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Discussion Starter · #1 ·
Hello everyone, I have a question about how are multiple interior roof drain pipes connected together under a very large flat roof, is through horizontal pipes connected below the ceiling and to another pipe in a chase wall?
 

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Low Slope Roofing
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Depends on the situation, some all run together in side a joist space, other times they are run separate down inside walls and connected to the sewer or exterior drain.

Depends oh how far apart the drains are spaced, and a whole lot of other factors.

I take it there is some kind of issue with them?
 

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Discussion Starter · #5 ·
Thanks Windows On Wash and 1985gt. There will be about 50 to 60 feet apart,with about 6 to 7 drains. Trying to minimizing the amount of chase walls.

I was asking is it standard practice or rather is it possible to link them together through horizontal piping which will be concealed by a drop ceiling and have them connect to a main vertical pipe ?
 

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I'd start checking with plumbers, engineers and your local code department. You can find simple drain calculators on line to give you a head start but it may not be possible to route all of them in to one depending on local rain fall and roof size.
 

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Discussion Starter · #9 ·
Thanks 1985gt, I figured by the looks of things some will be routed and others through chases.

Can individual drains have slight horizontal run and then bend down vertical?
 

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I'd start checking with plumbers, engineers and your local code department. You can find simple drain calculators on line to give you a head start but it may not be possible to route all of them in to one depending on local rain fall and roof size.
This is where you need to start.
Rain water leaders are sized based on your area rainfall and square footage of roof and square footage of parapet walls that shed water to the roof surface. Also a consideration is the slope/pitch/grade of the leader line.

Roof drains also need a secondary overflow system. 2 possible methods- seperate roof drains set slightly higher than the main drain bodies and piped like the main drains, except they terminate to daylight- not the storm system.
The other method is the use of scuppers out the side walls.
 

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It is better said that every flat roof needs an overflow system- a secondary drain for emergency.
If you decide to use roof drains for that purpose, then they will pipe into an independent system- not connected to the normal roof drains.

You probably know what a scupper is. that is the other method for an overflow.

The reasoning behind both methods is that in theory, your main roof drain leaders can back up at any spot- underground, in the ceiling or at the drain body itself.
If this happens the overflows or scuppers will take over. They will also be visible and draw your attention to a drain issue.
Water is heavy when spread out over a roof area. Some roofs have collapsed due to ice dams at drains or excessive leave build, etc.

As mentioned earlier- best to have a plumbing/mech. engineer design your system based on the roof area and your annual rainfall.
 
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