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SBS Modified Bitumen
Specifications |
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Specification
2CND/2FND/2PND |
Two Ply Hot Mopped Modified Bitumen Mineral 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.
Base sheets and cap sheets with polyester reinforcement must be allowed
to relax in an unrolled position prior to installation. |
Steep Slope Requirements
Special procedures are required on inclines over 1/2" per foot (41.6 mm/m).
Refer to Paragraph 7A.29.
Surfacing
No additional surfacing is required.
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 cold weather application techniques, refer to Paragraph 7A.31.
