Polyiso roof insulation represents more than 55 percent of all insulation used in low-sloped roof construction.
The average thickness of insulation in roof applications is approximately 2 inches. Polyiso insulation has more R-value per inch of thickness than expanded- or extruded-polystyrene insulation. Two-inch thick polyiso offers 40 percent better thermal performance than polystyrene of the same thickness. Because it is thinner for the same R-value, the roofing contractor usually can obtain a number of economies including wood blocking thickness at perimeters and penetrations while obtaining the correct flashing height. This system also provides increased flexibility when designing tapered systems to drain water more efficiently from the roof.