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p r o d u c t s
Pressure Coefficients:
Pressure Coefficients, Cp, are obtained from Table 4 (below), whose values are based upon common usage in literature and wind tunnel investigation.
Recommended Pressure Coefficients for Roof Edge Devices, Table 4
| Roof Perimeter Location |
Pressure Coefficient Cp |
Direction of Force |
| Within "Corner" Region |
-2.0
-3.0 |
Outward
Upward |
| Between "Corner" Areas |
-1.6
-2.0 |
Outward
Upward |
In the above Table, "Outward" force is a horizontal force acting perpendicular to the building at the roof edge, tending to pull the roof edge off. "Upward" force is the vertical force acting to pull the roof edge up. The minus sign (-) indicates that the pressure is away from the building, tending to pull materials up or off.
The following criteria are recommended as "minimums" for metal edge securement. Specific project conditions may require higher wind resistance, in which case the building designer should calculate (and design for) the required loads according to local building codes.
A. Membrane Attachment
The design of the metal edge system, when terminating the roofing system, should provide a minimum holding power of 100 pounds per foot, with the force measured in a direction of 45 degrees back onto the roof. SPRI Test MEthod RE-1 is a membrane termination test specifically for fascias that act as terminations for roofing membranes.
The metal edge system is the last anchor point to hold the roofing material in place should the membrane happen to separate from the roof deck during a high wind. When this happens, the roof system will put a load on the termination. For this reason, the roof edge must withstand a minimum force of 100 lbs/ft when tested using the RE-1 Method. SPRI Test Method RE-1
To test this condition, a 12" wide mock-up of the termination system shall be constructed and mounted on the base of a tensile testing device so the roofing material is pulled at a 45" angle to the roof deck, simulating a billowing roof membrane.
The jaws of the tensile tester are connected to two bars which clamp the membrane securely between them so that the load is distributed uniformly along the width of the membrane. The tensile tester is then loaded until failure occurs. Failure is defined as any event which allows the roofing material to come free of the metal edge system, or the metal edge to come free of its mount.
The roof edge termination's "strength" is satisfactory if the test force (at failure) on a 12" wide sample exceeds 100 pounds.
Fascia / Membrane Termination
Test Set Schematic
(Force = F = 100 lbs/ft.)
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