How Thick Is R13 Insulation?

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Fiberglass batt insulation is easy to obtain and install.

The US Environmental Protection Agency recommends floor insulation values of R13 to R19 in warm parts of the United States where winter temperatures never become extremely cool. In other areas of the country, homeowners need more insulation to keep their homes from losing significant heat during the winter. Most homes are under-insulated, and many more have had their insulation settle over the years. Learning the R-value of the most common types of insulation can help homeowners decide how much to add to their homes' floors, attics and walls.

Blanket Insulation

The most common and easily obtainable type of insulation, blanket insulation, is usually made from fiberglass or mineral wool. Some blanket insulation is also made from plastic, wool or cotton. Standard fiberglass batts have an R-value between 2.9 and 3.8 per inch of thickness, while high-performance batts offer values between R3.7 and R4.3. According to the US Department of Energy, the average 3-5/8 inch fiberglass batt offers insulation values around R13.

Foam Board

Made from polyurethane, polystyrene or polyisocyuranate, rigid foam board insulation is also sometimes called beadboard. Polystyrene foam board offers insulation values between R3.8 and R5 per inch, requiring 2-1/2 to 3-1/2 inches to achieve R13. Polyurethane and polyisocyuranate offer higher R-values, between R5.6 and R8 per inch. Use between 1-5/8 and 2-1/3 inches of this material to reach R13.

Loose Fill

Loose fill insulation is made up of many small particles. It can be made from chopped fiberglass, rock wool or cellulose. Fiberglass loose fill insulation offers the lowest insulation value, at about R2.2 to R2.7 per inch. Rock wool offers R3 to R3.3, while cellulose provides R3.2 to R3.8. Depending on the type and density of the insulation used, homeowners need between 3-1/2 and 6 inches of this material to provide R13 insulation values.

Spray Insulation

Spray foam insulation can fill very small cavities, allowing it to be much more effective than batt or foam board insulation, especially in retrofit situations. Types include cementitious foam, polyurethane foam, phenolic foam and polyisocyuranate. Cementitious foam contains cement and provides about R-3.9 per inch and requires 3-1/3 inches to provide R-13 insulation values. Polyurethane foam offers initial values up to R9 per inch, but its insulation quality drops over time to about R7. Use 1-7/8 inch of this foam to provide R-13. Phenolic foam offers R4.8, and requires about 2-3/4 inches to reach R13. Phenolic foam can shrink up to 2 percent after installation. Polyisocyuranate, a type of thermosetting plastic foam, provides R5.6 to R8 per inch. Use 1-5/8 to 2-1/3 of this foam to achieve R13.


G.D. Palmer

G.D. Palmer is a freelance writer and illustrator living in Milwaukee, Wis. She has been producing print and Web content for various organizations since 1998 and has been freelancing full-time since 2007. Palmer holds a Bachelor of Arts degree in writing and studio art from Beloit College in Beloit, Wis.