Reflective

Figure 5-27.—Types of insulation. wool, wood fibers, shredded redwood bark cork wood pulp products, vermiculite, sawdust, and shavings. Fill insulation is suited for use between first-floor ceiling joists in unheated attics. It is also used in sidewalls of existing houses that were not insulated during construction. Where no vapor barrier was installed during construction, suitable paint coatings, as described later in this chapter, should be used for vapor barriers when blow insulation is added to an existing house. Reflective Most materials have the property of reflecting radiant heat, and some materials have this property to a very high degree. Materials high in reflective properties include aluminum foil, copper, and paper products coated with a reflective oxide. Such materials can be used in enclosed stud spaces, attics, and similar locations to retard heat transfer by radiation. Reflective insulation is effective only where the reflective surface faces an air space at least 3/4 inch deep. Where this surface contacts another material, the reflective properties are lost and the material has little or no insulating value. Proper installation is the key to obtaining the best results from the reflective insulation. Reflective insulation is equally effective whether the reflective surface faces the warm or cold side. Reflective insulation used in conjunction with foil-backed gypsum drywall makes an excellent vapor barrier. The type of reflective insulation shown in figure 5-27, view D, includes a reflective surface. When properly installed, it provides an airspace between other surfaces. Rigid Rigid insulation (fig. 5-27, view E) is usually a fiberboard material manufactured in sheet form. It is made from processed wood, sugar cane, or other vegetable products. Structural insulating boards, in densities ranging from 15 to 31 pounds per cubic foot, are fabricated as building boards, roof decking, sheathing, and wallboard. Although these boards have moderately good insulating properties, their primary purpose is structural. Roof insulation is nonstructural and serves mainly to provide thermal resistance to heat flow in roofs. It is called slab or block insulation and is manufactured in rigid units 1/2 inch to 3 inches thick and usually 2- by 4-foot sizes. In building construction, perhaps the most common forms of rigid insulation are sheathing and decorative covering in sheet or in tile squares. Sheathing board is made in thicknesses of 1/2 and 25/32 inch. It is coated or impregnated with an asphalt compound to provide water resistance. Sheets are made in 2- by 8-foot sizes for horizontal application and 4- by 8-foot (or longer) sizes for vertical application. Miscellaneous Some insulations are not easily classified, such a insulation blankets made up of multiple layers of corrugated paper. Other types, such as lightweight vermiculite and perlite aggregates, are sometimes used in plaster as a means of reducing heat transmission. Other materials in this category are foamed-in-place insulations, including sprayed and plastic foam types. Sprayed insulation is usually inorganic fibrous material blown against a clean surface that has been primed with an adhesive coating. It is often left exposed for acoustical as well as insulating properties. Expanded polystyrene and urethane plastic forms can be molded or foamed in place. Urethane insulation can also be applied by spraying. Polystyrene and urethane in board form can be obtained in thicknesses from 1/2 to 2 inches. 5-21