Roof area dividers can perform important functions as parts of
roof systems. For example, in regions where there are periods of
freeze-thaw cycles, area dividers may be used to relieve thermal
stresses on roof systems where expansion joints are not required.
Additionally when reroofing is done in stages, area dividers can be
used to separate roof system sections that differ in age or type.
Area dividers also can be used to isolate a specific area on a roof
system, such as damaged materials around an exhaust vent. Detail
MB-9A, "Torch-applied Flashing at Area Divider in Roof System" in
Roofing Manual: Membrane Roof Systems—2007 provides
recommendations for proper installation of area dividers.
An area divider consists of a vertical double-wood curb that
should be properly anchored to a roof deck. Horizontal wood nailers
should be attached to the vertical nailers' base to provide lateral
support and a location for attachment to the roof deck. The
horizontal nailers should be equal in height to the insulation so a
level transition exists from the insulation to the area divider.
This allows for a more successful roof membrane installation. An
area divider should not be installed on top of insulation;
insulation will not provide adequate compressive strength to
support an area divider.
Similar to all flashing installations, an area divider should
extend a minimum of 8 inches above a finished roof system to
provide adequate flashing height. Also, NRCA recommends an area divider be
covered with a sheet-metal cover. Typically, a sheet-metal cover is
attached on an area divider's vertical legs with exposed gasketed
fasteners; cleats are needed unless unique...
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