R30 Insulation Thickness
R-value is based on the material used and the thickness of the material. 13 inches of fiberglass can be rated at R-30, while 13 inches of cellulose might be as high as R-45. R-value is lost when insulation is compressed – 13 inches of insulation that is rated at R-30 will lose some of its R-value if it has been compressed and shoved into a space that’s only 10 inches. Insulation basically works by trapping air so it can’t conduct heat. The air can be trapped between layers of fiberglass or cellulose materials or within foams. Compression reduces the amount of space to trap the air. Damp or moist air will reduce the effectiveness of insulating material.
The form of insulation most familiar to people is the batt – pre-cut into 4 foot or 8 foot lengths – or rolls up to 64 feet long. These are made of fiberglass or rock wool and are spun together much like cotton candy. They are flexible and come in widths -15 inch and 23 inch – that fit in standard spacing of wall studs and attic joists. In areas with non-standard joist spacing – near windows or doors – or where there are obstructions in walls – wires, pipes or electric outlets – the insulation had to be trimmed to fit. All space between joists has to be filled for the insulation to be effective. Batts may be installed by the homeowner and are available with or without vapor blocking facings. 9 inches of fiberglass batts is R-30.
Blown-in loose fill insulation is usually installed by professionals. Blowers are used to get the material into otherwise inaccessible spaces or areas where blanket insulation would not work. The loose fill materials will settle over time, so should appear deeper when first installed. 12 inches of fiberglass loose fill or 8 1/8 inches of cellulose loose fill equals R-30.
Rigid insulation is available in molded pipe coverings and board-like forms. Made from fibrous materials or plastic foams, rigid insulation is often used for foundations and as wall sheathing. 6 inches of rigid polystyrene board or 5 inches of rigid polyurethane board is rated at R-30.
Denser fiberglass insulation can give an R-30 value with less thickness. Rigid insulation gives the highest R-value for the thickness, but isn’t as flexible as fiberglass batts. Loose fill can have the lowest price for the material, but has the added cost of professional installation. Generally, The Cost of Denser Insulation is usually higher.
When you look at insulation you run into the term R-value. This term is used in the building and construction industries to tell the user the unit thermal resistance. That means how fast heat can transfer through the material. There’s a formula for finding the R-value available if you are interested, but most people are satisfied with the ratings for R-value that is on the package. Just keep in mind that R-value is a lot like MPG ratings – there can be a difference based on your usage. MPG ratings don’t mean much if you have a heavy foot on the gas pedal; R-value ratings will be dependent on the insulation being used as the manufacturer suggests. When a material is evaluated for R-value it is under certain conditions. These should be the same conditions under which it will be used.