2CNG/2FNG/2PNG. CSI 3-Part Specifications. Large file (>500kB).

Two Ply Hot Mopped Modified Bitumen Gravel Surfaced Roofing System. For use over plywood or other nailable decks on inclines up to 3" per foot (250 mm/m).

For Regions 1, 2 and 3

General

This specification is for use over any type of approved structural deck (without insulation) which can receive and adequately retain nails or other mechanical fasteners that may be recommended by the deck manufacturer. Examples of these decks are wood, plywood, and approved oriented strand board (OSB). This specification is not for use directly over lightweight, insulating concrete decks.

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.

Note:  All general instructions contained in the current JM Commercial/Industrial Roofing Systems Manual shall be considered part of this specification.

Flashings

Flashing details can be found in the "Bituminous Flashings" section of the JM Commercial/Industrial Roofing Systems Manual.

Application

On roof decks with slopes up to 1/2" per foot (41.6 mm/m), the roofing felts and modified bitumen sheets may be installed either perpendicular or parallel to the roof incline.

Over wood board decks, one ply of sheathing paper must be used under the base felt, next to the deck.

Using one of the base felts listed, start with a piece 18" (457 mm) wide. The remaining felts are to be applied full width with 3" (76 mm) side and 4" (102 mm) end laps over the preceding sheets. Nail the laps at 9" (229 mm) centers, and down the longitudinal center of each felt place two rows of nails, with the rows spaced approximately 11" (279 mm) apart, and nails staggered on approximately 18" (457 mm) centers. Use nails or fasteners appropriate to the type of deck, with 1" (25 mm) minimum diameter caps. For additional fastener information, refer to the fastener data in the "Roof Decks" section of the current JM Commercial/Industrial Roofing Systems Manual.

Apply a full width piece of one of the cap sheets listed into a full mopping of asphalt. Subsequent sheets are to be applied in the same manner, with 4" (102 mm) side and end laps over the preceding sheets (6" [152 mm] end laps for DynaLastic products).

Apply all felts so that they are firmly and uniformly set, without voids, into the hot asphalt. Asphalt temperature should be at the Equiviscous Temperature (EVT), ±25°F (±14°C), at the point of application. All felt edges shall be well sealed. The asphalt shall be applied just before the felt, at a nominal rate of 23 lbs. per square (1.1 kg/m²). For modified bitumen sheets, the asphalt temperature shall be at a minimum of 400°F (204°C), or at the EVT, whichever is higher, when the sheet is set into it. This higher temperature maximizes the bonding of the modified bitumen sheet.

Note: When using metric and English sized base and cap sheets in the same system, care must be taken to avoid lap over lap configurations.

For cold weather application techniques, refer to Paragraph 7A.31.

Steep Slope Requirements

Special procedures are required on inclines over 1/2" per foot (41.6 mm/m).
Refer to Paragraph 7A.29.

Surfacing

Flood the surface with the appropriate asphalt, depending on the roof slope, at an approximate rate of 60 lbs. per square (2.9 kg/m²). Embed an acceptable gravel at the rate of approximately 400 lbs. per square (19.5 kg/m²), or an acceptable slag at a rate of approximately 300 lbs. per square (14.6 kg/m²), into the hot asphalt. Aggregate must be installed so that there is complete coverage across the entire surface and at least 50% of the aggregate is solidly adhered in the hot asphalt.

Asphalt

Asphalt should meet the requirements of ASTM D 312.

JM Guarantees require the use of Trumbull asphalt or another JM Approved Asphalt. The Contractor must provide an Asphalt Confirmation Number (ACN) on projects which require a JM Guarantee. The ACN will indicate that the asphalt was registered with the approved asphalt source.

For an identical copy of this specification, ask for RS-4207.