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sonicsmooth 02-02-2011 03:34 PM

Interior French Drain
I need to install interior french drain in basement, without sump pump, so gravity fed into sewer.

General contractor who has offered to do the work says I need a catch basin before going into sewer, which means a giant 4-5' deep hole outside, with an extender so I have access to it from the lawn.

Separate plumber says no, only exterior drains need catch basin, but the interior one can tie directly into the sewer if it's done inside the house, without catch basin.

So do I need a catch basin?

Can anyone definitively answer this? I looked for the exact plumbing code for my city (Seattle), but it appears only available for purchase, not online.


LateralConcepts 02-02-2011 03:51 PM

In most jurisdictions you're not allowed to tie a french drain (ground water) into the sewer. It would need to be routed away from the house or to the cities storm water system.

I don't know the codes in Seattle, but I'm guessing Seattle has a quite sophisticated storm water system due to the amount of annual rainfall.

AllanJ 02-02-2011 06:02 PM

All the same features used with an exterior French drain also work with an interior French drain and vice versa.

However some features are more convenient for interior and some are more convenient for exterior. For example if you have an exterior French drain but want your sump pump to be inside then you must burrow under the foundation footing (okay for one spot alog the foundation, for one pipe) so the water can get to the interior pit.

I don't see the purpose of a catch basin other than being the equivalent of the sump pump pit but porous and more correctly being a dry well. Meanwhile if it does not have a sump pump of its own then it is liable to overflow.

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