Which material is least likely to be used as insulation in low-slope roofing?

Fiberglass batt insulation is least likely to be used as insulation in low-slope roofing systems. This is primarily due to the installation challenges and performance characteristics of fiberglass batts in these applications. Fiberglass batts are typically designed for use in framed assemblies where they can fit snugly between studs or joists. In low-slope roofing contexts, the insulation needs to maintain its position and be effective in minimizing thermal bridging while also accommodating potential movement or settling of the roofing system.

Low-slope roofs often utilize materials that are more compatible with the roofing system itself, such as rigid board insulation, spray foam insulation, or mineral wool insulation. These materials can be installed more readily in a continuous manner, providing a better thermal barrier without gaps or compression. Additionally, rigid board insulation and spray foam can adhere directly to the roofing deck, helping to avoid issues related to water penetration and maintaining the thermal performance in areas that are prone to moisture. Mineral wool also offers advantages such as fire resistance and water resistance, making it a more suitable choice in low-slope applications compared to fiberglass batts.