Flooding into garage and basement

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bkselly

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I would appreciate some insight into potential causes of flooding / sewage back up in my basement. Over the last year, we've had three separate incidences of flooding, each with a seemingly different cause.

About a year ago, I moved into a 90yr old townhouse where the sewer line goes into the ground/pit in the front of the house (in the garage). Immediately behind the garage is a basement with a bathroom, and toward the other end of the basement is the mechanical room. In front of the garage is a big tree. The house is on a hill where the garage/front is street level, the basement is slightly above the garage, but is almost completely underground once you get to the mechanical room.

In late 2022, the sewage line in the garage backed up and flooded. The water in the garage pooled up in the area where the sewer line cleanout is until it spilled over into the garage. We called a plumber who snaked the line both toward the street and toward the rest of the house, and he said that there were tree roots that he cleared out.

In March 2023, the same thing happened, sewage line in garage backed up and basement bathroom flooded (we couldn't visually identify the source of flooding in bathroom), and this time a different plumber was called who snaked the drain and said there were multiple wipes but did not say anything about roots. We instructed everyone in the house to not throw wipes into the bathroom.

About a few weeks ago we had two straight days of downpour, and by the second day in the afternoon, the basement (and basement bathroom) had flooded (1cm of water in depth). For reference, prior flooding was not preceded by rain. We tried to mop up the water and after an hour of progress, a pool of water reappeared, spreading throughout the basement floor. It looked like the water was coming from the mechanical room in the back side of the basement/house. Interestingly, the garage didn't flood but the cleanout pit did have a bit of water visibly gurgling at the very bottom. There is a pipe that looks like the thickness of a sewer line coming from a wall in the mechanical room going into the ground, but it was very difficult to tell if the water was coming out of the pipe, or the ground itself, since there was about a centimeter height of water visibly exiting the mechanical room into the rest of the basement. A next door neighbor (in an attached house) did not experience any flooding.

I've talked to a couple of plumbers but everyone is suggesting something different whether it's snaking the sewer line, installing a backflow preventer valve, or installing a sump pump. Given the different recommendations, I wanted to check with this forum as to what the most likely issue is and how to best solve it.
 

Jeff H Young

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There is a stoppage likely roots , but broken or open pipe some where as well .
 

John Gayewski

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Sounds like a root problem I highly doubt the first guy got all of the roots unless he was there pulling them out for hours.

Also sounds like there is a seperate water infiltration problem. Do you have gutters? Where do they go? Are they tied into your sewer piping? Are the gutters plugged?

You basically need to figure out where all of your runoff water goes during a rain. It could easily be running down the basement walls and bleeding in through cracks that have formed over the years. I know when my gutters get leaves in them we will get some water in a small area of my basement.
 

Reach4

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When flooding happens after a downpour, it may be the sewer backing up. It's bad enough to have a backup of your own waste, it is worse to get the neighbor's.

If you get backups from the sewers, the best solution is "overhead sewers". If that is a new term for you, check it in your favorite search engine. That means that the ground floor and above feed to the sewer with gravity, and the basement stuff pumps up from a septic pit.

If the floor of your basement is lower than the lowest floor of the neighbors, your basement can serve as a relief for the neighbors. If everybody has basements, then if there is a slope, the lowest house takes the sewage. If the lowest house gets a fix, the problem moves uphill.

There are lesser solutions. If you rely on a backwater valve, it should be a "normally open" type. The flappers nearly always fail to close completely after time. Feeding only the basement waste thru the backup valve is strongly preferred.

Some cities have programs that pay for part of the cure. I don't find one for NYC, but that does not mean that it does not exist. Your local sewer department can be helpful.
 
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bkselly

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@John Gayewski - I think you may be correct regarding run off going down basement walls. Two plumbers indicated that the walls are yellow/look like they have had water exposure. There is a pit where the basement windows are located. I will have to clear that out of leaves, check if there is any where for the water to go there, and check the walls there but it looks like there may be some cracks - I think that may be where the water is coming through
 

Jeff H Young

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I was thinking the storm could have dumped a lot of water in sewer and it backed up because of roots and has damaged lines but all are possibilitys , bad sewer roots or whatever plus another problem but more than just roots . because that alone wont put water on the floor somewhere water is getting out of the pipes
 

bkselly

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It flooded again today, but I was able to get a plumber in as it was happening - turns out there is a small covered pit with an access to the drain between the mechanical room and the laundry closet that I had zero idea about. When the plumber opened the covering, you could see the water overflowing. He pulled out a bunch of dirt (it stacked up about 6-9 inches) and now the water runs freely. Hope this solves the problem - thank you all
 

Jeff H Young

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It flooded again today, but I was able to get a plumber in as it was happening - turns out there is a small covered pit with an access to the drain between the mechanical room and the laundry closet that I had zero idea about. When the plumber opened the covering, you could see the water overflowing. He pulled out a bunch of dirt (it stacked up about 6-9 inches) and now the water runs freely. Hope this solves the problem - thank you all
its just a pit with no watertight lid ?
 

bkselly

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its just a pit with no watertight lid ?
That is correct - the pit just has a loose covering that was overlaid with a few pieces of tile that make up the finished basement floored. It should have a watertight covering?
 

WorthFlorida

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So many things that can cause water in a basement. NYC probably still has too many homes who downspouts from rain gutters are connected to the city sewer system. That will easily cause the sewers to back up especially after 2 days of rain. A sewer back flow preventer is about the only thing that might stop it. I say might because it needs annual checking and cleaning because debris can prevent the flapper from closing. Tree roots can also plug up the back flow preventer. Another issue is old homes you have either clay or cast iron drain pipe going to the city sewer main. 100 years is about the lifetime expectance for Ci and less for clay. Both will crack allowing tree roots to enter or enter through the pipe connections. A camera scope will confirm if there are problems with the pipe.

Sump pump is the way to minimize basement flooding. Most of the time is comes from ground water under the slab. If the old floor has cracks, it is usually from water pressure under it. For full protection, the outside basement walls the dirt needs to be excavated, the walls water proofed and a french drain installed where the pipe is brought to a pit usually in the basement floor. A pump is then used to pump the water outside.

There is no easy or cheap way of prevent flooding.
 

Jeff H Young

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That is correct - the pit just has a loose covering that was overlaid with a few pieces of tile that make up the finished basement floored. It should have a watertight covering?
sewers are closed off they shouldnt dump into a pit or a ditch. so lifying up a lid and seeing raw sewage flowing isnt the norm it also woud tend to clog up I just dont know what you got going on. NYC style I dont know nothing Ive seen and when the sewer backs up poop comes out on floor must be something wrong but evedently the NYC plumbers havent blinked an eye about it?
 
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