Flooding basement - what do you know about French Drains?

42 Replies

My neighbor's basement is flooding after some pretty heavy rain over the past week. They have called a basement guy out, who would solve the problem by jackhammering up the cement floor in the basement, digging a trench and installing a French Drain that goes into a sump. Has anyone done this before? Did you have success? Do you know the benefits of interior vs. exterior french drains?

Thanks so much.

We use french drains on the exterior at ground level and we tie our gutter downspouts into them. We grade our property away from the foundation as well. We have a dry basement. We did not need to dig up cement, put a french drain in at basement level, or require a sump pump. Is this the first time she's seen water in her basement? I would start by finding out the source of the water and it's point of entry. I would get more than one professional opinion and then compare all remedy options before doing as this basement contractor suggested. We live in the Pacific "NorthWet" and get lots of rain!

They want to put a french drain under the basement floor?  The only way for water to get to the french drain would be for the basement to flood.  Unless I'm misunderstanding what the plan is.

French drains are normally installed on the exterior side of a wall (the side that's retaining soil).  The purpose is to provide a sort of freeway for the water to have somewhere to go before it starts building up behind the wall and leaking into the living space on the other side.  Here's an image I found online that shows how it is typically installed relative to the basement wall:

Like @Marcia Maynard  indicated you'll want to find out for sure where the water is coming from first. If the water is coming in from the outside you don't want an interior drain system. It would be much better to have the one @Kimberly T. illustrated above. The interior drain system the "basement guy" suggested would be more appropriate if the water table in the area is high and the water is seeping up from the floor.

The basement guy makes money selling the job .  Like said before , figure out where the water is coming from . It could be solved by grading , or something else simple.

I should have been more specific. They had water in the basement about 5 times over the last 2 years. They initially thought it was from a backed up sump, because the people who installed the fence hit the sump exit pipe and filled it with cement. They removed the drywall in the basement, because of course it is finished, and there are no cracks in the foundation walls or floor. Water just seeps up from the floor. On Friday, they could barely keep up with all the water coming in, and they had 4 shop vacs.

They don't know how it is coming in. The grading isn't bad along the house. The water table is really high right now. She isn't very DIY, and is about at her limit with frustration. 

All the downspouts are routed away from the house about 12 feet. They are the only house on the street with this amount of water. All the other houses with water issues can be explained by poor grading.

Is the sump pump filling quickly ?  Is the drain tile feeding the sump  clear ?  Is the pump line clear? , Is the pump weak?   Have you checked the main water line , could there be a break ?   Are the walls wet or just the floor ?      Are the neighbors on either side having the same problem ?      These are things to check 

Best investment I've ever made on any property was a French drain. Very simple yet very effective means of redirecting the water out of the basement. You'll never regret the money invested. It's also great selling feature.

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This is the only house having this level of problems. The water is coming in so fast they can't keep up with removing it - they have 4 15-gallon shopvacs running nonstop. It seems like it is coming in from the floor. We have a drainage ditch running behind our houses that, according to two separate city employees is either not in use anymore, or still in use. So that isn't helpful at all. 

It just isn't stopping, and we did get a ton of rain, but the amount of water they have dumped doesn't seem to be connected. The quote they got was for $15,000 to install the drainage system in the basement, which would be guaranteed to not ever get water again. But I want to make sure they are doing the right thing before they drop that kind of cash.

@Matthew Paul is spot on   Wet walls requires a different approach.   If water wicks through the floor a interior French will help.  If the walls are wet I prefer a channel around the circumference of the basement into a basin for a sump pump.   The water comes down the wall falls into the channel and works it's way to the hole.   I have actually just cut grooves with a diamond  blade around the basement parameter to create the channel.  Very cheap.  

French drains can be done on either the interior perimeter or exterior perimeter. If done on the exterior, the foundation walls should be coated with waterproofing while the excavation is still open. 

I have properties done both ways, so which way to do it depends. If the water table is high as was mentioned, then doing it on the interior makes sense; the floor is demo'd and excavated until the footer is exposed, excavation should form a trench around the perimeter. Water table rises up to the trench and then enters the drain system, getting pumped out eventually at the sump pit. 

Thanks, @Steve Babiak . In the property where you had it done inside, did you ever have a leak after it was installed? The stress is really eating at them, and the first guy came out, described it as you did, and said it was guaranteed to never get water in their basement again. 

Can I ask you what you paid for it? I had a quote for my own basement several houses ago, and it was similar in size to theirs, and the quote was also similar. I don't feel they are being ripped off, but I just want to make sure they are going with the right guy.

Thanks so much!

Sounds like one of our Colorado water issues with the shut down of irrigation wells. We have a lot of issues with this in the Kersey/LaSalle areas. I will look and see if I can find a card I have for a water specialist for them.

The only thing I can think to add here is to consider getting a second or third quote.  If the answer is similar with each contractor - then that should reinforce the decision to spend the money.  I know this wasn't a technically supportive statement, but I hope it helps.

@Michael Roy , this is exactly what I told her to do. For the exact same reason. If 9 people give you 9 different answers, maybe none of them is correct. But if 9 people give you the same answer, you probably have the solution...

Installing a interior french drain isn't all that difficult, and it's even easier if you already have the sump pump installed. All it is really is renting a saw from home depot to cut through all the interior perimeter cement about 1 to 2 feet from the wall. Take a sledge hammer and break up the cement. Then dig out a trench where you broke up the cement. Line the trench with crushed stone.Then take pvc with holes in it. Face the holes down and line the trench with the pvc pipe usually 3 in pipe. Make sure to cover the pipe in some sort of material so water can come in but debris can't come into the pipe and clog up your drainage system. After all that is done tie it into your sump pump and presto. Last step pack it with dirt then lay concrete over the trench. But this sounds more like a sump pump issue, that the water is coming from there, maybe it is faulty. Because if you have no cracks I don't see water coming up from the floor. Usually water comes up though the floor through hydro-static pressure. It finds the easiest escape which are the cracks in floors, which over time if they haven't been made the water will create the cracks. This is why a french drain works because it relieves that pressure and gives a place for the water to go. Hope this helps!

The cost estimates I received for interior perimeter French drain was between $65 to $85 per linear foot of perimeter. Floor is dry through rain for the past few years, but still waiting for the deluge type of storm that caused the rising water table to occur; the 5+ inches in a few hours rain storm (n my area those are usually some form of tropical storm).   Calling it a leak is a bit of a misnomer, since the walls and floor can't hold back Mother Nature. 

You mentioned a finished basement was involved.  Does the basement have a walkout or egress windows?  If so, then those might also need to have something done to capture water to direct it into the French drain system

@Tariq B. thanks for this description. I am going to copy/paste this into an email for her. Or better yet, I will point her to this site!

@Steve Babiak , thanks for the cost estimates. No walkout. The windows don't have any water issues. 

@Mindy Jensen interior french drains are inferior to exterior drains IMO for the following reason.

Exterior and interior drains remove water to the elevation that the pipe is installed. The path of the water for the interior drains is under the exterior foundation to the drain. The path for the exterior is directly to the drain. With the exterior drain the basement walls stay dry but with the interior drain not so much. I would say that you probably won't know if there is a difference for 20 years or more. The companies selling the interior drains know this and they are significantly cheaper than the exterior style so they have an easy sell. 

This house's issues likely stem from the local geography that was covered up with the over lot grading for the subdivision. Perhaps is sits on an area that was an old local drainage and the ground is slightly more pervious allowing the local ground water to collect and move down gradiant until it hits this house's basement.

One thing that puzzles me is the why the existing sump pump is not dealing with the issue. The mere presence of the pump says there is an existing drain system. Why is that now not working?  Was it adequate before? If it was then, why is it now not working? 

Personally I would hire a local geologist or civil engineer that specializes in wet basements (this will be a small local one office firm) and pay them to come tell you what the problem is. Tell them you just want a verbal report and will pay them for their time to give you that. The cost of these people is in preparing the paper report that can drag them into court. You want a solution so ask tons of questions and take copious notes. Contractors sell products and they sell the products they install. You want some one that is paid for their knowledge. The money you save by hiring the knowledge will be saved by getting the right people to do the right solution. The geologist or engineer will likely know a few contractors that do good work at reasonable prices that they might share with you as well.

Hi Mindy. I have had an interior drain tile system installed in my house. It was roughly $5,000 for 120' with installation of new sump pump and pit.  The basement had a lot of water coming up through cracks in the floor, especially in the spring thaw or with a heavy rain. I framed up the walls soon as the cement cured and installed a new basement bathroom and pretty much finished the entire basement with no further issues. 

Going off what Tariq said, I have a couple differences. I wouldn't/didn't use PVC but rather perforated corrugated drain tile with a nylon sock to prevent debris infiltration and blockage. The cement does get broken up around the perimeter about a foot out. Dig out dirt, line with 3/4" clear gravel, place socked drain tile just under footer all sloping slightly to the sump pump pit. Then fill the rest of the way with clear gravel, not dirt along the perimeter a plastic drain membrane should be placed on top of the footer to at least an inch above the surface of the new cement floor. This allows for any water that does come through the wall to be directed to the drain tile, not on the floor. If the basement walls are cinder block then a 1/2" -3/4" hole should be drilled into each block cavity so if water infiltrates the outside of the block into the brick at any level it will flow down into the tile and not go through the wall and cause problems. We also put in a couple cleanout to have access at various points. 

The only issues that I have heard would not be with the system but rather the source of the problem. If there is a natural spring in the center of the house more then bleeder lines (trenches and tile would have to be installed into the interior of the basement as well. 

An exterior drain tile system also has benefits, in that you now have access to the exterior basement wall, which you can then seal and install the proper membrane and fill with gravel for excellent drainage but is mu h more expensive as it requires more work and many times harder to access.

The price seems a little high but it might just be your area compared to mine. I also helped on the project because I wanted to learn, so I might just have gotten a great deal.

I had a similar issue in my own home a couple years ago.  We dug around the exterior perimeter and replaced the footing drain pipe that had gotten full of dirt, sealed the exterior foundation walls, added a drain across the middle of basement to the footing drain (used a cement saw instead of sledge hammer), tied the drains to a sump pump.  Then we also added a curtain drain where the yard sloped toward the house and tied it into the pump chamber. No more problem! (Our price from a friend was about $11k). Good luck!

@Mindy Jensen

Here are some pretty good links about French Drains from just googling the subject.

Video of Installation of Interior Basement Type:  http://www.aridbasementwaterproofing.com/index.php...

Description of What They Are:http://en.wikipedia.org/wiki/French_drain

Description of Why They Are Needed: http://www.houselogic.com/home-advice/drainage/fre...

Images of Different Types & More: http://www.google.com/search?hl=en&q=french+drain+...

@Bill S. , thanks for all that information. I will absolutely share this with her. What you say about old local drainage makes me wonder.

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