There are other home weatherizing and sealing measures to complete before you undertake any insulation project. Atight, well-sealed home is more energy efficient and needs less insulation to keep you and your family comfortable. Tests have shown that far more cold air infiltration and heat loss result from improperly sealed windows, doors, ducts, light switches, and outlets than from insufficient insulation coverage or performance.
These common air leakage points should be properly sealed with caulk, weatherstripping, and insulation.
If you are adding insulation to an existing ceiling structure and a vapor retarder is not already installed, consider adding one. Generally, the vapor retarder should be placed on the warm-in-winter side of the insulation—usually the side facing the interior living space. However, in hot, humid climates (primarily the southeastern states), there is controversy over where a vapor retarder should be placed. No matter where you live, consult an insulation manufacturer and your building code official for recommendations on where to place a vapor retarder. When installing loose-fill insulations, a material such as 6-mil (0.006-inch, or 0.015-centimeter) polyethylene plastic sheeting can be used as a vapor retarder. Paints that act as vapor retarders are also available. These paints may be more practical for retrofitting homes where no vapor retarder exists because they can be installed without removing finished surfaces. Federal Housing Administration Minimum Property Standards require that any product, including paint, must have a permeability (perm) rating of 1.0 or lower to qualify as a vapor retarder. The lower the perm rating, the greater the material’s resistance to vapor penetration. For example, 15-pound (6.8-kilogram) asphalt felt paper has a perm rating of 1.0, while 6-mil polyethylene sheeting is rated at 0.06, and common household aluminum foil is rated at 0.0001. If the drywall on your ceiling or wall is removed and the insulated area is completely exposed, you can install 6-mil polyethylene sheeting. Be sure that it runs continuously along the surface area of the ceiling and walls, and that no tears occur during installation. Additionally, all penetrations, such as electrical outlets and light switches, should be carefully sealed. There are preformed foam gaskets for use behind outlets and switchplates.
An air retarder reduces energy loss because it prevents heated or air-conditioned indoor air from escaping through the building shell. It also blocks drafts of hot or cold outside air—caused by winds and pressure differences between the inside and outside of the house—that reduce your home’s comfort and heating or cooling efficiency. An air retarder is different from a vapor retarder in that it blocks only air, not moisture. The American Society for Testing and Materials specifies that a material must have a perm rating of 5.0 or higher to qualify as an air retarder. Remember, the higher the perm rating of a material, the more moisture can pass through it. An air retarder should have a high perm rating because this allows the escape of moisture that may have migrated into insulated cavities. In new construction, an air retarder (such as “housewrap” products that are now available) is often wrapped around the outside walls before installing the exterior finish, and a vapor retarder is installed around the inside walls before the interior finish is completed.
Holes used to install loose-fill insulation in walls must be properly positioned.
Loose-fill insulations are typically installed with special equipment that blows the insulation through a hose and into the cavity. Although loose fills can be installed in both new and retrofit situations, they are especially popular for retrofit projects because they can be installed with minimal disturbances to existing finishes.
Installation often calls for the “twohole method,” which entails drilling two holes spaced vertically between the exterior walls’ framing studs. The holes should be 2 inches (5 centimeters) in diameter. Working between each stud, drill one hole 16 inches (41 centimeters) from the top of the wall. Drill the other hole 24 inches (61 centimeters) from the bottom of the wall. The insulation is blown into the holes, then the installation holes are sealed. Installation is most commonly done by professionals who are experienced at operating the equipment to ensure proper density and complete coverage.
In conventional and cathedral ceilings, insulation is easier to blow in if an access opening through the ceiling already exists. Otherwise, it may be necessary to drill holes in the ceiling or between the roof rafters.