Theory of Roof Insulation

Heat Flow

• Radiation, convection and conduction contribute to the flow of heat. Radiation is the transfer of heat through a space using electromagnetic energy, such as the heat you feel from the sun’s rays. Convection refers to the transfer of heat in the air by physically moving molecules, such as the heat that rises from steam. Conduction is the transfer of heat by means of kinetic energy, like when the handle of a frying pan feels hot even though only the bottom of the pan touches the burner.

Insulation Values

• Insulation is measured in R-values, which represent thermal resistance or the resistance to heat flow. The more R-values roof insulation contains, the better it slows the flow and transfer of heat. If different materials have the same R-value but vary in thickness or weight, they still have the ability to insulate equally as well. The U.S. Department of Energy states that you should base the type of insulation you use on the weather patterns in your geographic location and your power bill. The DOE provides insulation recommendations regarding roof insulation, which may have a higher R-value than local and state codes. R-values can go as high as R-50.

Types of Roof Insulation

• There are several types of insulation such as batts, rolls, loose fill and spray foam, but these may not be appropriate for a roof. The most common types of insulation for roofs include rigid foam insulation and reflective insulation. Rigid foam insulation, which has an R-value of R-4 to R-6.5 per inch of thickness, is good for roofs in areas that need high amounts of insulation. Reflective insulation helps reduce the flow of downward heat with the use of foil. Contractors generally place reflective insulation between roof rafters.

Cool Roof Coatings

• The use of cool roof coatings helps prevent heat loss in the winter and heat gain in the summer. The coating is white or has reflective properties that reflect sunlight and prevent the flow of heat into a home. The DOE states that this type of insulation comes in the form of a thick paint that offers protection against water damage, chemicals and ultra-violet light.