Question:
Is it the intent of 1503.4.2.1 Overflow scuppers to be installed 2"-4" above the primary roof drain/scupper height?
Comment:
Allowing overflow scuppers to be installed as currently written "2-4" above the roof deck" can on some buildings allow significantly more dead load of rain water to accumulate by this statement. See illustration attachment.
Existing Interpretations and/or Declaratory Statements Related to this request
Input Received:
A qualified, yes. The cited section of the code does not indicate placement of the overflow scupper as 2”-4” above the primary roof drain/scupper, as reflected in the question. Instead, the code section indicates 2”-4” above the “finished roof covering”. Nevertheless, other sections of the building code must also be in compliance.
According to Chapter 1611, FBC, B, “Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked, plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow...” Overflow scupper size, flow rate and hydraulic head must be established in order to calculate the design rain load. Consequently, the placement of the overflow scupper may be the determining factor in establishing the structural capacity of the deck.
Roof drainage design is complicated and made more so by requirements not being found in a single location in the Florida Building Code (FBC), instead provisions are found in Chapter 15 and 16 (FBC, B) and Chapter 11 (FBC, P) as well as in ASCE 7. As a result, one must look to all relevant code sections to adequately address roof drainage requirements. Additionally, multi-discipline collaboration between the Architect, Structural Engineer, Mechanical/Plumbing Engineer, the plumbing contractor and the roofing contractor is also necessary.
I agree
Answer:
A qualified, yes. The cited section of the code does not indicate placement of the overflow scupper as 2”-4” above the primary roof drain/scupper, as reflected in the question. Instead, the code section indicates 2”-4” above the “finished roof covering”. Nevertheless, other sections of the building code must also be in compliance.
According to Chapter 1611, FBC, B, “Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked, plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow...” Overflow scupper size, flow rate and hydraulic head must be established in order to calculate the design rain load. Consequently, the placement of the overflow scupper may be the determining factor in establishing the structural capacity of the deck.
Roof drainage design is complicated and made more so by requirements not being found in a single location in the Florida Building Code (FBC), instead provisions are found in Chapter 15 and 16 (FBC, B) and Chapter 11 (FBC, P) as well as in ASCE 7. As a result, one must look to all relevant code sections to adequately address roof drainage requirements. Additionally, multi-discipline collaboration between the Architect, Structural Engineer, Mechanical/Plumbing Engineer, the plumbing contractor and the roofing contractor is also necessary.
