CEMP-ET
EI 01S908
1 June 1998
other features that are not necessary to specify architectural requirements. The new NRCA
manual (available in hardcopy and electronic versions) is one source for generic roofing details.
While the NRCA manual is an excellent source for most roofing details, Structural Standing
Seam Metal Roof (SSSMR) system details may have to be obtained from other sources,
including reputable manufacturer's details if nonproprietary. Manufacturers will usually insist on
using their details for their SSSMR system if they warrant the roofing system. This is acceptable
if outlined in the specifications. As a minimum, each change of slope should be detailed. The
details put on the contract drawings should be complete and include all fastening, sealing, or
other requirements to fully construct the SSSMR system. If secondary flexible (EPDM or other
flexible-type) flashings or other type secondary waterproof membranes are shown on the
drawings, the manufacturer should be required to provide them.
(2) Color Considerations. White or light-colored roofing surfaces are much better at
reflecting sunlight than darker surfaces. Light-colored surfaces keep roofs 20 to 35 degrees C
(68 to 95 degrees F) cooler than dark-colored surfaces, which means less heat will be
transferred to internal building spaces. Demonstration projects have shown that cooling energy
use can be cut by as much as 40 percent when light-colored surfaces are used. Designers
should avoid reflective metal finishes near aircraft runways due to potential reflective glare to
pilots. Coordinate the use of light-colored roofing material with the architectural designer and/or
user.
b. Structural Standing Seam Metal Roof System. An SSSMR is a system of metal roof
panels supported and attached by clips fastened directly to the building structure. Clips are
used to elevate the panels above the structural framing system allowing the roof to float. These
panels are capable of spanning between the structural supports and can resist snow, dead, live,
concentrated, and wind loads without benefit of any substrate material. SSSMR systems
typically are installed over open purlins that use horizontal X-bracing to resist lateral loads, but
may be installed over a metal deck diaphragm. When installed over a metal deck, the metal
decking should be designed to run perpendicular to roof slope and the building supports (bar
joist or other structural members). The purlins should be designed to fit into the bottom flute of
the wide rib-metal decking (Type B). If rolled purlins are used, it may be necessary to invert the
metal decking to accommodate the bottom flange of the purlin. The fasteners then would
penetrate the metal decking and attach to the metal building structure below. If the roof
structure is bar joist, the purlins will be connected with self-drilling/self-tapping fasteners through
the metal decking into each upper chord angle of the bar joist. Fasteners should be placed a
minimum two fasteners every 305 mm (12 inches) on-center into the metal decking for
composite action with the building structural supports. Purlins/sub-purlins will be located a
maximum distance of 750 mm (2 ft. 6 in.) in the high wind uplift edge zones
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\ as designed in
ASCE 7, (eave, rake, corner, ridge, or hips) and a maximum distance of 1.5 m (5 feet) on-center
for the remainder of the roof./1/ Users often want a roof that they can walk on for minor
maintenance without excessive deflection. The best way to achieve this, plus providing the
required insulation, is to use rigid polyisocyanurate on top of the metal decking. (Approximately
75 mm (3 in.) of polyisocyanurate insulation provides an R-20 value). To help assure a leak-free
SSSMR system, an underlayment of 30# felt or an ice/water guard membrane underlayment
may be installed on top of the insulation and is especially recommended along the roof edges,
including valleys, ridges, and hips which are prone to leaking. The added cost of a waterproof
underlayment is minuscule compared to the cost and exasperation of having, finding, and
repairing a leaking roof. While the waterproof underlayment will not assure the SSSMR system
will not leak, it usually results in the water not leaking directly into the building envelope but, to
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