Insulation is one of those building products that you never see, because it is usually covered up by something else. But if you don't have enough, or if it is installed incorrectly, you're wasting energy and paying more for heating and cooling than is necessary.
There are a number of insulation products you can use to prevent energy loss. However, it is important to realize that insulation is only one part of a two-prong approach to energy efficiency. The other arm of the plan involves sealing all of the holes, cracks or openings caused by pipes, wires, chimneys or anything that creates an opening in a wall, ceiling, or most importantly, attic floor.
These openings allow interior air to escape to the unconditioned (not heated or cooled) space that surrounds your home. The sealing process is called "air sealing," and requires silicone caulk and expanding foam that comes in a can. It isn't exciting work, and while easy, it requires attention to detail. It is extremely important because the openings are escape routes for heated and cooled air and because many insulation products do not stop moving air. If you plan on insulating, be sure to attend to air sealing as well.
Where to Insulate
Basically, insulation should be placed in any area that separates your heated and cooled living spaces from areas that are not heated and cooled. These areas include:
Walls between the living area and an attached garage
Floors over unheated basements
Floors over crawl spaces
The effectiveness of insulation is measured by its R-value - "R" stands for resistance to heat flow. The higher the R-value, the better. It is important to match the insulation to the application as well. For example, fiberglass insulation has an R-value of about 2.8 to four per inch. Some foam panels have R-values of seven or eight. But you can easily find fiberglass batts or blankets that are 12 inches thick and designed for use as attic insulation, providing over an R-40. Standard foam panels only come in one-half to two inch thicknesses.
Some products are easier to install than others. Fiberglass batts simply roll into place. They are manufactured to fit snugly between ceiling joists and wall studs. When installing any insulation, it is important that the product be placed flat against the surface you are insulating. Any air space under the insulation or gaps around the edges will limit the effectiveness of the product.
Here's a look at some common insulation products:
Type of Insulation
R-Value per Inch
Where It’s Installed
(Available in batts, blankets and as a loose fill material) 2.8 to 4
Open wall stud cavities
Floors over unheated spaces
Batts and blankets are DIY projects
Loose fill is a professional installation
Compressing the insulation or getting it wet reduces R-value
Cellulose 3 to 3.7
Closed wall cavities
Cellulose is ground- up paper treated with fire retardants
Blown-in with special equipment
Can be poured in place
Even distribution is necessary for effectiveness
Polystyrene: 4 to 5
Polyisocyanurate / polyurethane: 6 to 8
Interior basement walls
Interior applications must be covered with drywall for fire safety
Used for air sealing large openings
Some types are used under exterior siding to enhance the R value of the wall and prevent heat transfer through framing members
Open-cell: 3.6 to 4.3
Closed-cell: 5.6 to 6.8
Open and enclosed wall cavities
Between rafters on cathedral ceilings
Hard to reach areas
Irregularly shaped areas
Requires special application equipment
Closed-cell material is denser and acts as a vapor barrier
Both act as an air barrier
Use this chart as a reference point when insulating your home. Proper insulation will help lower your energy bills and keep your home at a comfortable temperature.
Fran Donegan is a DIY-for-the-home authority and writes on energy-saving tips for The Home Depot. Fran’s insulation tips are geared to provide you with numerous options for your home during the winter months. To research a variety of insulation types, you can visit the Home Depot website here.