Split Overflow Drain pipe?

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John McMullen

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Hello,

If you have a 6" overflow drain pipe, is it acceptable to split it into (2) 4" vertical pipes and (2) 4" lambs tongue downspout nozzles right at the exterior wall?

(2) 4" pipes will handle the GPM and roof square footage capacity by code.

Has anyone done this before? I don't know the code says anything about it.
 

frodo

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NO
You can not reduce the size of the piping in the direction of the flow
Chapter 11, Storm Drainage. IPC [Colorado]
1101.5--change in size
1101.6-- fittings and connections

You can buy a 6'' lambs tongue to trim the pipe as it exits the wall
 
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breplum

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It can be dangerous to do a recuction split in the horizontal line even with equal volume, because, unless you can find an eccentric reducer, you end up causing flow resistance.
If you can do it on the vertical in a wall then you ought to be ok.
We've done split reductions for runs under a sidewalk where we don't want a 4" diameter pipe, so we split into two smaller sizes.
 

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