Best Insulation for Ceilings

Standard Attics

• Standard attics with straight rafters are the least expensive to insulate with the best results. Loose fiberglass fill is sprayed between the rafters and is both fire and moisture resistant. It fits perfectly into tight spaces, so it also can be used to retrofit a poor insulating job and has an R-value of 4. While fiberglass cannot decay, it does require a vapor barrier to prevent water damage.

Cathedral Ceilings

• The only insulation recommended by This Old House for cathedral ceilings is foil-faced polyisocyanurate. These rigid sheets covered with foil act as both insulation and a radiant barrier. It is non-flammable and has an R-value of between 7 and 8. While it does not require a vapor barrier, it does require a wallboard covering.

Pipes

• Pipes running through roofs and attics are often neglected when it comes to insulation. This is a mistake that can cost homeowners large amounts of money should the pipes ever sweat. The best insulation for roof and attic pipes is by far rigid insulation. Rigid insulation is a board-like insulation form that companies custom mold to fit around pipes. It has a higher R-value for small spaces than most other forms of insulation and is typically covered with a radiant barrier to block even more heat.

Hot Climates

• For hot states such as Nevada and Arizona, radiant barriers offer the most insulation benefits hands-down. The barrier is designed to directly block heat and can be installed to either an attic's rafters or floor. Best of all, it is completely fire proof, will never settle and reduces a home's cooling costs by up to 30 percent.