The purpose of insulation is holding heat in during the winter and keeping it out during the summer. Because of climate variations, homes in different regions of the country need different levels of insulation in the walls, ceilings, floors and windows. To find out the recommended R-value in your area, contact your local utility or local building department.
This chart shows how many inches of a certain type of insulation it takes to achieve a specified R-Value.
In the following chart, you'll see that R-30 requires 14.5 inches of vermiculite,
nearly 8.5 inches of fiberglass batt or only 5 inches of urethane foam. Such
comparisons are helpful in selecting insulation types because the type you can
use may be limited by the space available.