R21 insulation is approximately 5.5 inches thick. This type of insulation is often used in walls and provides a higher R-value compared to standard insulation options, contributing to improved energy efficiency and thermal comfort in residential and commercial buildings.
Insulation should face the living space, with the vapor barrier (the paper or foil backing) towards the interior to help control moisture.
Calculate the amount of insulation by dividing your attic's square footage by the coverage area of the insulation package you plan to purchase.