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Understanding What A French Drain Is


hausdok
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Watched the video & now I'm confused. I thought a French drain was installed on the inside walls of a basement so that they don't have to dig around the foundation. I see these quite often as it's a cheaper way to waterproof a basement. The bottom part of the basement wall is then covered with a type of Celotex/white plastic.

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Originally posted by Terence McCann

Watched the video & now I'm confused. I thought a French drain was installed on the inside walls of a basement so that they don't have to dig around the foundation. I see these quite often as it's cheaper way to water proof a basement. The bottom part of the basement wall is then covered with a type of Celotex/white plastic.

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It doesn't matter whether it's on the inside or the outside. After the house is built, it's often cheaper to install it on the inside.

The video doesn't mention the single most important detail about these systems though. The drain tile has to be located below the level of the footing if it's to be effective. (And of course not within 45 degrees below the footing.) I frequently see builders nest the tile on top of the footing and directly against the foundation wall.

Also, I prefer to see the filter fabric line the entire trench, not just laid on top.

- Jim Katen, Oregon

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I did an inspection for a hydrologist who also did EW work a few years back. He told me about a case he worked on where he demonstrated the huge difference in effectiveness between a french drain with only drain rock and one with perf pipe. He also laughed at using filter fabric (He was an old fart) . Oh well, personally I like the stuff.

Chris, Oregon

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Well, one more reason to hate HGTV (sorry...[:-boggled)

Perf pipe is fine, but drain pipe w/holes is better. Easier to pitch, easier to support, etc., etc. Honestly, even if the pipe is dead flat, enough water will flow to daylight or a sump.

The holes should face down; seems counterintuitive, but water doesn't percolate down into the pipe anway. (Does anyone think it does?!?)

Water saturates the soil and it looks for an area of equalized pressure to flow to. If the holes face down, the water seeps (up) into the pipe just fine, without the attendant deposition of soil & crud in the pipe.

If you're serious, you get filter sock, not fabric, and slide it onto the pipe; anyone that thinks filter sock/fabric is silly has clearly never been a hole doing the work, and they very clearly have never excavated pipe that's full of mud, crud, and roots.

HGTV get's on my nerves somtimes......[:-timebm]

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