Untitled - National Roofing Contractors Association

change. such as a heated office abutting an unheated
warehouse. canopies. etc.
Where movement between vertical walls and the
roof deck may occur
Area Dividers
Where expansion joints are not provided. area dividers
help control the thermal stresses in a roof system (the
term roof system does NOT include the roof deck). They
minimize the transmission of stress from one area of the
roof to another by dividing the entire roof area into smaller
roof sections. These sections should be of rectangular
shape and uniformly spaced where possible. The designer
should determine the respective location and the type
of area divider to be used.
An area divider is designed simply as a raised doublewood
member attached to a properly flashed wood base
plate that is anchored to the roof deck. (See NRCA Construction
Details.) Depending on climatic conditions and
area practices, area dividers for attached membrane systems
are generally required at 150- to 200-foot intervals.
They should be located between structural roof expansion
joints. They should not restrict the flow of water.
The use of elastic preformed "control" joints that are
designed to be installed in the flat plane of the roof is
not recommended because roof system movement may
result when these units are used. The use of raised curb
area dividers is consistent with good roofing practice.
VIII. MECHANICAL CURBS AND
PENETRATIONS
To avoid deflections damaging to the roof, the structural
design of the roof should always allow for the concentrated
loading of mechanical equipment. Vibrations from
roof-mounted or joist-mounted mechanical equipment
should be isolated from the membrane and flashing.
Some equipment may allow moisture to enter the building
either from the exterior or from condensation within.
It is imperative that mechanical equipment housings be
watertight. Water discharge from mechanical equipment
should not be allowed on the roof surface.
When large mechanical units are used, drainage crickets
should be provided around the units to allow adequate
drainage of these areas. Mechanical units should
not restrict the flow of water. Adequate space should be
provided between mechanical units, penetrations and
walls so that roofing materials can be installed correctly.
Units using curbs that have built-in metal base flashing
flanges are difficult to seal and, therefore, are not recommended
for use. Composition base flashing should extend
a minimum of (a nominal) 8 inches above the roof
line. Wood or fiber cants must be provided at any
9O-degree angle created by rectangular curbs or projections.
Wood nailers should be provided on all prefabricated
curbs. The composition flashing (base flashing)
should be fastened either with 1-inch, solid cap-head
nails or with nails driven through tin discs. The nails
should be spaced approximately 8 inches apart.
On mechanical units, two-piece metal counterflashing
should be installed over the base flashing. On units that
will be frequently serviced, the counterflashing should
extend down over the cant to the roof line so that no base
flashing is exposed.
Penetrations around short pipe projections may be
flashed into the membrane by using soft metal or lead
flashing with integral flashing flanges stripped into the
membrane. Good practice dictates that curbs be
placed around all penetrations; the use of so-called
"pitch boxes" or "pitch pockets" around penetrations
should be avoided because they pose a constant
maintenance problem. Projections should not be
located in valleys or drain areas. Adequate space should
be provided between pipes, curbs and walls to allow for
the installation of roofing materials.
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