Vapor Retarders: 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 switch plates.
Air Retarders: 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 "house wrap" 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.
Installation: 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 "two-hole 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.
Cost: At the time this publication was written, the average loose-fill insulation cost per R-value per square foot was about 0.8 cents for cellulose and Rockwool and 1.1 cents for fiberglass. These prices were for materials only. The average installed price per R-value per square foot was about 1.2 cents for blown-in cellulose and Rockwool and 1.3 cents for fiberglass. Because prices vary in different regions, obtain bids from several insulation contractors or suppliers to determine the specific cost in your area.
Installation Quality Control: Voids and Gaps - To ensure a quality installation, there are several things to watch out for when installing loose-fill insulation-whether you do the job yourself or hire a professional.
You may create undesirable voids or gaps if you install the insulation at too low a density or if you do not completely fill the cavity. Voids are most likely to occur at the top of wall cavities, above windows, around doorways, and in the corners of ceiling cavities. Voids also occur if the installation holes are improperly located between the vertical framing studs or if there are too few fill holes. Keep in mind, though, that installers practices may vary regarding the number, location, and size of installation holes.
It may be difficult to achieve recommended R-values with loose-fill insulation in the eave area of the attic. There are insulation techniques that can be used to insulate this area adequately.
Fluffing: "Fluffing" occurs when insulation is installed to minimum thickness but not to minimum weight requirements. The result is a less dense application of insulation that requires fewer bags. When insulation is "fluffed," air passes more easily through it. This means increased heat loss. Additionally, the fluffed loose-fill insulation will eventually settle and result in a thinner layer with a lower overall R-value. Fiberglass is more "fluffable" than cellulose or Rockwool.
Intentional fluffing by unscrupulous contractors has been a problem in some parts of the country. To avoid these problems, compare bids from several contractors to see how many bags they specify. Count the number of bags used during installation, either by you or a contractor, and compare it to the instructions on the bag. The manufacturer should specify the amount of insulation required to obtain a particular R-value per square foot (or square meter) of space.
Safety and Health Concerns:
Insulation blown into your ceiling cavities should cover the top plate of the wall, but be sure the eave vents are not covered. These vents provide necessary ventilation to your attic, and covering them could result in severe moisture problems.
Electrical devices and recessed lights (except "IC-rated" fixtures) require 3 inches (8 centimeters) of clearance from insulation.
Pipes for kitchen stoves, wood stoves, and furnaces should only be insulated with fiberglass or Rockwool because cellulose may smolder if flue temperatures become hot enough.
Some observers contend that fiberglass particles can cause cancer if inhaled, and others state that the fire retardants and insecticides added to cellulose may be harmful to breathe. While the debate continues as to the health effects of loose-fill insulations, it is important to protect yourself when installing any type of insulation. Wear a quality respirator, and wear protective eyewear and clothing such as goggles, gloves, long-sleeved shirts, and pants to minimize contact with the insulation.
Insulation fibers can also be drawn into air distribution systems if the ducts are not properly sealed, allowing the fibers to circulate within the living space. Be sure to seal all of your home's ductwork, as well as any other openings where insulation could leak out of the wall or ceiling cavities and into your living space.
Cellulose, fiberglass, and Rockwool loose-fill insulations are good choices for many insulation projects. However, they are not suitable for all situations. Conduct careful research and consider factors such as your climate, building design, and budget when selecting the best insulation for your specific circumstances. If you control air leakage and ensure that the insulation you select is installed properly, you can reduce your energy bills and enjoy a more comfortable home. For information on insulation installation techniques and on other ways to weatherize, to select materials, and to make your home more energy efficient, contact EREC.