How far from the foundation and how deep should a French drain be


My wife and I bought a house recently but sadley the rainy season has come and I noticed a bad smell coming from the crawlspace I went under neath and found standing water about a inch deep running along two walls of the house.

The rain water is sitting on one side of the house and will take a few days to actually drain away/ evaporate so I've decided to install a French drain to help it run.

I was going to use 4in corrugated piping and hook the gutter system into it

And I just had a few questions

How far away from the foundation should I be?

With the soil being a majority sand should I dig shallow or deep? Or deep with a lot of stone on top?

And with the soil be majority sand should I use small stone, or large?

Thanks in advance for any advise you guys have!

Best Answer


Since the water generally comes from outside the home's footprint, drain tile is usually installed along the footing (inside, outside, or both, depending on the situation). Whether you need interior circuits in your case is uncertain.


You don't want your drain to work harder than necessary, so it shouldn't be deeper than necessary. They're typically installed slightly below the underside of a basement slab, for example, or just below the top of the footing along which it resides.

Drainage Media

Clean (washed) rock is important, but size isn't so critical. More critical is that you protect against silting. Fabric either wrapped directly around the pipe or laid over the washed rock medium helps prevent the surrounding soil from infiltrating the pipe and clogging it over time.