Fiberglass insulation's properties mainly block conductive heat flow, the way in which heat travels through the materials used to construct your home. It also helps slow convective heat flow when you insulate your attic with the correct amount and type of insulation for your region. The measurement of its heat flow resistance is in its R-value. Fiberglass insulation with greater R-values offers better resistance against heat flow because it is denser. While fiberglass insulation reduces heat flow, it does not stop air movement.
The process to make fiberglass insulation is a proprietary one that starts with using recycled glass, sand, soda ash and other elements kept secret by the manufacturer. Heated in a massive oven until it reaches a specific temperature and molten state, it then goes into a cotton-candy-type unit that spins the molten glass into fibers. The fibers are laid onto a mat, where it is treated with preservatives and stabilizers. After moving through another oven, backing is attached to the mat for faced fiberglass. The insulating qualities of fiberglass come from the trapped air between the glass fibers and not the fibers themselves.
Fiberglass insulation R-values indicate the density of the insulation and the space it fits. Standard two-by-four framing accepts R-11, R-13 or R-15 insulation because they all generally are 3 1/2 inches thick. Walls built with larger studs can take insulation with a higher R-value such as R-19 or R-22. R-19 is 6 1/4 or 6 1/2 inches thick, while R-22 comes in 6 1/2- and 7 1/2-inch thicknesses depending on the manufacturer. Attics usually require a minimum of R-38 or two R-19 batts atop each other, but the part of the country in which you live could dictate higher R-values, such as R-60 depending on the weather. Fiberglass dimensions vary with the R-value.
When you compress fiberglass insulation into a space it was not designed to fit, you are throwing away your money. Compressing fiberglass insulation destroys its insulation qualities because you have squeezed the air out of the insulation. Shoving more insulation into the space is not the answer. For fiberglass insulation to work correctly, start at the top and gently set it into the space as you work down the batt. Insulation that has facing requires installation with the paper or foil facing the inside of the room. Before installing insulation, make certain it is sized to fit your needs and meets the requirements to provide an energy-efficient barrier to the home.
Vapor Diffusion Retarder
Because insulation does not resist airflow, when you add a moisture barrier or vapor diffusion retarder after installing insulation, you can significantly affect the energy-efficiency of your home -- even a well-insulated one. A diffusion retarder stops air and moisture movement. In conjunction with adding a vapor diffusion retarder to the exterior of your home before you install siding, add a retarder to crawlspace walls and underneath homes with a raised foundation.
- Lowe's: How Insulation Prevents Heat Transfer
- Energy.gov: Insulation
- CertainTeed: Fiberglass Insulation
- CertainTeed: Insulation Guide
- ICS Insulation: Building Insulation Product Reference Guide
- GreenBuildingAdvisor.com: Installing Fiberglass Right
- Energy.gov: Vapor Barriers or Vapor Diffusion Retarders
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