Built-Up Roofing - Page 8

6.15.2 The following JM Specifications are eligible for modification and use with Protected Roofing Membrane Systems: 4GIS, 3GIS, 5GNS, 4GNS, 3GNS, 5GLG, 4GLG. When these specifications are modified, the last digit of the specification number should be changed to a "P" to designate "Protected" (e.g., 4GIP).

6.15.3 Flashings: All flashings must conform to the requirements stated in this Section and the current JM Commercial/ Industrial Roofing Systems Manual. The flashing material must extend above the top of the extruded polystyrene insulation a minimum of 8" (203 mm). The standard flashing details for built-up roofing systems can be found in "Bituminous Flashings", Section 8.

6.15.4 Drainage: Design and installation of the deck and/or roof substrate must result in the roof draining freely, to outlets numerous enough, and so located, as to remove water promptly and completely. Areas where water ponds for more than 24 hours are unacceptable and will not be eligible for a JM Roofing System Guarantee.

6.15.5 When designing a PRMA roofing system, the designer must make sure that positive drainage exists on the roof. Even though some extruded polystyrene roof insulation products are designed with integral drainage channels, they will retard the flow of water due to the contact between the membrane and the insulation. JM recommends a minimum of ¼" per foot (20.8 mm/m) slope be obtained on the finished roof membrane. This will greatly reduce the amount of water that will be retained against the membrane after a rain.

6.15.6 Decks (PRMA)
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. For lightweight insulating concrete, gypsum decks, etc., consult a JM Technical Service Specialist for specifications and guarantee information. For information on roof deck requirements not mentioned, refer to the "Roof Decks" Section of the current JM Commercial/ Industrial Roofing Systems Manual, or contact a JM Technical Service Specialist.

6.15.7 Asphalt Recommendations (PRMA)
Asphalts: The use of ASTM D 312, Type III asphalt is recommended to prevent adhesion of the extruded polystyrene insulation to the asphalt top pour. If a softer asphalt, such as a Type I or Type II is used, a separator sheet MUST be used. The minimum separator sheet is a 4 mil (0.1 mm) polyethylene sheet.

If a Type I or II asphalt is used without a separator sheet, the extruded polystyrene roof insulation can become adhered to the roof membrane. During periods of heavy rain, the buoyancy of the extruded polystyrene can cause strong upward forces to be exerted on the membrane. The buoyancy forces may be so severe as to tear the membrane.

6.15.8 Ballast Requirements (for use with extruded polystyrene roof insulation):

The ballast should be similar to ASTM D 448, Gradation #57. The following gradation is typical:

6.15.9 Ballast is applied at a rate of approximately 10-12 lbs. per sq. ft. (48.8-58.6 kg/m²) in the field of the roof over a layer of filter fabric. Twenty (20) lbs. per sq. ft. (97.6 kg/m²) of ballast is required over a 4' (1.22 m) wide area at the roof perimeter and at all penetrations. The following filter fabrics have been found to be acceptable:

A. Confil 689H – 3.0 oz./yd. (93.5 g/m) black polyester from International Paper Company

B. Rufon P3B – 3.0 oz./yd. (93.5 g/m) black polypropylene from Phillips Fiber Corporation

6.15.10 JM makes no claims as to the quality or performance of these products when exposed on the roof. See the product warranty supplied by the manufacturer.

6.15.11 When pavers are used as ballast, the pavers must be placed on supports or pedestals. These supports or pedestals can either be commercially available products or 6" (152 mm) square pieces of JM DynaTred Plus (to give a minimum ½ " [13 mm] air space). These supports should be located at the intersection of the corners of the paver blocks. All four corners of adjacent pavers should rest on the same 6" (152 mm) square piece of JM DynaTred Plus or pedestal. The ½ " (13 mm) air space between the pavers and insulation will allow moisture vapor to vent to the atmosphere. If the moisture is not allowed to vent to the atmosphere, the top surface of the insulation will begin to absorb water and the thermal performance will be reduced. ROOF AREAS THAT HAVE PAVERS IN DIRECT CONTACT WITH THE INSULATION ARE EXCLUDED FROM COVERAGE IN A JM ROOFING SYSTEM GUARANTEE, INCLUDING THE THERMAL OVERLAY PORTION OF THE GUARANTEE.

6.15.12 The use of pavers in high traffic areas, to and around equipment and other maintenance areas, is strongly recommended.

6.15.13 It is the owner’s and/or specifier’s responsibility to determine if the building structure can support the required amount of ballast and still meet the code design requirements for anticipated dead and live loads (including snow, wind, etc.).