Fiberglass and cellulose insulation typical come in batt or blown form. Blown insulation is also known as loose fill. Batt insulation is processed in rolls and comes in varying lengths, generally 4 to 8 feet. It works well for use in insulating floors, ceilings and walls. All insulation material is given an R value, which is a rating of its insulating factor.
Batt insulation is processed in rolls of varying thickness. Generally, they are found in thicknesses of 6 to 12 inches. Batt insulation may be fiberglass, cellulose or (less commonly) wool. Batts are designed to fit snuggly inside wall, ceiling or floor cavities and are therefore made to a width of 16 to 24 inches. Most often, batts are packaged in rolls that are compressed and expand when unraveled and placed. A typical roll of batt insulation is 8 feet long.
The purpose of batt insulation is to insulate the home to retain heat and cold inside and keep outside heat and cold from penetrating the home. People regularly assume that insulation serves the purpose of keeping the home warm, which it does, but it also serves to keep a house cool during summer months. An additional benefit of insulation, batt or blown, is that it helps to deaden sound from outside the home.
The R value of a particular roll of batt insulation will be noted on the package. The R value is a measure of the insulating factor of the material. Without getting into very specific scientific formulas, the R value is a ratio of temperature difference across an insulator. The higher the R value the better the insulating factor. Although it varies by material and product manufacturing, the R value for 1 inch of batt insulation is about 3 to 4. In the northern hemisphere, a typical recommendation for a home is to have an attic insulation R value of 49 (or about 17 inches of insulation). An R value of 19 is a typical value for a 6-inch-thick batt. When insulating an attic, you would want to use three layers of batt insulation to meet the recommendation. Walls and flooring have different recommendations, and a single batt usually meets that requirement.
Batt insulation is generally the least expensive insulating option, but can also require the most work to be installed correctly. It is important to follow manufacturer installation instructs so that the batts deliver the most energy efficiency and to avoid seams that will lower the insulating factor of the product. Many older homes are lacking in sufficient insulation. This is due, primarily, to lower building standards at the time of construction.
Moisture leaks and air leaks will reduce the effective R value of insulation. R values are tested in controlled environments, and it is safe to assume that the rated R value is slightly higher than the effective R value.
Cellulose insulation is becoming much less common than fiberglass insulation. Fiberglass insulation meets higher fire safety ratings, is less prone to holding moisture and is less likely to retain mildew or mold.
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