French Drain or Regrade or Both?

vandyalumJuly 9, 2014

Good morning. I am purchasing a house and due to water leaking into one sideof the cellar during hard rains, the owner agreed to install a french drain and/or regrade around that side of the property. Yesterday, the contractor installed the french drain. You can see where it was installed per the photo. My soon-to-be house is on the left.

Here are my questions:

(1) As you can see, the houses are closely set together. Though the contractor installed the french drain, he did not regrade. Given the amount of land available and the height of the foundation wall, is it possible for him to regrade?

(2) Even if possible, given the existence of the drain, is regrading necessary?

(3) Separately, as you can see from the photo it appears that he connected the downspout to the drainage system. Is this advisable?

Thank you.

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yardvaark

Describe what a "french drain" is. What do you now have? I'm sure it is a "joke" to help sell a house.

The surface grading obviously drains all the water toward your house. Only surface re-grading can fix this. there should be a swale running the length of the center of this space. But it's such a tight space a curb and elevation change would be useful. And a hard paved gutter would be useful. The water would drain toward the photographer and beyond, but we can't see that so wouldn't know if anything terrible is going to happen with water as it leaves the two houses.

    Bookmark   July 9, 2014 at 8:48PM
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vandyalum

What was installed is a french drain, aka a perimeter drain. Basically, the contractor dug a trench along the perimeter of the house, presumably laid down gravel, put in a perforated pipe, laid down more gravel on top, filled it back with dirt.

Here's the problem with the swale. It would certainly need to encompass a portion of the property that is arguably not mine. And I think to do it properly, earth would need to be removed from the neighbor's property, and I'm not certain the adjacent land owner is keen to have this done. Nonetheless, the photographer (me) is standing at the sidewalk. Nothing terrible will happen with water as it leaves.

Can you explain further what you mean by a curb and elevation change? I presume you would put the paved gutter in the swale, or somewhere else?

Thanks!

This post was edited by vandyalum on Wed, Jul 9, 14 at 22:34

    Bookmark   July 9, 2014 at 10:30PM
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pls8xx

You mention two terms, french drain and perimeter drain. A house perimeter drain is built at a level below the basement floor elevation. In your case this would be about 8 feet deep. A proper and working perimeter drain keeps the water table outside the foundation walls below the basement floor level. This prevents excessive hydrological pressure on the foundation wall and deters water leaks into the basement.

A shallow french drain can de-water some soil types above the bottom level of the pipe. But the soil below that level usually is wetter than without the drain. Such drains along foundation walls often lead to water problems in basements or make existing problems worse.

    Bookmark   July 10, 2014 at 8:29AM
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vandyalum

Ok, nomenclature aside, the contractor installed what I described above. If a perimeter drain is technically what you describe, then I'm certain that wasn't installed since, I don't have a basement. I have a crawlspace in the front and back of the house and a 10x15 cellar in the middle.

What I really need to know is (1)-(3) in the original post. After the owner (who, by the way, is a contractor) suggested that he would install a french drain (and arguably regrade), I had a a few contractors come out to look at the house, and they all independently suggested a french drain. I'm not saying that they are all right, and perhaps the answer is not a french drain, but for the time being, the french drain - or whatever you want to call it - is installed.

    Bookmark   July 10, 2014 at 8:57AM
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pls8xx

(1) As you can see, the houses are closely set together. Though the contractor installed the french drain, he did not regrade. Given the amount of land available and the height of the foundation wall, is it possible for him to regrade?

Yes (see Yardvaark's suggestions). IMO, the french drain should be removed before regrading and all near surface backfill used in the area should have low permeability. This may not solve the water problem in the cellar but is the first step before much more expensive things are done.

(2) Even if possible, given the existence of the drain, is regrading necessary?

Yes.

(3) Separately, as you can see from the photo it appears that he connected the downspout to the drainage system. Is this advisable?

No. Roof drains should not be connected to subsurface drains. Roof water should be routed through solid, not perforated pipe, to a suitable discharge point.

    Bookmark   July 10, 2014 at 10:12AM
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yardvaark

"Basically, the contractor dug a trench ... filled it back with dirt." It is a PERIMETER drain which COLLECTS water. But, Vandy, you failed to say TO WHERE the water drains ...?? (In my world, the term "french," insomuch as it is applied to drains, describes to where -- what kind of structure -- the water drains.) (Which was why I asked about it.)

The cellar is located like a basement so the same principles would apply.

The perimeter drain collects water that has already entered the soil in an effort to give it a path to somewhere non-harmful BEFORE it enters the lower parts of a house. It's a "fail safe" device that still keeps things safe after something else before it has failed. In this case that "something else before it" is GRADING. The grade should be such that it channels water AWAY from the building and guides it to places where it cannot harm things (... to paved areas, curbs and gutters, streets, gullies, rivers, etc.) In the picture above, it is clear that the grade does NOT channel water AWAY FROM the house at the left. So yes, in spite of the fact that a perimeter drain has been installed, proper grading is still essential. The drain should be forced to take care of only what has escaped the the surface remedy ... grading.

The space between the houses is tight, but there IS grade, so of course, it's possible to regrade. As I mentioned previously, since the space is tight, it would likely be better if a structure such as a curb (which is like a mini-retaining wall and allows grade change) and possibly a paved trough is installed. The objective would be to get surface water out of this tight space as quickly as possible. Obviously, if the area is handling minimal amounts of water, it's not as critical as if it was handling massive amounts. We don't have knowledge of where water is coming from and how much there is or is likely to be. Nor can we solve without knowledge of where responsibilities begin and end (lot line locations.)

Personally, because it adds complexity (can possibly cause future problems and fail) I don't like underground piping if it is at all possible to avoid. (I am not speaking of the COLLECTOR DRAIN here.) One would know if the downspout that's running into the underground pipe is likely to be a problem only if one knows its entire path to the discharge point.

Suppose you had a roof that was leaking because two surfaces came together in the form of a "V." (The leak being at the bottom of the "V.") This would be a built-in design flaw and is in fact, essentially the condition of the grade that you, OP, are faced with. Your title question is essentially asking if it is sufficient to collect the water after it has leaked in at the bottom of the "V," or if the "V" should be reshaped into something that sheds water instead (regrading.) While collecting water after it has leaked in is useful, the preferred method is stopping as much water from leaking in, as is possible.

This post was edited by Yardvaark on Thu, Jul 10, 14 at 11:04

    Bookmark   July 10, 2014 at 10:53AM
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Allen456(8)

Where is the gas line that serves that meter in the back?

If you're going to do any digging, make sure you locate the utilities.

    Bookmark   July 10, 2014 at 11:08AM
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vandyalum

A quick follow-up for clarification:

The french drain in and of itself has failed, given that after hard rains last night the cellar leaks as it did before the drain was installed. Whether it failed because it was not properly installed or because of the grading is unknown, though it's likely the grading or a combo of both. In any event, regrading is essential.

PLS8XX, you suggested that the drain needs to be removed before regrading. Can you explain why? Is it not possible to leave the drain in and regrade on top of it? I'm just trying to arm myself with information.

Thanks!!!

    Bookmark   July 14, 2014 at 9:34AM
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pls8xx

I suggested the removal of the french drain because it's common for the soil above a french drain to be dryer, but the soil below the drain pipe is often wetter, which is not good along a basement.

You may very well get by with leaving the drain in place if all of the surface soil in the area is of low permeability. It will help if part of the area is covered with a concrete gutter as suggested by yardvaark. Make sure you disconnect the drain from the pipe carrying the roof water.

    Bookmark   July 14, 2014 at 12:20PM
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vandyalum

All the suggestions on here have been so helpful.

One final (hopefully) question. The drain does not work. Meaning, there is no water flowing out of it. After the first rain, I had a suspicion this might be the case, but I didn't know for sure. After a few dry days, I tested the drain by flooding the area. Water leaked into the cellar. No water flowed out of the end of the drain.

Presuming the drain was properly installed, are there any other reasons? Perhaps the water is disappating into the soil too quicly?

    Bookmark   July 18, 2014 at 2:36PM
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