Heating and cooling your home takes a large portion of your energy budget. Roof insulation can help keep your energy costs down. While it's easiest to install insulation in a new home, there are a variety of insulation types that you can add to an older home to improve its energy efficiency.
R-Value
The R-value measures the effectiveness of any type of roof insulation. Insulation types with higher numbers provide better insulation. The appropriate R-value depends on the location of the house. In a milder climate, insulation with an R-value of R-19 is sufficient. Cooler climates need at least an R-30 in the roof and attic areas. The coldest climates need between R-38 and R-49 for maximum insulation benefits.
Foam Board
A number of different types of foam board are available to use in roof insulation. All are effective insulators. Some products are suitable to use as roof sheathing underneath shingles, while other foam boards attach to the rafters on the inside of the house. Many municipalities require interior foam board installation to have a covering of plywood or gypsum board over it. While foam board has flame retardants in the foam, if it does catch on fire, it burns quickly. It's for that reason that building codes require a covering over it as an extra layer of safety.
The most common types of foam board are molded expanded polystyrene (MEPS) and extruded expanded polystyrene (XEPS). Both are a closed-cell material that mixes plastic beads with other chemicals to form a liquid. A machine then injects the liquid into a mold that forms sheets. XEPS is a heavier-duty product, provides a greater R-value and costs more to purchase.
Polyisocyanurate, or polyiso, is a third type of foam board. It's thinner than MEPS and XEPS. Polyiso retains its shape better under extreme heat and cold, which makes it a good choice as roof insulation.
Spray-on Foam Insulation
Spray-on foam insulation works well to fill in all the nooks and crannies between rafters. It's a good choice for new construction. Spray foam insulation provides a high R-value. Because it requires special equipment and special handling, it's best to hire a contractor to apply this type of insulation.
Considerations
Ventilation and moisture control are issues with any type of insulation, but especially when dealing with the extreme temperatures possible in a roof. Without proper ventilation, the home's air quality may deteriorate. Vapor-retardant paper is often necessary on the warm-in-winter side of the insulation. Without a vapor barrier, water may condense between the insulation and the rafters and begin to cause the rafters to rot. It's possible to buy foam board insulation that already has the vapor barrier installed.
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