Heat inflow or outflow has important effects upon the occupants of a building. The use of insulation improves comfort conditions and savings in fuel. The materials commonly used for insulation may be classified as blanket, batt, loose-fill, reflective, and rigid. These materials are manufactured in a variety of forms and types, and their insulating values vary with the type of construction, kinds of construction materials used, and thickness of insulation. Figure 6-66 shows different types of insulation commonly used in construction.

Vapor barriers should be used to keep moisture from seeping through walls, floors, and ceiling materials. Among the effective vapor-barrier materials are asphalt laminated papers, aluminum foil, and plastic film. Most blanket and batt insulations (fig. 6-66) have paper-backed aluminum foil on one side to serve as a vapor

Figure 6-65.-Ceiling tile assembly: A. Nailing strip location; B. Stapling.

Figure 6-66.-Types of insulation: A. Blanket; B. Batt; C. Fill; D. Reflective (one type); E. Rigid.

Figure 6-68.-Inlet ventilators: A. Small insert ventilator; B. Slot ventilator.

barrier. Foil-backed gypsum lath or gyspum boards are also available and serve as excellent vapor barriers. Where other types of membrane vapor barriers were not installed during construction, several coats of paint do provide some protection. Aluminum primer and then several coats of flat wall or oil paint are effective in retarding vapor transmission.

Even where vapor barriers are used, condensation of moisture vapor may occur in the attic, in roof spaces, and in crawl spaces, if any, under the building or porch. In such spaces, VENTILATION is the most practical method of removing condensed or hot air that may other-wise facilitate decay to the structure. It is common practice to install ventilators, several types of which are shown in figures 6-67 and 6-68.