Determining your attic’s insulation needs.
To determine if you need more attic insulation, find your zone and the recommended R-value for your attic.
U.S. Department of Energy Recommended* Total R-Values for New Houses in Six Climate Zones.
* These recommendations are cost-effective levels of insulation based on the best available information on local fuel and materials costs and weather conditions. Consequently, the levels may differ from current local building codes. In addition, the apparent fragmentation of the recommendations is an artifact of these data and should not be considered absolute minimum requirements.
A. R-18, R-22, and R-28 exterior wall systems can be achieved by either cavity insulation or cavity insulation with insulating sheathing.For 2 in. 4 in. walls, use either 3½ in. thick R-15 or 3½ in. thick R-13 fiber glass insulation with insulating sheathing.For 2 in. x 6 in. walls, use either 5½ in. thick R-21 or 6¼ in. thick R-19 fiber glass insulation.
B. Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, and all ventilation to the crawl space is blocked.A vapor retarder (e.g., 4- or 6-mil polyethylene film) should be installed on the ground to reduce moisture migration into the crawl space.
C. No slab edge insulation is recommended.
Source: www.eere.energy.gov
Note: We generally don’t recommend retrofitting exterior wall insulation, because the payback can be delayed for many years. The exception to this is new home construction, where insulation with at least an R-15 rating is recommended in the exterior wall cavity.
Choosing insulation materials
The two most common types of attic insulation are batt form (cotton or fiberglass batts) or loose fill/blown in insulation (cellulose, fiberglass, rock-wool and cotton). Cellulose is recycled newsprint treated with a fire retardant. Fiberglass is thin fibers of glass that trap air.
Batt insulation can be used in knee walls to protect the side of the wall that has conditioned space. Blown-in or loose-fill insulation should be installed in uniform thickness across the entire ceiling surface area of the attic.
Do-it-Yourself Versus Hire a Pro
Installing batts and rolls in attics is fairly easy, but doing it right is important.Make sure the insulation you install is tightly sealed, and follow the manufacturer’s instructions.
If you decide on loose-fill fiberglass or cellulose, consider having a professional install the material. The equipment the pros use blows in material at the correct density. If you decide to install loose insulation yourself, always refer to the manufacturer’s instructions, especially regarding minimum thickness and minimum weight per square foot to achieve the desired R-Value.
