The process of heating and cooling your home isn’t a cheap proposition. With rising energy costs, most homeowners are looking for ways to reduce their utility bills. Attic insulation is like a thermal blanket covering the top of your home. Not only does attic insulation reduce heat loss in the winter, but it reduces heat gain during summer months when the hot sun beats down on the roof. Reinforcing your attic’s current insulation can save money and increase your home’s “green appeal.”
The effectiveness of insulation is determined by its R-value, or thermal resistance factor. The higher the R-value, the greater the insulating factor. Not all homes require the same amount of thermal protection. In climates with mild winters, less R-value is necessary to maintain a comfortable indoor environment than is required in cold climates. When adding insulation to an existing attic, the R-value of the current insulation plus the R-value of the new insulation is added to arrive at total thermal protection value. For example, if your attic currently has R-20 insulation and you add R-15 insulation, the result will be an attic with R-35 thermal protection.
Types of Attic Insulation
Batt-type insulation is available in wool or fiberglass, and the thickness of the batt determines the R-value. Thick batts have more thermal protection than thin batts. Loose-fill insulation, which is usually blown into the attic space, can contain wool, cellulose, fiberglass or vermiculite fibers.
The general rule is to install attic insulation as close as possible to the living area. If you don’t use your attic for storage, or if you have roof trusses that crisscross the attic space, the best place to add insulation is probably at the attic floor level. Batts may be installed between the joists, or you can spray loose fiber insulation into the entire attic. If the attic is, or will be, used for storage or for future living space, the best place to add insulation is at the rafter level.
Reinforcing Attic Floor Insulation
Install paper-faced insulation batts with the paper facing downward if there is no existing insulation between the joists. If you already have a thin layer of insulation in the joists, choose unfaced batts and lay them lightly on top of the existing insulation. Batt insulation depends on “loft” for optimal thermal resistance, so don’t smash or compress the batts.
Blown-in insulation, which requires the use of a spray rig, requires uniform distribution throughout the attic to achieve the recommended R-value.
Reinforcing Attic Rafters
By installing insulation between the existing rafters, the attic space, as well as the living space below the attic, is protected. Paper-faced batts come in widths that fit between standard-spaced rafters. The batts feature tabs that fold out and fasten with staples to the rafters on either side. When the rafter space is too shallow to accommodate the thickness of the batts, you can increase the depth by attaching 1- or 2-inch boards along the bottom edges of the rafters. Called “furring,” this allows you to install thicker insulation batts for greater R-value.
Attic ventilation is essential to the health of the wood structure in the attic. Without ventilation, heat and moisture can build up beneath the roof and lead to warped rafters and roof decking. It can also shorten the life of your shingles. In an unused attic with insulation in the floor joists, block vents in the soffit before blowing in fiber insulation and uncover them once the fibers settle.
If you’re insulating the rafters, make provisions for ventilation between the batts and the underside of the roof deck. This is accomplished by attaching rafter vents, or “baffles,” to the underside of the roof deck before adding insulation. The baffles allow air to circulate beneath the batts.
Before adding attic insulation, consult an energy auditor or a contractor to determine the best type of insulation for your home’s needs.
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