The Insulation

Once the mechanical rough-ins are complete, insulation will be installed in the wall cavities. Insulation is relatively new—few houses built before 1940 had what we today would recognize as insulation. But in our energy-conscious age, insu­lation is a given.

Thermal building insulation resists the flow of heat: During the heating season, less warm air escapes and, during hot weather, less overheated air enters through properly insulated ceilings, floors, and extertor walls. Most insulation is made of airy, diffuse materials full of dead air spaces because air is a poor conductor of heat.

KINDS OF INSULATION. There are three basic categories of insulation that may be used in your home.

Batts and blankets. Thick blankets or batts of fiberglass, "glass wool," or cotton insu­lation are common in new construction and in retrofitting old where the wall cavities are open and accessible. The insulation, which comes in thicknesses of 1 to 13 inches, is stapled between the studs in the walls or the joists or rafters in the ceiling or floor.

Loose fill. Cellulose (typically made of recycled paper products), fiberglass, cotton, or even perlite or vermiculite are used as loose fill insulation. That means they can be poured by hand or machine blown into ceiling cavities or, in instances where the interior wall surfaces have not been removed, between wall studs. The loose fills tend to flow readily into nooks and crannies. A variation of this is a mix of loose fill with a binder or glue that enables the material to be pumped in and, when the glue hard­ens, to hold its shape. Foams like polyicynene are installed in the same way

Rigid plastic boards. Typically of extruded or expanded polystyrene, polyisocyanu- rate, or fiberglass, rigid plastic boards are often used in new construction as exterior sheathing for walls or roof decks or interior masonry walls. Rigid insulation is avail­able in a variety of thicknesses, from Va inch up to 10 inches.