7A.35 Decks (PRMA)

7A.35.1 Pre-cast slabs and pre-stressed "T" or "TT" decks require a minimum of one layer of approved JM roof insulation as a leveling course prior to the installation of the roof membrane.

7A.35.2 For lightweight insulating concrete, gypsum decks, etc., consult a JM Technical Service Specialist for Specifications and Guarantee information.

7A.35.3 For information on roof deck requirements not mentioned here, refer to the "Roof Decks" section of the current JM Commercial/Industrial Roofing Systems Manual, or contact a JM Technical Service Specialist.

7A.35.4 Warning: Extruded polystyrene insulation is combustible and may constitute a fire hazard if improperly used or installed. It should be adequately protected. Use only as directed by the specific instructions for this product. This material should NEVER be exposed to an open flame or other source of ignition.

7A.35.5 All roof deck systems over which the protected system is installed should provide an adequate fire barrier for the extruded polystyrene insulation.

7A.35.6 For proper protection of plastic foam in storage, consult the National Fire Protection Association (NFPA) standards or the authority having jurisdiction.

7A.36 Installing Ballasted PRMA Roof Insulation Over Modified Bitumen Roof Membranes

7A.36.1 The following are general recommendations for installing ballasted PRMA roof insulation over modified bitumen roof membranes.

Materials per 100 sq. ft. (9.29 m²) of Membrane Area

*Additional ballast is required at the perimeter and at penetrations.

7A.36.2 Insulation: Place extruded polystyrene roof insulation directly on the membrane with channel side down. The insulation boards should be tightly butted together. The maximum allowable gap between boards is 3/8" (9.5 mm). The boards shall be installed to within approximately 3/4" (19 mm) of, but not touching, projections and cant strips.

7A.36.3 For multilayer installations, install subsequent layers, unattached over the first layer. Stagger all joints in relation to the underlying layer. The bottom layer in multilayer applications must be at least 2" (51 mm) thick and as thick or thicker than the top layer.

7A.36.4 Fabric: Loose lay an approved fabric over the extruded polystyrene roof insulation, with all joints lapped a minimum of 12" (305 mm). There should not be any end laps within 6 feet (1.83 m) of the perimeter. The fabric should extend 2" to 3" (51 - 76 mm) above the stone at the perimeter and at penetrations.

7A.36.5 Wetting the fabric is helpful in holding it in place on the insulation until the ballast is installed.

7A.36.6 Ballast: Apply the correct size ballast at the rate of 1000 -1200 lbs. per square (10 - 12 lbs. per sq. ft. [48.8 - 58.6 kg/m²]), over the fabric, as the fabric is being laid out in the field of the roof. For a width of 4 feet (1.22 m) at the roof perimeter or penetrations, install ballast at a rate of 20 lbs. per square foot (97.6 kg/m²) orpavers at a rate of 22 lbs. per linear foot (32.7 kg/lin. m). If pavers are used, the fabric is not required. Pavers must be placed on pedestals. Pedestals can be either commercially available products or 6" (152 mm) square pieces of JM DynaTredPlus.

7A.36.7 Ballast should be washed 3/4" (19 mm) gravel or crushed stone, with fines (smaller than 1/2" [13 mm]) accounting for not less than 10% or more than 60%. This gradation is similar to ASTM D 448, Gradation #57.

7A.36.2 Insulation: Place extruded polystyrene roof insulation directly on the membrane with channel side down. The insulation boards should be tightly butted together. The maximum allowable  gap between boards is 3/8" (9.5 mm). The boards shall be installed to within approximately 3/4" (19 mm) of, but not touching, projections and cant strips.

7A.36.3 For multilayer installations, install subsequent layers, unattached over the first layer. Stagger all joints in relation to the underlying layer. The bottom layer in multilayer applications must be at least 2" (51 mm) thick and as thick or thicker than the top layer.

7A.36.4 Fabric: Loose lay an approved fabric over the extruded polystyrene roof insulation, with all joints lapped a minimum of 12"  (305 mm). There should not be any end laps within 6 feet (1.83 m) of the perimeter. The fabric should extend 2" to 3" (51 - 76 mm) above the stone at the perimeter and at penetrations.

7A.36.5 Wetting the fabric is helpful in holding it in place on the insulation until the ballast is installed.

7A.36.6 Ballast: Apply the correct size ballast at the rate of 1000 -1200 lbs. per square (10 - 12 lbs. per sq. ft. [48.8 - 58.6 kg/m²]), over the fabric, as the fabric is being laid out in the field of the roof. For a width of 4 feet (1.22 m) at the roof perimeter or penetrations, install ballast at a rate of 20 lbs. per square foot (97.6 kg/m²) orpavers at a rate of 22 lbs. per linear foot (32.7 kg/lin. m). If pavers are used, the fabric is not required. Pavers must be placed on pedestals. Pedestals can be either commercially available products or 6" (152 mm) square pieces of JM DynaTredPlus. 

7A.36.7 Ballast should be washed 3/4" (19 mm) gravel or crushed stone, with fines (smaller than 1/2" [13 mm]) accounting for not less than 10% or more than 60%. This gradation is similar to ASTM D 448, Gradation #57.