Internal/Foundation French Drain in Crawlspace


Old 05-04-17, 02:44 PM
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Internal/Foundation French Drain in Crawlspace

Hi everyone,

We are in the process of building a french drain in our crawlspace, as we've had issues with water pooling in several locations. We have it designed for the most part, with one exception. We are not sure how to build the transition from the trench part of it (crushed stone, geotextile fabric, perforated pipe) to the solid pipe part that will drain the water (we have a solid pipe connected to the foundation drain that will carry it to the street). Of course, we'll attach the perforated pipe to the solid one using a fitting, but from what I hear, most of the water actually travels through the trench/stone, and not through the actual pipe. Our concern is that while the water will be transferred from the perforated pipe to the solid one, what will happen with all of the water in the trench? Will it just seep into the soil where it ends? How do we funnel it so it will drain? We've also considered putting in a catch basin at the transition point, but that still won't solve the problem of how to move the water from the actual bottom of the trench into a discharge pipe.

Any ideas would be much appreciated.

Also, just FYI...there will not be a sump pump, all of the water will be moved using gravity.
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Old 05-04-17, 04:07 PM
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Water will take the path of least resistance. If designed and built properly the water the water will find it easier to move in a nice unobstructed pipe. If the water moves through the stone in your trench when it gets to the end of the trench it will again take the path of least resistance. It could flow into the pipe or rise/pool up depending on how you've built your system.

Many people misunderstand how it works and will place perforated pipe with the holes facing up thinking they want the solid bottom to hold the water in. Not thinking of how the water is supposed to get into the pipe.
Old 05-04-17, 04:10 PM
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your perforated pipe is at the bottom of the trench and the trench slopes toward the solid pipe.

the perforated pipe allows the water to easily flow out.

yes there will be some water in the trench that soaks into the ground which is not a problem, the excess will flow away.
Old 05-04-17, 04:45 PM
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Thanks for the input.

Marq, from what we've read, there should be 2-3 inches of gravel below the pipe, so there will be 2-3 inches of water (well, less, because of limited space between the stone) below the pipe.

Pilot Dane, sounds like you're also suggesting not doing anything at the end of the trench? Just letting the water sort of pool in the bottom? I'm sure not all of the water will actually get up and into the pipe.
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