- The thermal resistance of insulation materials is measured per inch of thickness. For example, the R-value of fiberglass insulation is 3.0 per inch. A 4-inch batt of fiberglass would have an R-value of 12 (since 3.0 x 4 = 12). An object's thermal resistance is a measure of its ability to slow the transfer of energy (heat and cold) from one side of the insulator to the other. The higher the R-value, the greater the effectiveness of the insulation.
- Mineral wool is similar to fiberglass. It is installed by blowing in the loose fill into the space. It is made with slag or rock spun into a wool. It is treated with oil to reduce dust and to bind it together. It is water-resistant, non-combustible, rot-resistant and inexpensive. It has an R-value of 3 to 4 per inch.
- Cellulose is made from shredded newspaper and chemically treated to resist fire, rot and fungus. It is also installed by blowing it in. Cellulose is denser and is a better air barrier than fiberglass. It will absorb water readily, which will permanently reduce its R-value because of compression. It has an R-value of 3.5 per inch.
- Foamed-in-place insulation provides a superior air barrier because it expands to fill all of the gaps. It is applied by spraying it into the space with a special gun. These materials are combustible and need to be covered with drywall to provide a fire barrier. They are typically more expensive to apply but can offer a R-value per inch of up to 6.
- Fiberglass is the most commonly used insulation type in modern construction. It is available in loose fill, batts and solid board applications. Its R-value is approximately 3 to 4 per inch. It is recommended that you wear gloves and a breathing mask when installing to avoid irritation to your skin and lungs. Blowing in loose fill fiberglass is the least expensive way to add insulation to your attic.
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