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annie68164 03-04-2009 08:03 PM

opinions wanted on foundation trench sketch
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Our basement is leaking, is put in too deep and is on a flat lot. We can't grade correctly by adding dirt so we plan to take away dirt to create a grade that would direct water to the trench then fill in the "ditch" and trench with gravel using askthebuilder's simple trench plan. (24" deep trench with tile/gravel 4' away from house) I drew a sketch of what I'm thinking. The trench would run around the entire foundation and have an exit pipe to daylight. If anyone can see any flaws in the idea or something you would add or have tried personally fire away! Thanks

Scuba_Dave 03-04-2009 08:57 PM

Possibly under the gravel put plastic or something else?
As long as they are sloped correctly & the drain is to daylights I can't think of a problem

Are you sure its not from ground water coming up?
Is the daylight drain a large drop, storm sewer or?

Gary_602z 03-04-2009 09:13 PM

Make sure all downspouts for the eaves are draining away from the house.


Willie T 03-04-2009 10:10 PM

I wouldn't say "possibly" on the plastic, but definitely. And good, heavy plastic.

As your drawing shows it, think about it. You are really doing nothing, without plastic, to deter the water from continuing to simply absorb straight down the way it was before.

annie68164 03-05-2009 07:28 AM

Thanks for the plastic advice, I didn't really think of that but it makes perfect sense plus it'll keep weeds from popping up! As far as ground -water heck anything is possible but we are on a big hill (even though our lot is flat) so I would think logically it wouldn't be ground water. I am no expert but have read that in most cases what can appear as ground water is surface water that's just taking it's easiest route to any and every crack in your foundation- including the floor. Well, I will post when we complete this project and let everyone know how it went. After a few heavy rains I'll post if it kept water out. I'm sure there are plenty of leaky basements out there who can't afford to dig down to the footings and re-do everything. We are thinking with renting equip. and all else needed this project should be under $1,000 with us doing the labor.

jpsmith 03-05-2009 07:38 AM

This seems like a large project to undertake without being absolutely sure where the source of the water is. I suggest that you find out for certain whether your problem is surface water draining improperly or if it is ground water coming up. If it's ground water, your design will catch any of it coming laterally, but plenty could come from below, bypassing your gravel pit. I am near the top of a large hill, also, possibly the highest in my entire township, and I had groundwater seepage.

I put a similar trench on all below-grade sides of my house, except that the gravel was right up against the foundation:

This solved most of the problem, but I found that I still had some water coming up through the basement floor a day after a heavy rain. Ground water was coming up and "floating" the slab. To alleviate this, I had to open up a few paths in my slab and install 18" wide by 18" deep gravel pits with perforated drain pipe at the bottom that tie into the drain pipe alongside the foundation.

earthad1 03-05-2009 07:48 AM

This seems like the same type of issue I am having... Like if you look at his sketch, the crack I have in the foundation I posted in another thread ( would be right where his grade would begin.

So how can you diagnose if the water is surface water draining improperly or if it is ground water coming up? I thinking if its ground water coming up, and you dig a hole, you should hit water right?

jpsmith 03-05-2009 07:57 AM

I'm not an expert; I've only had to deal with this once. But one suggestion I have would be to dig a hold alongside your foundation. Keep digging until you hit water. If you make it to below the footer and it's still dry, then it's probably surface water. But you can't be sure just yet. cover the hole with a piece of plywood (to keep water out, as well as to keep kids or animals from falling in) and leave it for a few days. Check it every day or half-day to see if any water is pooling in the hole. If it stays bone-dry, it more than likely surface water. If there's water laying in there or if the bottom and sides are not drying out, it's likely ground water. Proper grading goes a long way to shedding surface water, because there's less resistance for the water to just run downhill away from the house than to penetrate the ground and foundation. Groundwater will move upward into your foundation due to pressure.

Willie T 03-05-2009 08:03 AM

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Some people forget that the pipe has to be down to at least the level of the footing.

jpsmith 03-05-2009 08:06 AM

+1 to what Willie said. You can sort of see in the pic I posted that my trench goes lower than the footing. My pipe is about where it is in his exaggerated illustration. This allowed me to collect the water from just a bit deeper, and also allowed the sub-slab pipes to have enough fall by the time they connected to the in-trench pipe.

Termite 03-05-2009 08:51 AM

I can't imagine how much gravel that this is going to take. I'm betting a couple end-dumps at least! $$$$$

If the problem is stormwater, this is a very workable solution to manage the runoff and water from the roof, and the depth of the trench isn't such a big deal and the plastic is very important. For groundwater, the depth of the trench is critical and the plastic might be counterproductive.

Another thing I'd stongly consider is a geotextile mesh fabric lining the trench before the gravel is put in, or at least a sock around the perforated pipe. Otherwise there's a good chance that the pipe system could slowly fill with sediment.

annie68164 03-05-2009 10:27 AM

The reason behind going only 24" deep on the trench is that at 24" you supposedly hit clay and water moves laterally at that point so no need to dig deeper. (This is according to askthebuilder's article) I do like that other poster's diagram and if we were doing a new basement (which we hope to do in about 5 years) we would do that exact thing. At this point we just want to keep the water out or at least the majority of it until we can jack up the house and put a new basement in. The trench would be 4-6 feet away from the foundation so should be able to capture all water because of the slope.

Willie T 03-05-2009 11:38 AM

I enjoy HGTV, and they have an entertaining little video on this subject HERE.

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