Water pressure from slope causing crack and lean in foundation. Is a French drain the answer?

Question

We have a concrete basement foundation. It's the type with a retaining wall that can only be seen from inside the basement and a second outer wall on top of which the structure is built. The retaining wall has a crack and is leaning. We got a few quotes and the fix is.... not affordable at the moment.

One guy said that the best thing I can do immediately is dig a french drain on the outside of the house because the damage is caused by water pressure from the land sloping gradually in the direction of the house.

I thought that would be a simple google search and then I could get digging, but it turns out there are different views of what a french drain is and how it should be dug. I'm very confused.

I have a lot of questions, but first and foremost: Am I digging a trench that has no outlet, but is deeper than the foundation and catches the water from upslope and drains it beneath the foundation? Or am I digging a trench from the back yard to the front yard that drains the water into a drywell or something in the front yard?

I have to find a way to drain the gutter also since it currently drains into the front lawn from an above ground corrugated pipe. Can/should these problems be resolved together?

Photo 1: I pointed out the crack location and compromised wall in red. I pointed out the downspout with corrugated pipe in blue. There is a small slab foundation addition that I pointed it out in blue so as not to confuse anyone. I also pointed out in red the cracked wall for the stairwell which is due to the weight of the slab foundation (separate issue, but thought it might be relevant).

Photo 2: A close-up from a different angle.

Photo 3: showing the downspout and alleyway to the front yard.

I am appreciative of any advice at all. I don't have any experience with this kind of work and this house has too many problems for us to get professional help with all of them.

Couple of progress picks here. Not yet sure how I'll manage getting around the sewer pipe which is about a foot down. Also, found an old foundation wall, I'm going to have to pick up a sledge hammer to bash it to bits.

Answer 1

Water flows in the direction of least resistance. You need a french drain to keep the water off the wall.

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

If it comes up from a rising water table, it will enter the living space from below through the crack between the foundation wall and slab.

If it comes from the surrounding ground water, it COULD enter the living space through the wall, especially if the EXTERIOR side of the foundation wall is not sealed properly.

Either way the moisture will put pressure on the wall and could enter the basement. 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 basement slab.

To keep the subsurface water from putting pressure on the wall and 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. 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, the perf pipe needs to connect into a solid pipe and then extended over an embankment 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.

Answer 2

A French drain needs a location to drain to. Some drains are like a curtain in front of the house that extend down the side of the house to the lower area where the water can drain. If there is not a way to move the water or allow it to flow it would be useless. Some drains on flat ground end up in sumps so the water can be pumped out. Most of my homes have been in areas that had a slope and I have installed them to drain water coming down the hill to the house and causing foundation problems simple 3’ French drain with pipe in the bottom extending to the low side of the house eliminated my problems, other homes deeper drains were needed but that property had a huge slope. After the drain was added the problems were fixes at that place. It looks like you have a fair drop to the property behind yours as the roof level looks to be almost at your ground level so you have 5-6’ of slope to work with if that is your yard, put the drain in the front drain to a low side or if level side to side both sides to the lower area in back, this should help if surface water coming down is the issue and this can cause problems with only a few feet of slope. The good news a small slope of only a couple of feet usually only requires a trench 18-24” deep, I find steep properties require deeper trenches , my last home had 5-1/2’ deep ~10’ in front of the house and that set of drains below the house we had to bring in more rock as it flowed like a fire hose ok no pressure but but the 4” pipe was flowing almost completely full of water, flowing onto rock we dumped. The drain helped in several areas of that property.

Answer 3

1. Rain drains - solid pipe that takes the rain to a storm sewer.
2. Perimeter drains - 4" perforated pvc pipe installed at or slightly above the footing of the foundation. These either flow to a sump well and then to a storm drain or can be directed into a sump well with a sump pump that pumps this water into either the storm drain or the sewer.
3. Hydrostatic pressure on foundation wall - addressed with waterproofing spray, dimple board (delta ms is popular) and drain rock or combination.
4. Slope the grade away from the house to minimize load on your water management system. Ideally grade should be 6" lower than any wood so in your case it looks like you'd want to remove grade from the rest of the yard as the grade is close to your siding already.

I'd address 1 first, then 4, then 3 on the affected section of wall.

2 is the most difficult as you have to do a lot of digging. Perimeter drain pipe doesn't need a lot of slope and is often installed almost flat so you could probably do one section of the house at a time once you figure out where you are taking the water (storm sump, powered sump pit, etc).