"R-value" signifies the ability of a material to resist heat flow. The higher the R-value, the greater the heat flow resistance. For instance, it's more difficult for heat to pass through R-19 insulation than it is to pass through R-11 insulation.

Some materials are naturally better insulators than others. For example, a six-inch batt of fiberglass insulation has an R-value of 19, while an eight-inch concrete block has an R-value of 1.04. Glass, like concrete block, also has little resistance to heat – a single pane of glass has an R-value of 1.13.

The following chart shows average R-values per inch of common insulating materials. Using this chart, you can determine the R-value of a particular amount of insulation from its thickness. For example, 8.5 inches of loose-fill mineral fiber insulation equals R-19. Because R-values per inch vary greatly between different insulating materials, always rate insulation by its R-value and not by inches.

NOTE: Styrene and urethane foams may present smoke- and flame-spread problems if improperly used. Look for UL approval for cellulose. Untreated cellulose is highly flammable.

* R-values from the ASHRAE Fundamentals Handbook. The values given are average R-values. If needed, ask insulation manufacturers for the R-values of insulating materials not listed above.

The table below lists R-values for commonly available thicknesses of residential ceiling, wall and floor insulation:

Progress Energy's minimum recommendations for house insulation:

• In Florida:
  • Ceiling: R-19 to R-30
  • Wall: R-11 in frame walls, R-5 in CBS walls
  • Floor: R-11 in floors (suspended frame only)