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I live in a local minimum for my neighborhood, and in fact my house is built on the banks of a stormwater drainage ditch. Most of the rainwater from the road is collected by stormwater drains and fed directly into the ditch via a pipe, but the water that falls directly on our own and our neighbors' yards still has to make its way around (or through) our house to get to the ditch.

The house was built in 1920 and originally had a limestone wall foundation, parts of which have been replaced over the years - mostly with CMUs on a poured footer.

At the lowest end of the yard is the entrance to our crawl space. It appears that the foundation wall that runs along the slope (perpendicular to the ditch) was replaced with CMUs at some point, but it has another interesting feature - a large L-shaped concrete pour:

L-shaped footer

My guess is that they temporarily supported the house on the smaller pour+embedded deck block you see immediately to the right while they poured this footer. In fact when we bought the house there were still some posts standing on those blocks, though they were loose and no longer acting as support.

During the wetter months (winter/spring), this area is quite muddy (though no standing pools of water usually). My theory is that the footer is too shallow, so water is migrating under it and wetting the basement. The fact that there is a tree root growing through that space seems to give further credit to this theory.

As you can see, inside the crawl space the terrain follows the natural slope of the yard. But on the outside, a retaining wall made of railroad ties holds a large amount of soil up against the outside of the foundation, rather than letting the yard slope down naturally towards the ditch at the bottom:

Foundation wall running along slope

My thought is that the retained soil on the outside acts as a sponge, and then slowly releases this moisture into the crawl space. Would making the footer deeper help keep the water out? If so, what is the best way to do this? My current plan is to reinstall the temporary supports, excavate the soil from around and under most of the footer, add a rebar grid (or cages) and build a plywood form, and then pour concrete. The hope is that the footer will support itself during this process with the "leg" at the lower end, and the unexcavated soil at the upper end.

Or should I simply remove the railroad ties and excavate the retained soil on the outside of the house, restoring the natural grade of the yard? I have considered replacing it with a deck on posts in this case.

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Water flows in the direction of least resistance.

Moisture is either coming up from below (a rising water table) or its coming from the surrounding ground water in the saturated soil, or both.

If it comes up from a rising water table, it will enter the crawl space from below.

If it comes from the surrounding ground water, it COULD enter the crawl space through the wall, especially if the EXTERIOR side of the foundation wall is not sealed properly, especially if your wood retaining wall is keeping dirt against the foundation wall.

Either way the moisture enters the crawl space and it will need to be collected AND disposed. NEVER install perf pipe around your house and under your footings. This can cause settlement. Removing undisturbed soil to install drainrock and a perf pipe, it will cause settlement.

I think the best way to collect it is on the exterior side of the foundation wall in drainrock and a perf pipe laid 6”-8” below the interior crawl space dirt, but no lower than the bottom of the footing.

To keep the subsurface water from seeping through the wall, I recommend installing a moisture barrier on the exterior side of the foundation wall and install a 2” thick plastic mesh on the wall to allow water to flow down to the perf pipe. (Water flows in the direction of least resistance. You want water to flow down the wall not lay against the wall.) If dirt is allowed to be backfilled against the wall, the dirt could hold the moisture giving it a chance to seep through the wall.

Once collected it needs to be disposed by extending a solid pipe over an embankment, to your drain ditch or in a collection well and pumped away.

This may be the most expensive method of solving the problem, but it’s sure to work.

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  • Thanks! I’m doing all the work myself so the main cost would be materials and my time. Do you think it’s a bad idea to try to pour concrete under the L footer as well? That portion of the house is fairly lightweight, only a single story with a simple shed roof and wooden framing+drywall. – alexw Apr 26 at 15:34
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    The footing and foundation wall has obviously been reinforced in the past. I would not disturb the “bearing soil” under the footing. I’d rely on perf pipes installed in a drainrock envelope AND a 2” filter on the wall to keep the hydrostatic pressure off the concrete wall leading down to a new perf pipe AT the footing, but not below it. – Lee Sam Apr 26 at 19:10
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    I had a similar crawl space, the water came up from the soil . Putting down a good plastic sheet over the soil and cover it with pea gravel to make the most improvement. – blacksmith37 Apr 26 at 20:13
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    +1 for the perf pipe solution, and placement described here. But make sure the pipe lead somewhere and you can properly dispose of the water. In your case, the slopes of the yard should makes things easier, no drainage pit and pump required. – Louis Charette Apr 27 at 18:37
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    On the RR ties, make sure the water can flow trough them. You don't want water to accumulate behind them (same goes for any retaining wall). For the space under the footing, I'm with @LeeSam, don't disturb the “bearing soil” under it. There are some solutions to inject cement based or urethane based product under it (I've seen it done for concrete slabs, will probably work for footers too). But only do it if you start to notice movements. Otherwise, make sure the void doesn't get bigger and it should be fine. – Louis Charette Apr 27 at 18:41
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Doesn't matter how deep the footer is. It's about the water table. You could get a drill rig and redi-mix plant out there and make the footer 50' deeper using a secant cutoff wall. The water table wouldn't care, it would go under it.

The way you fix this is by lowering the local water table using French or Buckeye drains. Fortunately your property is on a grade, and you have the very, very convenient drainage ditch as an appropriate place to redirect the water without kicking the problem down to your neighbors.

So I would lay such drains around your house, setback (distant) enough from the house , that there's no risk of destabilizing your foundation, and what I mean by "set back" is far away from the house - e.g. if it's 4' deep make sure it doesn't get within 8' of the house. It doesn't help to hug the house, and risks undercutting the foundation, so there's no reason to do it. Given that reasonable setback, you can go as deep as your foundation footing or a bit deeper (depending on practicalities, you don't want it so low that drainage ditch water regularly backflows).

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  • Why would you recommend laying drains, “around your house ...a bit deeper than the foundation “? – Lee Sam Apr 26 at 1:11
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    I would suggest a French drain above the house and down 1 side not normally a water table issue with a good slope but surface water movement we see this regularly in Oregon I had drains on my last property that at peak filled a 4” drain , moving the water around the drive, house and shop eliminated our issues. – Ed Beal Apr 26 at 3:27
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    No geotechnical engineer would ever recommend installing a perf pipe “a bit deeper than the footing” for fear of settlement. – Lee Sam Apr 26 at 14:27
  • I excavated and installed a French drain last spring just uphill of the house, but it’s unclear how much that has helped with this (downhill) part of the house. My main goal with that was to relieve hydrostatic pressure on the uphill wall, and generally dry out the soil to prevent further rot. – alexw Apr 26 at 15:40
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    Despite the discussions about "deeper than the foundation", I agree with Harper that lowering the water table around the foundation, or keeping it from building up is the right approach. Even if you have some flow or percolation through the soil, the hydrostatic pressure from a column of water in the ground will force water under a footer and up into the dirt crawl space or basement. Basically, you need to keep the ground water from ever reaching the bottom of the footer. – SteveSh Apr 26 at 16:58

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