As will be discussed in the next chapter, energy or building codes will prescribe the insulation values of exterior walls. Research seems to indicate that a total wall R-value of R-19, using batts, blankets, blown-in insulation, or sheathings, is typically recommended. Cracks around windows and doors should be addressed, whereas loose insulation or foam should be used in spaces around the rough framing and around the heads, jambs, and sills. Insulated doors are available, some with a thermal resistance value of R-5.
Insulated window units have airspaces between double or triple panes of glass that slow heat loss. To be truly effective, the units actually should contain an inert gas in the airspace; however, such windows are a little more expensive.