R-Value: Material differences

February 01, 2001 |

In colder climates, roof insulation slows the loss of heat through the roof, which is the part of a building that is most vulnerable to heat loss because heat rises. In warmer climates, roof insulation can greatly reduce the effects of solar energy, acting as a barrier between the heat of the sun and an air-conditioned building. In both instances, quality insulation can pay for itself many times over in energy savings from reduced heating and cooling costs.

In addition to design attributes, durability and initial cost, energy performance (see table) is the major consideration when specifying roof insulation. Choices for specifiers include chemically produced products such as polyisocyanurates, expanded or extruded polystyrenes, polyurethanes and ureaformaldehyde. Naturally occurring materials such as mineral wool and cellulose are also common choices.

R-Value (energy performance) comparison

Insulation type R-value/1"

Polyisocyanurate and polyurethane


Extruded polystyrene


Expanded polystyrene


Mineral fiber


Cellular glass


Source: Society of the Plastics Industry

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