Building a New House? What You Should Know about Insulation

If you are buying or building a new house, make sure that recommended energy-saving features are included. The Federal Trade Commission (FTC) home insulation rule requires the seller of a new home to provide information on the type, thickness, and R-value of the insulation that will be installed in each part of the house in every sales contract. Insulation contractors are required to give their customers similar information. Many state or local building codes include minimum requirements for home insulation. Be sure that your new home or home addition meets these building codes. Also, some government home financing programs require that the home be built to meet the Model Energy Code. You may wish to install insulation beyond the minimum specified in such codes, especially if those minimum levels are below those recommended in this fact sheet.

To keep initial selling prices competitive, many home builders offer standard (not optimal) levels of insulation, although additional insulation would be a good investment for the buyer. The Model Energy Code and other guidelines for new home construction are published by several organizations. Following these guidelines will provide you with a more energy efficient home. These guidelines also describe methods you can use during house design to compensate for energy lost through metal studs in the walls or a large amount of windows. You should find out if your builder constructs homes in accordance with these guidelines. It is almost always more economical to install the recommended levels of thermal insulation during initial construction rather than adding insulation later.

How Much and Where?

Figure 1 shows which building spaces should be insulated. Discuss the house plans with your builder, and make sure each of these spaces is insulated to the recommended R-values.

The homeowner could then check Table 1 to find several choices. Remember to buy the insulation based on this R-value, and to check the product label to determine the insulation's proper thickness. Specialty insulation products are available to provide higher insulation values in confined spaces in new homes, such as in wall cavities and cathedral ceilings.

When both insulative sheathing and cavity insulation are specified for walls, it's important to use them together as a system. Also, these recommendations assume that the insulative sheathing will be placed outside a wood sheathing product. If you choose to replace the wood sheathing with a combination of insulative sheathing and necessary bracing, you should choose sheathing with a slightly higher R-value.

The band joists, or outside edges of frame floors, should be insulated while the house is under construction. Foundation insulation options for new construction are broader than for existing homes. The builder may, for example, choose to insulate the exterior of a basement or crawlspace wall. You should discuss termite inspection and control options with your builder when choosing your foundation insulation method. Special sill plate (the joint between the top of the foundation and the bottom of the house frame) mineral fiber sealing products are designed to reduce air leaks if installed during the initial house construction. Spray polyurethane foam insulation can be applied to a home under construction and will not only insulate, but will also reduce air leakage in the building envelope. This foam insulation, along with other flammable insulations or insulation facings must be covered or otherwise protected to meet fire codes.

Design Options

Some new homes are built using metal frames instead of wood. When you insulate a metal-framed building, it is important to recognize that much more heat flows through metal studs and joists than through pieces of wood. Because of this difference, placing insulation between the wall studs, or between attic or floor joists, doesn't work as well for metal-framed houses as it does for wood-framed houses. If your walls have metal frames, you will probably need to place continuous insulative sheathing over the outside of the wall frame, between the metal framing pieces and your exterior siding. (Note that this insulative sheathing cannot take the place of plywood or other seismic bracing.) If your attic has metal joists, you may want to place rigid foam insulation between the joists and the ceiling drywall. It's important to recognize that even if you install the recommended level of insulation in a metal frame building, you will not necessarily get thermal performance as good as you would get from a wood structure with its recommended level. That's because the insulation R-values given in this fact sheet were chosen based on an economic evaluation of life-cycle costs to the consumer, not to meet an arbitrary energy conservation target.

Insulating concrete forms can be used to construct walls for new homes. These special concrete walls come in a variety of configurations and can provide additional thermal mass to your home to help reduce the effect of outdoor temperature swings. The Insulating Concrete Form Association can give you more information about insulating concrete walls.

Structural insulated panels can also be used to construct a house. These panels sandwich plastic foam insulation between two layers of a wood product, thus eliminating the need for structural wood framing members. This system can reduce air leaks into and out of the structure and therefore may offer improved thermal performance compared to stick-built walls. The Structural Insulated Panel Association is listed at the end of this fact sheet, and they can give you more information about structural insulated panels.

Some homes are built with an External Insulation Finish System (EIFS) that gives a stucco-like appearance. There is some controversy right now about whether or not these homes are likely to experience moisture problems. You should discuss this possibility with your builder and your insurance agent if you are considering this type of building.