Types of Insulation Materials
There is no mystery about insulation. Each of the materials that make up your house has some insulative value. But their effectiveness varies greatly. A 1-inch blanket of insulation has the same insulative value as 3 1/2 inches of pine planking, 22 inches of common brick, 40 inches of concrete, or 54 inches of stone. There is actually a measurement for the heat conductivity of combined building materials -it's called a "U-value"- but the calculations required are very complex. It's better to stick to R-values.
As mentioned earlier, air is a good insulator when confined to a small space or to cells inside a porous material. Of course, dense materials such as stone have few, if any, air spaces. On the other hand, fibrous or porous materials contain plenty of air. These materials are the most common types of insulation. They break up the air space between exterior and interior house walls, floors, and ceilings.
Where heat gain or loss through radiation is significant, foil is used to reflect the heat back toward its source. Most commonly, it is provided as a facing on blanket-type fibrous insulation (it serves double duty as a vapor barrier).
In some cases, foil is a backing on gypsum wallboard. And in some areas, foil alone is used as insulation.
Insulation is manufactured from several materials, all of them highly porous. They include fibers or granules of glass, mineral, and organic materials, as well as some types of plastics. A good insulation product is resistant to vermin and moisture and to any change that would hinder its effectiveness. And it is fireproof when properly applied.
These R-values should not be used for estimating thickness. The actual values for a given insulation change with temperature and, in the case of some materials, depend on the manufacturing process used.
Of course, insulative value isn't the only factor to consider when choosing a material. Cost, method of installation, and general traits all count-and these factors vary greatly. Here is a brief description of each type.
Vermiculite and perlite
These are not as commonly available as other types of insulation.
Vermiculite is made from expanded mica. It is packaged in loose-fill granules (the smallest available) that are hand poured into attics and hard-to-reach spots. Though it is relatively easy to install, vermiculite tends to absorb moisture, becoming mushy and decreasing its already-low insulative value. Perlite, a type of volcanic rock, is comparable to vermiculite but has a slightly higher R-value.
Fiberglass and rock wool, the two products grouped under this heading, make up 90 percent of homeowner-installed insulation. Fiberglass is made from glass fiber. Rock wool, spun from molten slag rock, has a slightly higher R-value than fiberglass.
Mineral wool is available in several forms: packed into flexible blankets and batts, shredded for hand pouring or machine blowing, and compressed into rigid boards.
Though both fiberglass and rock wool are irritating to skin, rock wool is the less bothersome of the two.
A type of plastic, polystyrene is a rigid-board material. Though it dents easily and is highly combustible, its weather and moisture resistance make it excellent for below-grade or exterior-wall applications. Used indoors, it is a fire hazard unless covered by gypsum wallboard. In some cases, polystyrene should be installed by a qualified contractor.
Made from recycled paper products, cellulose is a shredded insulation that is normally machine blown into unfinished attics by a contractor or by a homeowner using a dealer loaned machine.
Because of its fine consistency, cellulose can also be blown into walls that are covered on both sides-but this should be done only by a qualified insulation contractor. Even when a contractor performs the work, the coverage may be somewhat incomplete.
If you can't get a machine for blowing cellulose into an attic, you can spread it by hand. Though it is not irritating to skin, cellulose is quite dusty. It is flammable unless treated, so be sure the bags you buy are clearly marked as meeting federal specifications. Also make sure the material has been treated for rodent resistance.
Because cellulose fibers have natural air cells inside them, cellulose insulation has relatively high R-values.
Though quite expensive, urea formaldehyde is excellent for insulating walls finished on both sides. It fills wall cavities totally and, once inside, creates its own vapor barrier. Because the equipment and procedures are specialized, a contractor must install it. It has excellent resistance to fire and has high R-values. On the negative side, it can cause a slight odor that lingers for a week or two, and the R-values may tend to decrease slightly with time. For more about this material.
Though urethane has the highest R-values of all insulations, it gives off poisonous gases when ignited. It comes in rigid-board panels or as a foam like urea-formaldehyde. If foamed in place by a contractor, it completely fills the spaces where it is installed and it creates its own vapor barrier. But because of the toxic gases it may give off, urethane is not recommended for use in walls.
In some localities, urethane foam is applied to roof surfaces by contractors. Like rigid boards, this relatively new insulating method can be an excellent way to insulate houses with no attics.