French Drain Design

French Drain Design with PVC Pipe
Our 100 year old barn was in bad shape when we bought the property. Here's a link to my barn foundation repair article. Many errors were made when the original stone foundation was replaced by this concrete foundation in the 80s, but the main problem with the foundation was poor drainage around it.

Before, looking alone side of the barn from the back. Not sure if can see it here well, but the grade (slope) is running toward the foundation ("negative slope"). (Note: click on photos to enlarge them)

Before, looking along the side of the barn from the front. Perhaps this shows the negative slope towards the foundation better. You can also see the drip line cut in the soil, from the huge amount of rain coming off the barn roof, which would then permeate the ground, right next to the foundation.

The area next to this side of the barn foundation acted like a catch basin for about 2,000 square feet of the property next to it, including a poorly designed driveway and a standalone garage placed next to and on higher ground than the barn. Add to that another 900+ square feet of rain running off the barn roof, just on this side. Every year the ground would freeze and thaw, pushing the foundation in even further. And with that, the ground around the foundation slumped even more, making the drainage problem even worse.

French Drain Design
I decided against installing gutters on the barn, as they would take away from the original, historic design. A french drain design with PVC pipe was used for the drip edge, and a swale was created to divert water away from the barn foundation.

French Drain Design Diagram

Two sticks, and a string keep my outside line straight. I dug out from the foundation about a foot past the drip edge (in hindsight a bit more might have been better). I dug down about 18". While I dug, I used a long level to check the french drain slope, which should be 1/8" per foot, or of course more downward slope is fine too.

I then laid down think plastic, as this was a drip edge, and wanted to catch the massive amount of rain water coming off the barn (Note: I've read that you don't want the soil too dry next to the foundation, as that can cause problems too, but I didn't do much beyond the swale to divert ground water, so hopefully I've struck a good balance of removing rain from the roof, and some ground water coming under the plastic to keep the soil from completely drying out).

I then added about an inch of rock to act as a solid foundation for the french drain PVC pipe. On top of that I started to put in the PVC pipe, with the holes on the bottom side.

Why the Pipe Holes Should be Down and Not Up on Drainage Pipe

Yes, they go on the bottom side. Imagine the drain filling in from the bottom up, and when it reaches the holes, the water enters the pipe and runs away. If the holes were at the top, the water level would have to get to that height before it entered the pipe. The trench would fill with a lot more water, before it was drained away.

The roll of white fabric (weed barrier) goes over the pipe to keep weeds, roots and other debris from getting into the pipe. (Note: After I filled the french drain with rock, I cut the vertical PVC pipe down to size and added a cap to it, which is my access point, should they (there's a pipe like this on both sides of the barn) ever get clogged.

At the other end french drain design, I stopped putting down the plastic and dug a simple trench for solid PVC pipe. The solid pipe goes to daylight after its well around the backside of the barn, where the water can run away.

Before I added the top layer of rock over the PVC, I check the entire french drain slope (1/8" per foot) with a level, adding rock below the PVC pipe where needed. I then cut off the excess plastic on both sides of the drain with a utility knife.

French drain materials and tools.

After the french drain was done, I went to work creating a swale further out from the barn foundation. Yes I did this with a shovel. Lots of work. You might want to consider a Bobcat rental. I didn't as I wasn't sure I could do what I wanted as I don't have Bobcat experience. You can see also that I covered my nice new french drain with clear plastic to keep dirt out of it while I worked.

Before Shown Again for Comparison to Below


Here's how the surface runoff water moves down into the swale and away from the barn foundation, or into the french drain. You can also see that I've cut down the vertical PVC pipe (on the right), leaving about 2" exposed above the rocks, in order to add a access cap that can be removed should I have to remedy a clog. You might wonder why I made the swale contour hump up right next to the drain, well, it's not ideal you are right. The reason is that I broke my back digging the 60 ft. of swale by hand, and I just couldn't bare digging any deeper in the dense clay, so I decided a few inches of surface water could run off to the drain side instead of going into the swale. Granted some will permeate into the ground and raise the water table next to the foundation, but I've read that you actually don't what the soil next to the foundation to be too dry, as it will crack and become less stable, so perhaps I've struck a happy balance between too wet and too dry. Time will tell.

The Results
This project was done in Nov. of 2005, and it's now Dec. 2008. The system has worked very well as far as I can tell. During heavy rains a small stream moves down the swale, while a heavy flow of water comes out the daylight ends of the drainage pipes on both sides of the barn. After three snowy Winters and three extremely wet Springs, the barn foundation has not shown any signs of movement, or damage.

After (not the best shot, there are some fence pieces leaning there, part of another project...)

All Worth it to Save this Barn

PVC Drainage Pipe
PVC Drainage Pipe Cap
PVC Drainage Pipe Outlet Cover
PVC Primer and Cement
Drainage Pipe Weed Barrier
Plastic Sheeting

Miter Box


Ask the Builder: Drainage Articles
Ask the Builder: French Drain
Ask the Builder: French Drain Design (slope and depth for ground water)
DDA Construction: Design for to catch downspout water and ground water
How to glue PVC pipes
How to cut PVC pipes

My Standard Disclaimer: This is what I did. This does not mean this is the best way, the right way, to building code, or even safe for your needs. So you are on your own with your project. I make no promises about the information presented here. I'm just a do-it-yourselfer, not a professional at all, sharing my story. So if something goes wrong with your project, you are on your own. Good luck, and have fun!

All content and photos, copyright 2008, Dover Projects.

My Other Articles


  1. Great Job,

    Well documented, illustrated and clearly described !!

  2. Thanks! Hope it helped you.--Peter

  3. Thank you for sharing all your hard work. My husband and I are planning to install a french drain as well. The ground in our yard is sloped toward our house. I have a question please? Should the holes in the PVC pipe face up or down? We have had several contradictory answers. I have bookmarked you page for guidance. Thanks again. Diane

  4. From what I've read they go down. That's what I did and it has been working like a charm. Hope the article helps.--Peter

  5. Peter,

    I'd like to use you before and after photos (with photo credits), and link to to this page from a free public access page on water control at residential structures I'm writing for my site.

    Here's an example of how I would use and credit your material:


    Michael Thomas

  6. Michael,

    Feel free to use my photos and diagrams any way you like. Credit and a link back would be great. Thanks very much for checking.--Peter

  7. my backache just looking at your photo of creating wales with shovel! great job

  8. Looking: Yeah, the shovel was not a good idea, but I was too cheap to hire someone and too inexperience to run a Bobcat in that tight area. I remember not being able to stand straight up, quickly, for about a week! The worse part was shoveling/moving the gravel from the driveway to the drains. BTW, I know you mean "swales" not "wales", but it did feel like I created Wales, UK. (Joke)--Peter

  9. NEW!!! DOVER PROJECTS ON FACEBOOK! Join in with your DIY spirit! Click on the BIG blue box for "Facebook, Dover Projects" in the right column above! See you there!--Peter

  10. Thanks for the clear explanation, it is very helpful: 1 question: what thickness for the plastic and what kind as when one goes to the regular hardware stores, they direct us to getting painter's plastic sheeting in 4 or 6 mil? wouldn't his kind of plastic crumble over time? thank you

  11. Anonymous, Boy... I'm trying to remember now what I got in more detail than what I say above, "thick plastic". I'm sure I got it at the Home Depot (close to me) and it wasn't a special plastic for in ground/landscaping or freezing temperatures uses or anything. That said, mine, where I can see some of the edges now, as the stones have moved around a bit, I have not seen any cracking or deterioration due to the elements. I can tell you it was think and hearty. Might have been 6. Like this

    Sorry I can't give you a better answer...

  12. thanks it still helps....sorry about the anonymous aspect just lack of time to register, we are in an old 1870s house in Oh and are "Trenching" along so the thick stone foundation can get a break..thx Sylvan

  13. Sure thing. Hey by the way, were you notified that I responded, or did you just check back?

  14. no I did not get notified (I don t think I could have as I did not enter any email anywhere, I just checked back..thx

  15. Right, gotcha. Thanks for the feedback!--Peter

  16. Peter,

    In your list of materials you didn't mention the type of stone. What type did you use for your french drain. Also, how long did it take? Thanks for the great information.


  17. Andrew, what an oversight! And I forget now what the rock/landscaper retailer called it. Ask them for the right grade and then they will have a few choices for you depending on how "decorative" you want it to be as well (and the price will go up with it looking more "decorative" too!).

  18. Peter,

    How long did the entire project take?


  19. Andrew, I think it took me a couple of weekends? Of course I contoured the grade by hand with a shovel... sore back! :)

  20. Thank you so much. I do need to have new gutters above the garage installed before next winter. But there is a huge hill behind the garage that produces run off. The water sat @the back of the garage. I hired guys and directed them to do as your instructions laid out. But I got a good deal on a pipe sock, so I used that. We weather proofed the sides of the garage and laid cardboard near it before dropping the big gravel. It looks great. I am sure it will work great. Thx again!

  21. Wow, great article. And you listed your resources. I am a first-time homeowner who never has had a knack for technical stuff, but I taught myself to work on a car to save money so I figure I can now learn to work on my house.

    Our basement leaks on two adjacent walls and I would like to finish the basement in a couple of years so I have been looking all over for resources. You saved the day with this write up as I would have done nearly as much digging just to regrade and would have missed out on the french drain system. I have three questions:

    1) So this works for someone like me who has gutters because the drainage water only seeps down into the ground a few feet until the soil is too dense for more water penetration? That's what one of your resources seems to say but I just wanted to make sure since I always thought the water just kept going down into the ground. If the water keeps descending it would seem like a drain system 2-3 feet underground wouldn't be much help to someone like me.

    2) If this is the right project for my problem the big question will be where to drain the water to. The easiest solution would be to a mysterious filled-in pit about 10-15 yards behind my house. It is allegedly the house's former well (we're on city water now). The ground fell in there several years back and the previous owner had it filled in with boulders, rocks, and soil, in that order. Now there is a depression in the ground there and I don't let my kids play on top of it. There's a chance it could also be the old sump (we're on city sewer now too). The other alternative would be a lot more digging and would require some hardscaping removal in the front yard, so is the filled-in pit far enough from the house in your opinion?

  22. I recently purchased an old house of my own and am going to be tackling many of the projects that you have already completed. Thanks for putting together projects that the average joe can understand. Weren't you on renovation realities for a kitchen do-over. Have you gotten a patent yet on your car jack countertop remover?

  23. French Drains are becoming necessary in NJ with all of the rain we have been having lately. Great article and thank you for sharing your project! It was worth saving the barn!

  24. Congratulations on a great and instructive project. I have a house in VT with a standing seam roof and no gutters. The foundation is CMU, and the walls in the basement have bowed and cracked from frost forces about 3-4' below grade on one side where the water sheds from the roof. I get some water and moisture entering the basement interior through the wall. Just the other day, a contractor friend recommended a system very similar to yours - essentially an underground gutter system that prevents the water from entering the ground along the foundation wall. He said that a foundation drain would be better, but this approach avoids the need and cost to excavate and waterproof the foundation wall down to the footings. My contractor made a few additional recommendations for my situation, which I will offer here (although the work hasn't been done yet). He has recommended: a) using a rubber membrane, such as used on an EPDM roof, in lieu of sheet plastic; b) adhering the rubber membrane up the exposed side of the foundation wall and painting it for aesthetics; c) digging a little deeper and adding 3" rigid foam insulation angled away from the house to eliminate frost against the foundation wall; and d) widening the excavation a little more. This all assumes, of course, that the source of the water is coming from surface water, as opposed to a high water table - which must be managed differently.


Please leave your questions or comments here. I love to get feedback. You can do so without an account or user names and passwords, etc. Just select "Anonymous" next to "comment as". Thanks!--Peter