THERMAXTM brand insulation is a polyisocyanurate rigid board insulation with an R-value of 6.5 per inch. This product has FM 4880 class 1 wall and ceiling approval for fire exposure and can be left exposed in both the wall and ceiling providing a nice aesthetically pleasing look to the interior as well as increasing energy efficiency.
The Dow Chemical Company produces THERMAXTM Sheathing and THERMAX Insulation/Finish Boards, including White Finish (formerly AgTherm), Metal Building Board, Light Duty, Heavy Duty and Heavy Duty Plus, all are manufactured to meet the following specifications. Compliance to ASTM C-1289-06 "Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board", Type I, Class 2 and Federal Specification HH-I-1972/1, Class 2.
What Does Type 1 / Class 2 mean?
Type 1 means Faced with Aluminum foil on both major surfaces of the foam core. Class 2 means Glass fiber reinforced core foam.
NOTE: Dow currently is the only Polyiso foam insulation board manufacturer that makes Type 1 / Class 2 products. The combination of foil facers, glass fiber reinforced core and the unique free-rise process contributes to a product with better foam consistency, durability and fire performance versus generic ISO products.
Specific Approval in IRC & IBC for exposed use without a thermal barrier:
In the 2003 IRC section R 318.3 "Specific Approval" section which states "Plastic foam not meeting the requirements of Sections R 318.1. and R 318.2 may be specifically approved on the basis of one of the following approved tests: ASTM E 84, FM 4880, UL 1040, ASTM E 152, or UL 1715, or fire tests related to actual end-use configurations. The specific approval maybe based on the end use, quantity, location and similar considerations where such tests would not be applicable or practical. Below THERMAXTM meets the majority of those tests listed in the IRC. In the IBC 2003 THERMAXTM meets the requirements of Chapter 26 Plastics, specifically under section 2603.5.3 "Potential Heat" per NFPA 259 and section 2603.8 "Special Approval" for use without a thermal barrier covering.