Foundation drainage advice - french drain or not?

3 years ago

last modified: 3 years ago

We recently discovered leaks into our finished basement. Not gushing water, but enough seeping in to cause mildew smell, mold on the back of drywall and rot some stud wall sill plates.

At first we thought it was a leaky foundation, so we demolished interior walls and excavated an 18" wide trench on the outside. We saw the primary issue was our next door neighbor’s yard, where he had soil and big bamboo plants against and above our foundation and against exposed wood (this is an old house). Holes from roots and rot allowed water in. These plants and soil have been removed. To keep the lower soil grade against our foundation, we’ll maintain that trench between and build retaining wall on the other side of the trench to hold up the neighbor’s higher grade.

We got a professional opinion that there is no water entering through the foundation or floor, so, theoretically, problem solved. The question is - how we backfill the trench to encourage proper ongoing drainage? French drain, soil, gravel, rock, something else?

Attached are some pictures showing the situation. The plastic shown in the later two pictures is temporary covering for the exposed foundation, which is shown in the first picture.

Some contractors insist we need a $20K-$30K french drain system. Others say we can just waterproof the exterior foundation wall since we have access, then backfill the trench (both much less expensive).

It doesn’t rain a lot here, except during winter, when every few years we get rain heavy enough cause sewer backups. In our case, water runs downhill alongside/parallel to our foundation, not towards. Roof gutter downspouts overhead are connected to city drain pipes. Soil is pretty packed with a lot of clay, but it does drain.

My thought is backfill that trench with the drainage gravel they use over French drain, and keep soil off of it. My concern with that is that water spilling down the hill and over retaining walls could overwhelm the trench, which would drain more quickly than the soil.

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Comments (14)

PRO
GN Builders L.L.C
3 years ago
You can probably do something like this as you would do basic drainage just make sure it has a place to drain the water to keep away from the foundation.
DC
Original Author
3 years ago
We're trying to avoid a French drain - we don't have daylight to drain it to, and it will cost a fortune to install, connect to drain pipe, sump pump, etc.
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Unless you're driving over it, black corrogated pipe will be fine. You can use a combo here if you must cross a driving path, putting solid piping under the place with the biggest load, and lighter stuff elsewhere. The black stuff is also better if you must do a curve. But, ya know, French drains (at least the ones I'm familiar with and have installed) don't actually have pipe, just coarse rubble. They are basically rubble-filled trenches. Trenches with pipes are called tile lines (in the old days the pipes were terracotta). However, if you are tying your down spouts in, then I'd definitely use pipe on the whole length as that amount of water over short periods might overwhelm a rubble pathway. Another thing, is that I wouldn't delay getting those trenches backfilled. I'm not sure what your climate is, but you wouldn't want spring run-off to enlarge the ditches and threaten the stability of the earth close to your foundation. And I wasn't sure if your question about the drainage related to two buildings (barn and house) or if you were jocularly referring to your house as a barn? Have you thought of installing a good-quality vapor barrier directly on the soil under the buildings to interupt the upward migration of soil moisture to protect the wood components? Molly~
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Basement stairwells usually have a seperate drain to the sump as do each run of tile from the perimeter of the building. There is filter cloth which is used to line drainage systems of the type you describe. It was not always used. If the cloth was not used, silt from the backfill and years of soaking rain will infiltrate the stone surrounding the tile and eventually the tile itself. Settlement will also cause dips in the pipe itself which will cause some water to "belly UP". Some of this silt will serve to level out those bellies and allow the water to drain. So a little silt at these points is ok. Rather than throw the most dire probelms at you and try to scare you with the more complex and worse case scenarios, I'll stick with the simplest and most affordable action. I think this would apply to your situation for a couple of reasons. One, the house is 24 years old and if it were a "really bad" problem, you would be complaining of flooding, not slow water drainage. Two, I've seen the problem you describe many times and the easy fix has always worked, with the soil composition you've described. If you had clay soil, it would have been much more complex. In my experience, I think the drain tile from the walk out stairway to the pump has a 24 year buildup of silt in it. There are a number of ways to clear it. It will be a little time consuming (a few hours) but it is a DYI job and will be is as good as new when you're finished. Remove the drain screen and put a garden hose without a nozzel into the cellar drain and let water run into it at a rate it will readily drain (you will increase rate as you clear the silt). At the sump end, insert another garden hose with a nozzel into the pipe where the water drains from. The nozzel should be the single cylinder type and locked into the heavy spray position. Start inserting the hose further into the pipe, the further the better, while running the water at full pressure. Silt will start washing out. As the flow increase, increase the water pressure to the outside hose. If the outside hose can easily be inserted further into the drain, do it. Keep working it this way until the watre runs clear. This method will keep you from clogging the pipe with silt. I don't recommend you do this but, once complete, you could put a ping pong ball in one end and a shop vac at the other and the ball would pop right through. Now how did I know that?
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worthy
3 years ago
Waterproof the foundation. Which is not just a quick spritz of asphalt spray. Then add the French drain as shown above along at least the excavated portion shown. It doesn't have to be tied into a drain, sump pump etc. It can simply drain under your lawn. Impossible to say where from the pics you show. The $20K-$30K quotes seem absurd.
PRO
GN Builders L.L.C
3 years ago
If you hire someone to do it, you right it will cost you, if you doing this yourself you will save a lot of money and from the picture, it looks like that hardest part of the job already done.

Good luck
DC
Original Author
3 years ago
@worthy This is San Francisco, labor rates here are insane.
worthy
3 years ago
Flowers in the hair replaced by Benjamins!

(Construction rates 43% higher than the US national average.)
pls8xx
3 years ago
I wouldn't put a french drain there even if someone offered to do it for free. A short DIY retaining wall might be beneficial if it supported a grading that gave surface water an exit.
DC
Original Author
3 years ago
@pls8xx what would you fill the trench with after the retaining wall?
DC
Original Author
3 years ago
@worthy when you say it doesn't need to be tied into the drain, do you mean just have the pipe there open ended?
pls8xx
3 years ago
@DC

Water runs down hill. It's best to keep the water at a high elevation, then you are in a better position to find a lower place to discharge the water. I'm assuming the natural drainage from your neighbor is toward your house on the side in the photos. In that case you will need to try to route the water around the house.

Backfill the trench with non-permeable soil compacted so that water stays on the surface. The suggestion to waterproof the foundation was a good one. See if you can grade the soil next to the house so there is a downward slope to carry the water around the corner of the house. A retaining wall may or not aid you in getting the correct grading.

If you need a wall less than 2ft tall, consider poured-in-place concrete. Cheaper and less skill needed for DIY.
worthy
3 years ago
last modified: 3 years ago
do you mean just have the pipe there open ended?

No, run it under sod, into a planting bed, whatever you have. We can't tell from the photos. As for re-filling with non-permeable soil, even concrete will end up channeling runoff toward the foundation, and hence into the basement. I've owned and repaired homes where the concrete-happy former owners tried just that.
fourpawsonetail
3 years ago
I really hate to burst bubbles but you've got a major problem here that if not dealt with properly is only going to get worse and costly. Trying to correct this yourself probably wont work unless you have extensive experience dealing with what you describe.

Look at it this way, you already have a mold problem, it's going to get worse if not properly dealt with. You also have what appears to be wood rotting issues along with structure issues.

I'm not a professional in this department but I've had tons of expensive experience with this issue (tried french drain, didn't work). should have bitten the bullet and installed a sump pump. My lesson learned is not to skimp trying to correct a problem like this, it only winds up costing more in the end

good luck!
Embothrium
3 years ago
last modified: 3 years ago
Service provider labor charges long ago became a profit builder, with employee compensation often being a fraction of per hour labor rates customers are billed. For instance with one position I have held myself my hourly pay was 1/6th what the operator was collecting for my involvement.

Estimates, quotes and actual work performed recently here at my new place have given me the impression figuring hundreds per hour for labor has become standard in activity areas like construction, heating and plumbing. In one case the line for carpentry work on a construction estimate had this costed out at over $4,000 per hour. I hope this was a mistake, but never asked.
pls8xx
3 years ago
Nothing new here. Labor cost are outrageous. Over 50 years ago my new wife said something needed repair, should she call a repairman. And I said NO! absolutely not. If I can't fix it, it ain't broke.

Foundation drainage advice - french drain or not?

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GN Builders L.L.C

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Foundation drainage advice - french drain or not?

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