If you build an energy efficient new home, you can improve your energy efficiency substantially by increasing the R-value of your home's wall insulation.
The R-value of a wall is a measurement of the its thermal resistance. Many homes are still built using the traditional standard of 2-by-4 walls and a R-11 fiberglass batt insulation. But energy experts don't consider this old standard to be adequate. Insulation dealers now sell enhanced batts for 2-by-4 walls that are rated either as R-13 or R-15. An even higher insulation level can be achieved by building a 2-by-6 wood wall, and using either the standard 5.5-inch fiberglass batt, rated at R-19, or enhanced batts rated at R-21.
It is also important to recognize the difference between the R-value of the wall insulation itself and the R-value of the whole wall assembly. The R-value of the whole wall is an average of the insulation and the framing lumber. Since the framing lumber is a poor insulator and occupies 12 to 25 percent of the wall's surface area, it creates cold spots in your home's thermal boundary.
Whenever possible, wood framing should occupy the minimum surface area of a home's wall. Here are a few common ways to reduce the wood content of an exterior wall.
Wood walls should be framed with 2-by-6 studs spaced 24 inches, rather than 16 inches, apart.
Wall corners, top plates, and intersections with interior walls should have as much insulation and as little wood as possible while still meeting structural codes.
Headers above doors and windows should be filled with foam insulation.
- Insulated foam sheathing (1 to 4 inches) should be installed as an exterior cladding underneath the siding to reduce the flow of heat through wall studs.
Structural insulated panels (SIPs) provide another solution. They are a manufactured sandwich of wafer board and white polystyrene foam. Their installation includes little framing lumber, so the whole-wall R-value is considerably better than wood-frame walls of the same thickness.
Insulated concrete forms are another energy efficient option in which concrete is poured into hollow foam blocks that are stacked together to form the wall. The wall exterior is usually covered with stucco or a masonry veneer of brick. These wall systems can reduce a home's energy consumption substantially.
The Homeowners Handbook to Energy Efficiency contains more information on insulation types and installation.