R-Value

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R-Value

(1) R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the insulation resists heat transfer. Many factors can affect the R-value of insulation, including the type of insulation, and the age of the insulation. To determine the R-value of the insulation in your house, first determine the type of insulation present, whether that insulation is new, and measure the depth of the insulation in inches. Look your insulation up on the table below, and multiply the R-value per inch by the number of inches present in your house.

(2) The thermal resistance of a glazing system. The R- value is the reciprocal of the U-value. The higher the R value, the less heat is transmitted throughout the glazing material.

(3) “R” is the measure of a substance’s resistance to heat flow. An “R” value is a number assigned to insulation; the higher the number, the better the insulation.

(4) A unit of measurement of resistance to heat flow in hr. ft2 ° F/BTU.in.

(5) Quantitative measure of resistance to heat flow or conductivity, the reciprocal of U-factor. The units for R-value are ft2 °F hr/Btu (English) or m2 °K hr/W (SI or metric). While many in the building community consider R-value to be the primary or paramount indicator of energy efficiency, it only deals conduction, one of three modes of heat flow, (the other two being convection and radiation). As an example of the context in to which R-value should be placed, 25% to 40% of a typical home's energy use can be attributed to air infiltration.

See R Value.