Min. 1.5-inch EnergyGuard Polyiso Insulation, EnergyGuard Ultra Polyiso Insulation, EnergyGuard RA, EnergyGuard RH, EnergyGuard RN LRF-M, OB500, GAF 2-Part or CR-20 Min. 0.5-inch Dens Deck LRF-M, OB500, GAF 2-Part or CR-20 SBS-AA or APP-TA (Optional) SBS-AA or APP-TA Drainage board and structural concrete topping slab N/A C-3. Structural concrete. Founded in 1886, GAF has become North America's largest manufacturer of commercial and residential roofing. Our success in growing the company to nearly $3 billion in sales has been a result of our relentless pursuit of quality, combined with industry-leading expertise and comprehensive roofing solutions.Whether it's for residential or commercial roofing applications, professional.