House Insulation & Vapor Barriers

Fiberglass

• The formula for making fiberglass insulation is a carefully guarded secret. Natural materials, including silica, soda ash and limestone, in a furnace at several thousand degrees, then extruded into long threads, laid down on a conveyor belt in a mat and heated again. Saint-Gobain, based in France, the worldwide leader in habitat and construction materials, licenses its fiberglass insulation technology to the biggest insulation manufacturers in the United States. Saint-Gobain’s own subsidiary CertainTeed, Owens Corning and the Johns Mansville Company manufacture 80 percent of the fiberglass insulation nationally all using similar processes. Saint Gobain, formidable in glass manufacturing of all types, has been in business since 1665, when it constructed the mirrors for the Hall of Mirrors in Versailles, France.

Insulation Types

• Other forms of insulation include mineral wool – slag and rock wool – and cellulose. Mineral wool is made from iron-ore blast furnace slag and produced in blankets or “batts.” Its loose-fill is often used in place of fiberglass. Cellulose consists of recycled wood fiber, paper and newsprint treated with a fire retardant; it's also made as loose fill. Other insulation types include cement block insulation and foam board. Insulation is categorized by the measure of its resistance to heat flow known as its R-value.

Vapor Barriers

• Vapor barriers reduce the flow of water vapor through the material into the home. The government’s Energy Savers website says that the term vapor barrier implies keeping all moisture out, when a better term would be “vapor diffusion retarder,” as vapor barriers allow the penetration of some moisture. After the house is built and the exterior structural material is on the house, such as oriented strand board, install the vapor barrier before adding the final siding. Install siding right after installing the vapor barrier, as continued exposure to the ultraviolet rays of the sun will cause the vapor barrier to loose its functionality. Many people forget this important step to sealing the energy envelope, because a vapor barrier is never seen once siding goes on.

Types of Vapor Diffusion Retarders

• Like insulation, different types of vapor diffusion retarders are available for use. These include “structural” vapor barriers such as rigid foam insulation, aluminum, reinforced plastics and stainless steel mechanically fastened to the exterior and joint-sealed. Polyethylene vapor membranes come in large rolls, unrolled onto the house and fastened with staples. Some contractors use paper-faced or aluminum-faced fiberglass roll insulation on the home's exterior before siding as well. A polyethylene vapor barrier requires exterior installation for above-grade walls in climates with 8,000 heating degree days or higher, according to the government’s Energy Savers website.