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August 25, 2007
On flooded cellars...
Please note, if you can’t click the links to open them, you’ll have to copy and paste them to your browser.
This is a very basic piping schematic of what exists in most brownstones in our area.
It shows, from left to right: The pipe's terminal to the street, the trap, the fresh air inlet from outside, a half-bathroom group in the cellar, a waste stack serving the upper floors, then another trap for the storm or leader drain from the roof of the building.
As I said, it's very basic.
http://i31.photobucket.com/albums/c360/ciaony/buildingdrainagesystem-oldcode2.jpg
Lots of people call me after a heavy rain and want to know what they can do about the water that comes out of the drain, either through the cellar fixtures or some other outlet.
Inevitably, the homeowner mentions installing a check valve (sometimes called a backflow/backwater valve and various other names).
The place for a check valve is on the pipe just to the left of the trap.
Like this:
http://i31.photobucket.com/albums/c360/ciaony/buildingdrainagesystem-oldcodewithc.jpg
Having it there will keep water from the flooded city sewers from entering your building.
The only problem is, when the valve activates it closes and doesn't allow the flow of water in either direction through the pipe.
So now that it's raining and the pipe is closed off, where does all that water go that's coming in from the roof (the pipe on the far right)?
The answer is....all over your floor.
There is a solution.
See it here:
http://i31.photobucket.com/albums/c360/ciaony/buildingdrainagesystem-newcode-1.jpg
Comments
Well, that went about as well as I'd expected....
Anyway, the last link shows the storm water drain relocated to in front of the building's trap and check valve.
This configuration, minus the check valve, is what our current plumbing code calls for.
Makes sense?
Posted by: Master Plvmber at August 25, 2007 7:59 AM
Master Plvmber - your posts if not the most useful on this site, are surely a strong contender. Very useful, thank you
Posted by: guest at August 25, 2007 9:40 AM
Thank you Master Plumber...
Posted by: CrownGardener at August 25, 2007 9:56 AM
Master Plvmber, in the new code is the storm water supposed to connect directly into the sewer (thus requiring the street to be dug up) or can it join the existing house connection as I interpret your drawing.
Thanks for the great schematic.
Posted by: an architect in Brooklyn at August 25, 2007 12:10 PM
The two can be combined inside the building to form a "combination sewer" as defined by code.
Posted by: Master Plvmber at August 25, 2007 2:40 PM
Not that MP needs the cred...
...but he did do this very setup in my basement, and it works great. The last big storm we had no water!!!
Posted by: guest at August 25, 2007 3:44 PM
Do I understand this correctly? You run a separate line from the rain gutter through the cellar, above the sewer line, and connect it to the outgoihng sewer line on the other side of the check valve? Is this legal (to code)? Both Vigilante and Figliolia told me it had to connect to the sewer line in the back of the house.
Posted by: guest at August 25, 2007 5:29 PM
You've got it exactly and it's to code.
Can't comment on what others told you, but I will say that in many cases to do this properly, some excavation is required.
Posted by: Master Plvmber at August 25, 2007 5:39 PM
A friend sent me this thread. Here's the flaw in the logic: If the check valve has flipped, it's because the sewer water has backed right up against the valve...which means the run off rain water from the roof still has nowhere to go, and worse, you will start to get the sewer water back up into the line that connects to your outside downspout.
Posted by: guest at August 25, 2007 9:46 PM
...but keep it out of the house.
Posted by: Master Plvmber at August 25, 2007 11:26 PM
Thanks very much to take the time to post these schematics, but I would have to agree with the above poster who points out the flaw in the logic. All that water coming from your roof(many 100s of gallons) will have nowhere to go and so it will start to cascade down the back of your building. Who knows what opening the water will find in your building (it always does find one) particularly once it hits the ground right next to your building. Even if water is not entering the building today, eventually it will find a way in.
Posted by: guest at August 27, 2007 10:13 AM
Forgive me if I'm off base, learning this as I go along - and write checks.
I have a drain in my basement (hidden under a rather expensive and permanent floor, don't ask.) When it rains really hard rain water seems to flow out of the drain and into my otherwise dry basement. Sessa plumbing said it's because that drain is connected to the sewer line Which is under the concrete in the basement floor and that line connects to the storm drain as the storm drain tilts down and out of the house.
Now, when it rains the proverbial cats and dogs, storm water is backing along the swer line and into the basement. Because no one's using the loo (thank god) all we're getting coming out of the drain is storm water.
According to Sessa, answer is to install a valve on this sewer line that closes when storm water hits it from the other side. Granted the sewer line would theoretically back up if we used the loos then but that doesn't sound like as big of a headache as bailing 9 inches of water out of the basement.
Any of this jive with what's being said above?
Posted by: Johnny at August 27, 2007 11:19 AM
Alright, what you have to understand is that when water gets too high, there is NOTHING you’re going to do to stop it.
All the neighborhood flooding we’ve been watching on the news? Those people have flooded basements and a lot of damage. This piping configuration will not help, and is not intended to help, that type of condition.
What this does help is where the sewers in the street are flooded and the pipes in our homes are filled to capacity.
In our area, it doesn’t tend to get much worse than that and that’s why this code was written.
The water stacking up from the leader line MAY eventually over flow into the yard, it’s true, but only until the city sewers can take on more water. That’s a much smaller problem than the one that is solved.
And the last poster is right, as I read his post, when the check valve is closed, water use in the building could result in an over flow in the building drain.
There are some devices on the market now that will activate a valve on the water main to turn it off when the check valve is closed. It is a very expensive installation and in my opinion, not worth the cost.
Again, this is to prevent building flooding in our area’s typical “flash flood” type of storm. For water from the city sewer to be so high as to back up into the building's leader line, you can bet we'd have even bigger problems than that at that point.
There is no safeguard against Armageddon.
Posted by: Master Plvmber at August 27, 2007 11:51 AM
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