Learn the Basics About Home Insulation
A carefully considered insulation strategy that considers air sealing and ventilation can improve your home's energy efficiency, which reduces your utility bills. There are many kinds of insulation, and choosing the right one for a new home or remodeling project requires a carefully considered strategy.
Three critical elements of that strategy are:
- the type of insulation material;
- where it's installed;
- how much is needed.
If you're having a new home built, be sure to talk to your builder about these three elements so that you can be assured the insulation strategy will contribute to a comfortable, efficient home.
How Much Insulation to Use and Where To Install It
Local building codes spell out the answers to these questions. At a minimum, insulation is placed in the floor of an unfinished attic, in the exterior walls and in the wall between the garage and the living space. It also may be installed over wall sheathing, which is a material placed between the exterior wall and the cladding material (the brick, siding or stucco on the outside of a house). In some regions, local building codes require the foundation walls and slab to be insulated, too.
What Type of Insulation to Use
The builder should choose the insulation type based on the design of your home and your climate zone. A good resource for more information about choosing insulation is the U.S. Department of Energy website.
The following is a guide on what type of insulation is typically installed and in which parts of the house. This varies based on the climate and the individual characteristics of the house.
- Exterior Walls -- All building codes require insulation in the exterior walls between the wood studs that make up the frame of the walls. Of the many types available, fiberglass batt insulation is used most often. Fiberglass is an excellent insulator, and is very resistant to fire. Batt insulation is a type of insulation made of loosely matted fibers fashioned into a blanket-like form.
- Attic -- Most building codes also require insulation in the attic. Blown-in dry cellulose insulation is commonly used in this area of the home. It simply is blown-in to the depth required to meet the R-value specified by local code. Dry cellulose insulation is made from recycled, shredded newspaper, which has been chemically treated to be fire-resistant.
Blown-in insulation refers to loose insulation made of fiberglass, cellulose or foam that is literally blown into place with hose-type equipment. Fiberglass and cellulose remain loose after they've been installed. Spray foam solidifies once it's been applied.
- Wall Sheathing -- Rigid foam sheathing can be used to add thermal resistance to the exterior walls. Rigid foam sheathing often is used with a material that provides wall strength -- such as plywood.
- Foundation Walls -- In some areas, building codes require foundation walls to be insulated. To meet code, rigid fiberglass can be applied to the exterior of the foundation walls. For maximum benefit, foundation insulation is run from the wall sheathing to the bottom of the foundation wall.
- Slab -- In a slab-on-grade foundation, where the bottom of the house sits directly on the ground and doesn't have a basement space, codes often require the slab to be insulated. The preferred method is to extend rigid foam board from the top of the slab to two feet below the bottom of the slab. An additional two feet should angle out away from the vertical piece, as shown in this image. Insulating this way helps to keep the soil surrounding the slab warmer, thus keeping the slab itself warmer.
Remember, talk to your builder when your home is still in the planning stage to find out about the strategy being used to insulate your home, including the type of insulation material, where it's installed, and how much is needed.