Faced rigid board polyisocyanurate insulation is the most popular type of insulation used in low-slope roof systems in the U.S. However, the product's ASTM International standard is confusing and cumbersome, which often results in inadequate or improper specifications. If you are involved with specifying or installing polyisocyanurate insulation, you should be aware of these concerns.
The U.S. product standard for faced rigid board polyisocyanurate insulation is ASTM C1289, "Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board."
ASTM C1289 is divided into seven types identified as Types I through VII. Type I products are faced with aluminum foil and typically are used in wall sheathing applications. Type II products are faced with mat facers and typically are used in low-slope roof systems. Types III through VII products include composite-type polyisocyanurate boards laminated with perlite board, wood fiberboard, oriented strand board, wafer board or glass mat-faced gypsum board and often are used in roof systems.