December 2007
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Roof area dividers | Technical Elements

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Roof area dividers

by James R. Kirby, AIA
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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 The NRCA Roofing Manual: Membrane Roof Systems—2007 provides recommendations for proper installation of area dividers.

Detail MB-9A, The NRCA Roofing Manual: Membrane Roof Systems—2007

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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