Secondary (Emergency) Roof Drains
Secondary (Emergency) Roof Drains
(OP)
Does anyone have experience designing storm drainage systems using scuppers only?
I am designing the storm water drain system for the roof of a two story building (I-2) and our client requested replacing the roof drains by scuppers. We are using the 2012 International Plumbing code and I am sizing the scuppers according to Figure 1108.3 in the IPC Commentary which is based on Francis formula:
http://www.engineeringtoolbox.com/weirs-flow-rate-...
My question is, since we are only using scuppers, do we need a secondary (emergency overflow) system, i.e. additional scuppers discharging above grade?
From IPC 2012:
SECTION 1108 SECONDARY (EMERGENCY) ROOF DRAINS:
1108.1 Secondary (emergency overflow) drains or scuppers.
Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.
1108.2 Separate systems required.
Secondary roof drain systems shall have the end point of discharge separate from the primary system. Discharge shall be above grade, in a location that would normally be observed by the building occupants or maintenance personnel.
Thanks in advance!
Attached is a picture that I found on the internet depicting scuppers as primary and secondary roof drainage systems.
I am designing the storm water drain system for the roof of a two story building (I-2) and our client requested replacing the roof drains by scuppers. We are using the 2012 International Plumbing code and I am sizing the scuppers according to Figure 1108.3 in the IPC Commentary which is based on Francis formula:
http://www.engineeringtoolbox.com/weirs-flow-rate-...
My question is, since we are only using scuppers, do we need a secondary (emergency overflow) system, i.e. additional scuppers discharging above grade?
From IPC 2012:
SECTION 1108 SECONDARY (EMERGENCY) ROOF DRAINS:
1108.1 Secondary (emergency overflow) drains or scuppers.
Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.
1108.2 Separate systems required.
Secondary roof drain systems shall have the end point of discharge separate from the primary system. Discharge shall be above grade, in a location that would normally be observed by the building occupants or maintenance personnel.
Thanks in advance!
Attached is a picture that I found on the internet depicting scuppers as primary and secondary roof drainage systems.





RE: Secondary (Emergency) Roof Drains
In general, you have to have secondary drainage of some sort because of the parapet as stated in 1108.1. If one scupper gets plugged, the area covered by the scupper could accumulate water and cause issues depending on the roof design (IPC 1101.7).
Normally, secondary drains are designed to allow for 2"-4" of ponding on the roof before water enters, assuming the structure of the roof area can support that much water. So the bottom of the secondary scupper would be higher by that much.
Make sure the scuppers are located per 1106.5
Although the argument could be made that it is highly unlikely a scupper (or all scuppers) would be plugged since it does not have a strainer. Also the argument could be made that any accumulating water would flow over the top of the roof pitch point and be directed to a nearby scupper. The structural engineer would have to prove the roof structure could support the accumulated water.
But that argument might be lost with the plumbing code official.
RE: Secondary (Emergency) Roof Drains
RE: Secondary (Emergency) Roof Drains