French Drain for a home on a hillside
Category: Family and Home > Home
Asked by: neilgandhi-ga
List Price: $20.00
15 Jun 2006 18:54 PDT
Expires: 20 Jun 2006 17:33 PDT
Question ID: 738568
I own a house that is situated in front of a slope. The part of the slope that is directly behind my house is moderate (rises about 15-20 feet over about 30-40 feet) behind that slope, there is a heavy slope (rises about 40 feet over 40 feet). When I bought the home, there was a room filled with mud that ran across the length of the house which faced the hillside. The mud in this room started at the wall facing the hillside at the ground level of the dirt on the other side of the wall. The mud in the room ended at the ground level of the bottom story of the house. Basically, I think this room was designed to take all the water that entered the room and divert it under the house. Anyhow, since then, we have remodeled the house to take advantage of the space that the mud-filled room took up and added three rooms to our home. The problem now is that our contractor ditched the job and didnt install the linear french drain that was supposed to go in the back (which is the side of the house facing the hillside). We have since gotten estimates and have decided that it was too expensive to get done and that we would have to do it ourselves. We have started digging, but I'm trying to figure it all out. I've looked online but have found that this particular case is very unique. The ground level of the mud outside is about 6 feet above the ground level of the three new rooms and I don't know how deep I should dig, how far away from the wall I should dig, what kind of rocks to backfill the trench with and such. My plan at the moment is to dig about 6-7' down right against the side of the house (exposing the concrete); just enough to get to the ground level of the bottom story of the home. I want to make sure I grade the trench about 1" for every 10' and cover the side of the house with a thick plastic. Then I plan to spread a 1" layer of sand (as an elastic cushion for the pipe) and lay the filter-fabric covered 4" perforated pipe. After that, I want to fill 2-3' of the trench with 3/4" gravel, and the rest with 2" pebbles. On the top of the 2" pebbles, I want to put cobblestones that are stacked on top of each other so that they have a slope that is down and away from the house. My question is if I am attacking this problem correctly. If I am not please help me correct any mistakes that I am making. I have heard a lot of people saying that I don't need to dig that deep. The people that gave me an estimate though said that they were going to dig 1' below the footing of the house. My concern for me to dig that deep is that the house will become unstable. Please address those concerns as well.
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Re: French Drain for a home on a hillside
From: daniel2d-ga on 15 Jun 2006 22:21 PDT
Hire an engineer that can examine the site and tell you exactly what to do.
Re: French Drain for a home on a hillside
From: eiffel-ga on 16 Jun 2006 06:39 PDT
Hi neilgandhi-ga, I think you have to have someone come on-site. Even if you are going to do all the work, get an engineer to specify it. One problem you may find is that the engineer may be over-cautious and over-specify. After all, they'd rather have a customer dig much more than they need to, than to have a customer complaining that it doesn't work! But it's really the only option. Regarding how deep to dig: it's a law of diminishing returns. You can get a relatively big benefit from a relatively shallow French Drain, yet depending on your local conditions (soil type, foundation type, rainfall level, catchment area etc) you may need more than that. Another option that might help is a V-shaped drain uphill of the house, to divert some of the water away before it even gets to the house. It probably won't avoid the need for a French Drain, but it might avoid the need for such a deep French Drain. But again, without going to the site, it's impossible to say.
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