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Right now I have a sump pump and have for years. I believe that pump has been there at least two decades, works fine. But, I thought I'd try and fix the water leaking. If I put a French Drain in the crawlspace, I have no where to drain it except a sump pump. I already have that.

If I put a French Drain on the outside of the house, next to the house, will that work, or does it have to be in the crawlspace?

I have seen water come in through some of the cinder blocks before, or under them, I do not remember.

How far down do I dig? To where the cinder block meets the cement footing?

The crawlspace is already low, so the outside will require more digging. My yard is sloped and the water will use gravity to a County "rain drain." There are no neighbors, so I don't have to worry about that. Other than this, keeping gutters cleaned is all I can do.

  • While a french drain on the outside may help move the water away from the foundation it does NOT address the failure of the foundation and that should be addressed. – Alaska Man Jun 14 '17 at 19:03
  • Or a bit farther away from the house. The objective is to lower the water table around the house. – Harper - Reinstate Monica Jun 14 '17 at 19:17
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Cinder blocks are quite porous. To keep a basement or crawl space dry means keeping subterranean water (water table) and surface water off the foundation wall.

Where I live we have a water table at about -24". The only way we can keep basements or crawl spaces dry is to: 1) install a 4"-6" perf pipe about 6"-8" BELOW the basement slab or crawl space, 2) encapsulate the pipe in drainrock (round 3" minus rock without fines), 3) extending the drainrock to within 6" or so of the ground surface so any water trying to "build-up" against the wall, will be drained down to the perp pipe and carried away, and 4) waterproof (coat) the foundation wall to keep surface water from penetrating the wall.

Sometimes we'll wrap the drainrock with filter fabric, depending on the soil. Make sure the perf pipe extends to a drainage swale and we don't connect roof drains into the perf pipe...we extend the roof drains (in a solid pipe) to a drainage swale too. We also add a 1/2" protection board (inert cement board) on top of the wall coating, so when the drainrocks are dumped in, they don't damage the coating.

This system works, unless you are located next to a large hill where the water table "up the mountain" can "push" pressure on the water table under your house. Then, it will cause the water table to rise UNDER the house. To fix this, we run french drains about 10' on center under the house...very expensive.

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  • I would just add if you don't room for a drainage swale many houses in areas of high water tables actually drain into the sump inside the house basement and are then pumped far away from the house. This necessitates a sump pump that is on a UPS so it can still pump after power loss. – ArchonOSX Jun 15 '17 at 9:34

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