Insulation comes in many forms. Understanding the properties of each form will help you choose the best types for your home.
Loose-fill insulation (also called blown insulation) consists of loose fibers or granules made from cellulose (recycled newspaper), fiberglass (glass fibers), rock wool (fibers of molten rock or slag), recycled cotton, or other materials. Loose-fill insulation comes in bags and is usually blown into cavities or attics using special equipment, conforming to the space in which it is installed. Sometimes it is blown at relatively high density (dense-pack insulation) to increase resistance to air infiltration.
In existing homes, loose-fill insulation is commonly applied in attics, where it can be blown over existing insulation. It can also be blown into uninsulated wall cavities through access holes drilled from either the inside or the outside (and later plugged). If you are thinking about re-siding your home or refinishing the inside of exterior walls, this is a good time to consider adding loose-fill insulation. If you’re opening wall cavities or building new exterior walls, loose-fill insulation can be blown in, and a cover attached to the wall studs to hold it in place (this is called a blown-in blanket (BIB) system). In multistory houses, dense packing rim joists between floors is an excellent way to insulate and air seal an often overlooked area.
Loose-fill fibers can also be sprayed, mixed with water and sometimes adhesives, into open walls before drywall installation, or to cover irregularly shaped or hard-to-reach areas. This technique—called wet spray—is often used with cellulose. The insulation dries within a few days and, once dry, resists settling. Waiting for the insulation to dry before adding a vapor barrier to the wall can be inconvenient, however. Some newer processes (moist- or damp-spray) speed up drying time by using much less water. Some installers also use drying machines.
Batts and Blankets
Batts and blankets are flexible, bound insulation made from glass, rock wool, or cotton fibers. They come in rolls (blankets) or precut strips (batts). Both come in standard widths (16 or 24 inches) to fit between framing members.
Batts and blankets can fit under floors, in attics, and in unfinished walls. Both are available with or without a vapor-retarder facing. This facing is usually not fireproof, so it should not be used where it will be exposed to an open space, unprotected by drywall or other less flammable material.
Good installation is crucial. Avoid allowing batts or blankets to be compressed—as often happens around plumbing and electrical wiring or when squeezing thick batts into narrow cavities. This lowers the R-value. If batts sag within a wall cavity, the resulting gap will also lower the overall R-value, so secure them against gravity as needed. Batts or blankets that come with vapor-retarder facings must be placed in cavities with the vapor retarder in the proper orientation, which depends on your climate.
Rigid insulation is made from plastic foam or fiberglass, pressed or extruded into panels. Rigid insulation can provide air sealing when the seams are properly taped, and may also have some structural value when used as a continuous layer on exterior structural walls.
Rigid foam insulation is made from polyurethane, isocyanurate, or polystyrene. It is commonly used under exterior siding and in foundations. Since it has a high R-value, it is useful where you need a lot of insulation in cramped quarters—for example, in cathedral ceilings. Foam insulation must be covered with finishing material for fire safety, and is not termiteproof unless it’s treated or protected.
If you plan to replace your home’s siding, this is a great time to improve the wall insulation by applying an inch or more of rigid insulation to exterior walls before the new siding goes on. Such continuous insulation reduces the thermal bridge effect that occurs in framed walls.
If you’re building an addition, you might want to consider using structural insulated panels (SIPs) instead of traditional framing. SIPs consist of a foam core with structural sheathing glued to both sides. The insulation is usually expanded polystyrene (EPS) or polyurethane foam, which is impermeable to moisture.
If your addition includes a concrete wall, you might want to use rigid foam form blocks, known as insulating concrete forms (ICFs). These are generally made from EPS and are stacked so that their hollow centers are aligned. The cavities are then filled with concrete, and sometimes reinforcing bars, to create an insulated structural concrete wall.
Another technique uses all-in-one exterior insulation and finish systems (EIFS). These have a finish similar to stucco, and can be cut in various shapes and placed over standard wood framing. EIFS must be carefully installed according to the manufacturer’s specifications to avoid termites and moisture problems.
Foam-in-place (also called sprayed foam) materials are mixed and sprayed, or extruded, into wall or other cavities using special equipment. They provide air and moisture sealing as well as insulation. Their ability to fill very small cavities enhances their performance over batts and other cut-and-fit types of insulation. Foam-in-place insulation is also useful at rim joists.
These liquid foam insulations are made from magnesium silicate (cementitious foam), isocyanurate, or polyurethane. Urea-formaldehyde foam was used in the 1970s and early 1980s, but is no longer available for residential use due to its toxicity.