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Since I live on a hill where and because of the way my house is positioned, and I have neighbors behind me and next door, I have to drain forward, towards the sidewalk. I know there are major drawbacks to that though it’s common in my area. However, the downspouts on my house drain into the sewer lines because it got grandfathered in that way.

I’m considering tying my French drain into the pvc pipe my downspout drains into. This would save labor compared to trenching all the way to the sidewalk. Would that work? What are the risks of a sewer back up this way?

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  • Could you add some more details? When I read this over I note that you are on top of a hill so gravity should drain water away without a lot of work. Your downspouts drain into the storm drain but you are worried about sewer backup? Storm and sewer are normally two systems. Are they for you?
    – kevinskio
    Sep 18, 2021 at 0:30
  • @kevinskio, I added some edits and corrects.I believe my down spouts do actually go to sewer line since a plumber was able to get a camera in the downspout I plan to tie into, and it went to the sewer line.
    – LRitter
    Sep 18, 2021 at 10:37

4 Answers 4

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The risk of a sewer backup is almost impossible to answer. It might be fine to add downspout water this year but next year someone flushes a toy down the toilet and there is a torrential rain and bingo! Tree roots, oil or grease and damaged pipes are other causes of sewer backups which you cannot predict.

Instead I recommend a dry well. You must assess what kind of rain is typical for your region and whether you expect unexpected rain events as so many home owners across the world have recently.

The easiest solution is a large plastic pail with bottom removed.

  • Dig a hole a little bigger than the diameter of the pail and about six inches deeper than the height of the pail.
  • Place good quality landscape fabric or geotextile on the bottom
  • Put the pail in the hole
  • Fill with large chunky rocks
  • Top with more landscape fabric
  • Position the downspouts to drain into the pail
  • Fill to surface level with soil and top with gravel or sod

Or you can build something that handles larger quantities of water but takes more digging with a polypropylene cage. This will absorb much larger quantities of water but will cost more and take more effort to install.

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A french drain is an excellent way to deal with downspout water. My step-daughter has one on one side of her house, and it's working so well, we're going to put one on the other side before winter.

But I would cap off the connection to the sewer system. It is unlikely to back up that far — it might be coming up shower drains in that case! But I think you should cap it off anyway, which would then be compliant with non-grandfathered use.

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It is unlikely that your grandfathered downspout-to-sewer allows for you to ADD to the sewer with new construction (such as your planned French drain). Such drainage systems were created back when there was only a single sewer system and not the separate sanitation and stormwater sewers we see today. Most of the single-sewer systems will still discharge into local waterways whenever the system is beyond capacity, such as during heavy rainfall. It is common to grandfather older downspout-to-sewer hookups so homeowners don't have to retrofit their rainwater handling systems, but municipalities would prefer you disconnect your downspout to reduce the load on their sewer system.

Your grandfathered downspout means that all rainwater from your house has to go through the sewage treatment regimen for your area. A second stormwater sewer system would usually just drain into a river because it contains only rainwater, and not blackwater sewage from households.

If your local building or code inspectors find out you added your new French drain output into the sewer, you will likely get fined as well as ordered to re-route your French drain to an acceptable discharge point.

Regulations are related to the U.S. Clean Waters Act of 1972 which trickles down to smaller municipalities and eventually to property owners.

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NO. you tie your downspouts into your French drain pipe, it fills full leaves, twigs, debris unless you have a filter. gutters can feed to the stone course to the drain but not directly

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