This specification covers the composition and physical properties for perlite thermal insulation board used principally above structural roof decks and as a base for built-up, modified, and elastomeric membrane roofing in building construction. Perlite thermal insulation board is classified as follows: type 1 - roof insulation board, and type 2 - roof cover/recover board. The basic material of the insulation board shall be perlite expanded by the application of heat to form glassy, cellular aggregates. The finished board may be either single-ply or multiple-ply. Perlite thermal insulation boards shall conform to the thermal resistance prescribed. The thermal resistance, compressive strength, tensile strength, flame speed classification, and water absorption shall be tested to meet the requirements prescribed.