its R-value rating. The higher the R-value number, the better the insulation resists the transfer of heat through the insulation. It is a popular misunderstanding that insulation adds heat to an insulated space. In reality, all it does is slow the migration of heat from the warm side of the insulation to the cold side. The R-value of kraft-faced insulation typically is printed on the kraft paper facing.