1.2
DESCRIPTION OF ROOF MEMBRANE SYSTEM[S]
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NOTE: Coordinate with Part 2 materials
specification.
Where one membrane system is required for all roof
areas, use the first paragraph. Where different
systems are required, use the second paragraph
successively and replace the open brackets with a
description of the substrate(s) or area of the
building or project where each system is to be
applied.
Specify the three-ply option including base sheet,
interply sheet and cap sheet when mechanical
fastening of bottom ply is required either directly
to nailable deck or over insulation substrate and
into nailable deck, and when perforated base sheet
is used. Otherwise, specify two-ply option including
modified bitumen base sheet and cap sheet.
Two-ply option may also be considered when the
mechanical fastening of the modified bitumen base
ply is concealed in the finished base ply
installation (i.e., no exposed fasteners in the base
ply prior to application of cap sheet such as occurs
in base sheets fastened only in the side lap area
and where the overlapping adjacent base sheet is
torch sealed over the fasteners in the lap area).
One ply modified bitumen roof membrane shall not be
specified without prior Government approval and
shall only be considered for application on open air
sheds or light storage structures and ancillary
buildings of little importance. One ply membrane
includes application of a single ply directly to
deck or insulation substrate or over mechanically
fastened or perforated base sheets.
Specify SBS for all hot asphalt membrane
applications. Torch applied and cold adhesive
applications may include either or both SBS and APP,
selected based on the specific application and
service conditions intended. APP systems are
allowed on Army projects only.
Felt base sheet may be specified in a low to
moderate service three-ply application. Specify
venting base sheet for application directly to new
concrete deck and over nailable lightweight fill
substrate materials.
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Minimum [two-ply][three-ply] SBS [or] [APP] modified bitumen roof membrane
consisting of [modified bitumen base sheet][fiberglass felt [venting ]base
sheet] [,interply sheet] and cap sheet. Modified bitumen roof membrane
shall be [set in hot asphalt][torch applied][set in cold-applied adhesive].
SECTION 07550
Page 7
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