6.15.14 Installing Ballasted, Unadhered PRMA Roof Insulation
Over Built-Up Roof Membranes
The following are general recommendations for installing ballasted PRMA roof insulation over built-up roof membranes.

6.15.15 Separator Sheet: (If required) Over Type I or Type II asphalt, use a 4 mil (0.1 mm) thick (minimum) polyethylene separator sheet installed directly over the asphalt with 2" (51 mm) minimum laps at all seams.

6.15.16 Insulation: Place extruded polystyrene insulation directly on the membrane (or separator sheet if used) 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 and no closer than ¾" (19 mm) of all projections and cant strips.

6.15.17 For multilayer installations, install subsequent layers of insulation, 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.

6.15.18 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.

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

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

6.15.19 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' (1.83 m) of the perimeter. The fabric should extend 2" - 3" (51 - 76 mm) above the stone at the perimeter and at all penetrations.

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

6.15.20 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' (1.22 m) at the roof perimeter or penetrations, install ballast at the rate of 20 lbs. per sq. ft. (97.6 kg/m²) or pavers at the 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) squares of DynaTred Plus.

Ballast should be washed ¾" (19 mm) gravel or crushed stone ¾ " (19 mm), with fines (smaller than ½ " [13 mm]) accounting for not less than 10% or more than 60%. This gradation is similar to ASTM D 448, gradation #57.

6.16 Coal Tar General Information

6.16.1 JM acknowledges that ASTM D 450, Type I Coal Tar Pitch is used in certain gravel surfaced built-up roofing system specifications. However, coal tar pitch is not to be used within JM Roofing Systems.

Danger: Coal Tar is considered a hazard by inhalation, ingestion and skin contact. The International Agency for Research on Cancer (IARC) has classified coal tar as an agent which is carcinogenic to humans (Group 1). JM does not make or sell a coal tar pitch waterprooflng agent, and does not recommend its use. Alternative materials, such as asphalt should be utilized.