posted
I need help. I recently had a homeowner come in that had had flat roof overflow problems due to a monsoon type downpour we had here in Yuma a couple of weeks ago. He had insufficient drainage through the parapet walls of his flat roof. He wanted to know the requirements for roof scuppers. As I started to reasearch I realized there are no definitive answers to that question. The 2003 IRC, which we are currently in, talks only about "roof slope and contributing roof area" without giving any formulas for figuring opening area. Going to the 2003 IBC Sec. 1503.4 "Roof drainage" it refers me to the IPC for roof drainage systems. Well, guess what, the IPC refers me back to the IBC for parapet wall roof drainage scuppers and overflow scupper design. As far as I can see, the only elements that the IPC talks about are gutters and downspouts. Any help would be greatly appreciated
Posts: 10 | From: Yuma, AZ. | Registered: Mar 2006
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"R903.4 Roof drainage. Unless roofs are sloped to drain over roof edges, roof drains shall be installed at each low point of the roof. Where required for roof drainage, scuppers shall be placed level with the roof surface in a wall or parapet. The scupper shall be located as determined by the roof slope and contributing roof area."
"R903.4.1 Overflow drains and scuppers. Where roof drains are required, overflow drains having the same size as the roof drains shall be installed with the inlet flow line located 2 inches (51 mm) above the low point of the roof, or overflow scuppers having three times the size of the roof drains and having a minimum opening height of 4 inches (102mm)shall be installed in the adjacent parapet walls with the inlet flow located 2 inches (51 mm) above the low point of the roof served. The installation and sizing of overflow drains, leaders and conductors shall comply with the International Plumbing Code.
"Overflow drains shall discharge to an approved location and shall not be connected to roof drain lines."
I'd design the scuppers to comply with the requirements for overflow scuppers, except that the scupper is placed level with the roof per R903.4. An overflow scupper (or overflow drain) is not required because they are only necessary where "roof drains are required."
posted
Thanks to Mule and RLGA for the response. I think I might have explained poorly. I'm looking for something that would tell me the amount of net opening for scuppers based on sq ft of roof area, slope and rainfall per hr.
Sec.1611 is based on design for water retention. I want to get it off the roof in a timely manner.
And based on Table 1106.3 in the 2006 IPC a 1546 sq ft roof with 2% slope at 3 inches per hr of rainfall would only need (1) 3" diameter drain (scupper). Unless I'm reading something wrong, which could be a possibility, that seems woefully undersized.
BTW, RLGA, I'm just a recent Yuman. Only been here 7 years. But I think that's an awesome name for a high school mascot. Do you know the story behind how they got there name ?
Posts: 10 | From: Yuma, AZ. | Registered: Mar 2006
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posted
The UPC addresses this pretty well. Even if you haven't adopted the UPC, it makes a good reference. I don't have mine handy (Saturday!) but otherwise I'd cite the section.
-------------------- CBO, MCP, LEED AP Posts: 748 | From: North Las Vegas, NV | Registered: May 2006
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