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of Home Improvements

*Common Types of Insulation*

Commercial Insulations:

There is a bewildering array of insulations on the market, each product promoted by its manufacturer as the best. Each may, in fact, be best for a particular application but certainly not for all. The smart homeowner or builder will use several different types of insulation in order to achieve optimum thermal performance. Price and R-value are just two of the characteristics with which we should be concerned.

Fiberglass Blanket & Batt

This is probably the product that most homeowners think of when insulating their home.

Fiberglass blankets in long rolls and fiberglass batts in 4-foot lengths are both available in 15- and 23-inch widths, the perfect sizes to fit between joists, studs and rafters with standard 16- and 24-inch on-center spacings. In this bound form, the fiberglass is less likely to settle and so is perfect for insulating regular framing cavities.
Fiberglass insulation manufacturers have apparently (and unfortunately, to my mind) made a marketing decision to promote the blankets and batts in low-density versions with a rather moderate R-value of 3.2 per inch. Compressing thicker batts into framing cavities is worthwhile: while the total batt R-value goes down, R-value per inch and R-value of the fixed-cavity thickness goes up.
Strong points include low cost, ease of installation and wide availability. A weak point is the difficulty of filling irregular spaces. The best applications are between studs and rafters.

Long-Fiber Blown Fiberglass

Long- Fiber blown fiberglass is essentially silica, or sand, that has been melted and spun into fibers. The fibers are coated after cooling with a colored resin and gathered into blankets of varying density, depending on the desired R-value and application.Blown fiberglass is chopped into small clumps with a density of 0.6 pounds per cubic foot. The glass fibers are extraordinarily resilient and resist settling once their settled density has been reached. Therefore, when installed at the proper density, blown insulation does not settle in walls and leave empty heat-convection channels. Although the binding resin is combustible, the amount of it present is small enough for the overall product to be considered noncombustible. Strong points include cost per R-value, inertness and ability to fill irregular spaces. Its weakest point is low R-value per inch. The best application is on an open attic floor.

Sprayed Short-Fiber Fiberglass

Sprayed short - fiberglass insulation differs from long-fiber fiberglass in size and length of fibers, and installed density. The fibers and air spaces are smaller, resulting in a higher R-value per inch than the long-fiber version. More than twice the amount of material is required, however, leading to a price that is also more than double. Since the cost of material is usually a small component in the life-cycle cost of insulating.

Cellulose Insulation

Cellulose insulation is a loose, fluffy, fibrous material intended for blowing into cavities. It is generally made by finely shredding old newspapers. (Some claim the finest to be derived from the New York Times, although I believe that's purely a case of elitism.)
Cellulose insulation is not particularly resilient and must be installed at high density to avoid long-term settling. Minor settling is not very important in an open attic, where R-value is roughly proportional to thickness. Due to the thermal short-circuiting effect of air gaps, however, settling in wall cavities leads to significant loss of R-value. Unlike fiberglass, cellulose insulation is flammable, so it is treated with a flame retardant. It is important to keep cellulose dry, because saturating the fibers results in a permanent reduction in thickness and R-factor, and a possible loss of fire retardant.
Strong points are low cost, R-value per inch and ability to fill irregular spaces. Weak points are possible settling in walls, susceptibility to water damage, and possible corrosion of pipes and wiring by chemicals. The best application is, once again, on an open attic floor.

Perlite

Perlite is a naturally occurring volcanic mineral containing up to 5 percent water. When the mineral is crushed and then heated rapidly to its melting point, the trapped water turns to steam and blows minute glass bubbles. These highly insulating trapped air cells can be loose-poured, fused into a rigid board, or substituted for sand and gravel in insulating concrete.
Strong points of Perlite include inertness, non-combustibility and ability to flow into irregular spaces. Weak points include high cost and settling in wall cavities. The best applications are in filling irregular voids between attic fiberglass batts and insulating concrete.
The single strong point of molded polystyrene is the lowest cost per R-value of the foams. Weak points include fragility, low R-value per inch (compared with other foams), and the requirement to cover with a 15-minute fire-rated material in interior applications. The best application is as the core of large gypsum drywall/foam-sheathing panels, which are used to cover the roofs and walls of post-and-beam structures.

Polyicynene (Icynene)

Polyicynene is a modified open-cell urethane foam that uses water and carbon dioxide instead of ozone-depleting fluorocarbon blowing agents. It is applied either by spray gun to exposed framing cavities or by pouring a slightly different formulation into existing closed
cavities. Its R-value of 3.6 per inch is about the same as those of blown fiberglass and blown short fiber fiberglass, but significantly less than that of the more expensive urethane foams.
Polyicynene expands to fill framing cavities and adheres to surfaces, so it virtually eliminates air leakage. It is not vapor-impermeable, but its air impermeability prevents significant moisture buildup in wall cavities.

The advantage of polyicynene is its combination of relatively high R-value and air sealing. Its weak point is that it can be installed only by a licensed contractor, with resulting high cost. The best application is in sealing and insulating difficult areas, such as box sills.

Reflective Foils

Reflective aluminum-foil insulations are chameleons, defying the convention of a simple R-value per inch. The polished aluminum foil in most commercial reflective insulations has a reflectivity of about 95 percent, meaning only 5 percent of the normal amount of radiation gets through. A Thermos bottle uses the same principle, coating the inside surfaces of an vacuum bottle, reducing all three mechanisms (conduction, convection and radiation) to near zero. The fly in the ointment is that, except when used in space, the cavities in foil insulations are not evacuated, so we still have conduction and convection to deal with.

One must consider the physics when applying reflective foil insulations. They can be very effective in floors over unheated areas in cold climates. They are even more effective in blocking heat from the roof in cooling regions. But they are, by themselves, a poor choice for northern roofs.

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