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Rick
Rick, General Contractor
Category: Home Improvement
Satisfied Customers: 13162
Experience:  Licensed construction supervisor with 35+ yrs. experience.
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I am installing a french drain in the basement purely as a

Resolved Question:

I am installing a french drain in the basement purely as a preventative measure. I don't have a water problem, and I have sealed the outside but since I am digging down a few inches anyway, I figured I would install a french drain. I have two questions.

The basement is 50 feet long by 20 feet wide. Sloping the french drain such a huge distance is a challenge as minimum grading is 0.5 so between the first part to the last part is 140 feet which would be 17+- inches in slope from the beginning to the end. Any ideas? And this gets to my second question. Since I really don't have any flooding problem, I don't want to connect it to a sump pump. I want to connect to the gutter that comes down. That would also solve my first problem as I have 4 gutters so the french drain slopes wouldn't be too bad.
Submitted: 9 months ago.
Category: Home Improvement
Expert:  Rick replied 9 months ago.

Rick :

Welcome, my name is XXXXX XXXXX X will do my best to help you with your issue

Ok, you only need 1/4" per foot not 1/2". I don't understand the last part of your question "I don't want to connect it to a sump pump. I want to connect to the gutter that comes down. That would also solve my first problem as I have 4 gutters so the french drain slopes wouldn't be too bad." Please explain.

Rick :

It sounds like you want to connect the down spouts from the roof to the french drain. If so where does all that water drain to?

Customer:

hi, considering I need 1/4' per foot so my perimeter of approximately 140 feet will require a trench depth of 2.91 feet for that last part of the french drain. Now I would have already started with a depth of 1 foot to begin my french drain so at the last part of the french drain where it reaches the pump, I would theoretically have a depth of 3.91 feet. Is there a concern that would be close to the foundation and far underneath the footer or is that no concern since it is only 6' wide and I will be cementing it right over.

I will explain the last part of my question : I don't want to connect the down spouts to my french drain. I want to connect my french drain into the pipe that the down spouts go. Remember that this is not a flood area whatsoever and I don't expect flooding, so I am not going to be overloading anything.

Rick :

As long as you don't undermine the footing and stay at least 3' from the footing should you trench below and parallel to it you should be fine. Also you can get away with 1/8" per foot since I assume you're running 4" pipe but the margin for error is smaller and you need to pat close attention to how you set your pipe.

Rick :

I have to leave for a while. I'll answer any follow ups when I return. If you don't have any more questions I'd appreciate positive feedback.

Customer:

ok, so just to make sure I completely understand. As long as there is packed soil of 3 inches in between the footing and my trench dig, I should be fine. Essentially, this means I will have my trench 15 inches from the basement wall - the footing juts out about a foot, and I will add another 3 inches before I begin my trench dig. By the end of the 140 feet, I will be about 3 feet below the footing (since my floor is at the level of the bottom of the footer) but my understanding from your response is that is fine as long as the trench is at least 3 inches parallel to the footer. And what are your thoughts about me not connecting it to a sump pump but rather to where the spouts run into

Rick :

3 feet not 3 inches, you need to leave 3' of undisturbed soil undisturbed near the footing except for where you will run you pipe under the footing and out of the basement. It's a lot less work and just as effective to run the drain into a sump pit. I'd install a pit. Also if you run it into a pit the pipe can even be laid level. It just shouldn't slope away from the pit at any point. You can locate your pit close to the edge of the footing. You don't need to maintain the 3' spacing but just for the pit.

Customer:

The basement width is 20'. Considering I have to be 3' from the edge of the footing, and the footing juts out from basement wall 1', I will be 4' from the wall on both sides leaving a space in between the trench of 12'. Will that be an effective french drain? And should I install a cactus board from wall to trench because of that. You wrote "Also if you run it into a pit the pipe can even be laid level" How can that be. The water still has to run to the sump pit, and if there is no grading, gravity won't get it there

Rick :

If you lay the pipe level the water will be at the same level throughout into the pit. This isn't like a plumbing drain where you need all the water to drain out. You just want to direct the water into the pit as the ground water level rises. If you lay the pipe level you won't have to go below the level footing so it can be run much closer to the foundation walls. This is how a perimeter drain in a basement is typically installed. And yes even if it's 4' inside the foundation walls it's still effective since you're eliminating ground water as it rises. You can go as close as 2' from the footing (if you go below the bottom of it) but you're not gaining anything. Since you've never had a problem I don't see the need for cactus board. Also the benefit of having a pit is that you can sweep water into the pit should you ever have a broken pipe or water heater leak.

Customer:

ok, I think I fully understand now. To recap - My new concrete floor will be level with the bottom of the footing. 3' horizontal from the footing I will be digging a trench around the entire perimeter that will be 12'' deep x 6'' wide. I will lay gravel at the bottom of the trench, lay landscaping cloth, lay 4'' pipe on top, surround with the landscaping cloth, lay more gravel on top, and place cement on top. The pipe will be level throughout. It will enter into a sump pit. I think its too complicated for me to run the sump pit pipe underneath the footing wall and out of the basement. Couldn't I just run the sump pit through the basement wall? What dimensions should the sump pit be?

Rick :

Just a few corrections; The sump pit doesn't drain out, the perimeter drain which can be laid level drains into the pit then you put a sump pump in the pit to pump any water out should it become necessary. (Best option) You dig your perimeter trench no lower than the bottom of the footing and right alongside it. Your process for the gravel and cloth is ok but no concrete on top except the finish floor. The bottom of your finish concrete floor is at least at the top of the footing. French drains are almost never used inside a basement. The rare exception is if you have a chronic ground water problem which you say you don't. Typical pit is 24" or 30" square lined with concrete block or you can by a prefab plastic sump.

Rick :

The bottom of a site made pit would be crushed stone with a block that you set your pump on

Customer:

Quote "You dig your perimeter trench no lower than the bottom of the footing and right alongside it."

Isn't that why we had our previous discussion earlier that I dig the trench 3' from the footing because I MUST go lower than the footing since my concrete floor is at the footing, and the french drain must be deeper than the floor level, and it goes 6 inches deeper than the floor level. I will buy the prefab

Rick :

When I was talking about staying 3' from the footing we were talking about going deeper than the bottom of the footing possibly a lot deeper. If you don't go deeper than the bottom of the footing then you don't need to stay 3' away. I'm not clear on the elevation of your slab. Since slabs typically are poured on top of the footing that is what I assumed in my last comment.

Customer:

the new floor won't be below footing, but the trench would be. The new slab is only 2'' above the bottom of the footing. This is how the room will look - basement wall, at the bottom of basement wall the footing extends appx 6'' from bottom of basement wall, then a drop of 5'' where the new floor begins. (yes, I know I lose basement space because I will obviously not jackhammer through the footing) So do I still need 3'?

Rick :

Yes, I would stay with the 3' to be safe. You can direct the drains into the pit and locate the pit up against the footing but only dig out enough for your pit when you are that close to the footing. A small isolated area next to the footing is ok.

Rick :

I have to leave for a while. I'll respond to any follow up questions when I get back. If you don't have any more questions I'd appreciate positive feedback.

Customer:

Something you said made me think I don't understand what a sump pit is. My understanding is that it is a pit in the ground that the water pools into and the pump then ejects the water up into the pipe that runs through the basement wall to the outside somewhere. I do intend to buy a prefab.

Rick :

Yes that's exactly what a sump pit is. BTW the 3' distance is based on the fact that I have no idea what type of soil you have. If it's hardpan (clay and shale) or clay you can trench to within a foot. If it's beach sand even 3' may not be enough.

Customer:

got it. Where do I go to analyze the soil, or can I determine myself

Rick :

As long as it isn't beach sand 3' is fine. If it's clay or hard pan it will be a real chore digging a trench since both are very tough to get a shovel into.

Rick :

You would need to hire a soil scientist to get a proper evaluation but that's not necessary or worth the expense in this case

Customer:

Thanks Rick, you have been really helpful. I have a follow up question that I hope you will answer since you already know my story. I will post.

Rick, General Contractor
Category: Home Improvement
Satisfied Customers: 13162
Experience: Licensed construction supervisor with 35+ yrs. experience.
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