Foundation drainage questions & answers:
Questions & answers about how to install, troubleshoot or repair footing drains or foundation drains around buildings.
This article series discusses foundation drain specifications & types of drainage systems, including foundation drains or "french drains" for preventing wet basements and crawl spaces.
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On 2017-02-12 15:00:16.048657 by (mod) - risk of undermining footings if foundation drainage is improperly designed or placed
Footing undermining from drainage can be tricky: the movement of water through the soils carries away fine particles along with the drainage of water itself.
The risk of undermining and footing movement depends on a number of variables such as soil type, water movement volume and velocity, distance as you noted, and other precautions that were or were not taken. An engineer expert in soils and foundations would doubtless add more.
Construction using a geotextile around the trench, gravel fill, perhaps come compacting, may reduce the risk. Certainly there are probably millions of interior trench and drain systems that have been installed as well as footing drain systems that have not undermined the foundation.
The worst undermining I've seen was done by excavation itself. A dope like me with a shovel.
Also see the illustrations in this article, such as https://InspectAPedia.com/Energy/Wet_Basement_Prevention_1c.jpg - click to enlarge any of our images.
John Eakes article that you cite is helpful but incomplete and does not address the undemrining issue. However he does make this important remark - quoting
Richard Kadulski strongly promoted this and drainage layers under the footing in Solplan Review in November 2003. The only caution that is necessary with digging below the footing is to remember that the structural load on the soil under the footing extends out at 45 degrees on either side. Hence, you should not dig right alongside the footing but a bit out from it to maintain the bearing capacity of the soil.
On 2017-02-12 01:51:18.060526 by Anonymous - more on where to locate an interior or exterior footing drain
I was concerned about it. I found some info. on the matter. I was thinking about going about 2" below the footing. Here is a link to what I found: http://www.homebuildercanada.com/1902footings.htm.
It looks like if I stay a little bit of distance away from the footing, things should be okay.
On 2017-02-11 18:15:29.380528 by (mod)Tyrone
On 2017-02-11 05:06:01.223584 by Tyrone - where to locate an interior or exterior footing drain
I am going to install interior drain tile along the footing. I have seen diagrams that show from bottom to the top: gavel, pipe, gravel, drain board, concrete. These diagrams usually show the lowest point of the gravel at the lowest point of the footing.
My footing is only 6" thick. Given that I would like to use a 4" PVC pipe with holes in the bottom, that would allow for approximately one 1" of gravel below the pipe and 1" above the pipe. Is there anything wrong with putting gravel below (not under) the footing?
Is there some landscaping fabric I should use to reduce the likelihood of the pipe getting clogged? Is it necessary to slope the pipe? I was under the impression that the objective is to create a void and once water gets up to a certain level, it will go into the sump basin.
On 2016-10-03 17:58:46.869116 by Mike
Do you have examples describing how an exterior perimeter drain tile should be laid along an above grade walk-out basement wall?
My basement slab along the N wall is 8ft below grade but the slab along the S wall facing the backyard for the most part is at grade. to be precise the slab at the SE corner where the walk-out basement door is placed is at grade.
The basement slab in the SW corner is about 3ft below grade. I can see the exterior perimeter drain tile corrugated pipe exit to daylight at the SE corner but I do not see a similar corrugated pipe exit to daylight in the SW corner. I am wondering if there even exists a section of drain tile along the S wall?
On 2016-09-29 23:58:06.142613 by (mod)Anon:
On 2016-09-29 18:56:56.876944 by AnonymousCorrect me if I'm wrong, but if gutters overflow the water will hit the poly sheet that starts at the bond/band tight against the house at grade. The water will then run at a 45° down to the drain pipe 8' away from the house. The only water that will get around this is rain that gets around the window well covers or flows under the drain 8' back over to the foundation.
On 2016-09-28 19:08:46.877894 by (mod)Wayne:
On 2016-09-26 13:54:59.168190 by Wayne
Thanks for all the help. This past weekend I rented a mini excavator and dug a trench about 8’ from the foundation along the entire wall that has the drainage issues. I sloped the trench and ran it out to a 50 gal dry well about 20’ from the house in an area with lower grade.
The trench started about 36” deep and was ~ 42” deep at the entrance to the dry well.
I used perf drain pipe wrapped in fabric and a lot of round stone. I laid 8-mil landscaping poly sheeting starting at the band of the house down to this French drain at a 45° angle to help direct water away from the house. I’m finishing up the backfilling today but I’m happy with the results for a DIY solution. Hopefully combined with some better waterproofing of the window wells/covers this will solve my basement rainwater issues on the outside of the house.
Interestingly I found a 4”clay drainage line about 6’ from the foundation about 30” deep running parallel to my trench. I have no idea what this drainage line was used for or where it ran originally as it heads towards an area of the house on a slab and on the opposite side of the house as the septic.
The drain line was heavily damaged from the original window-well replacement so I just left it alone. There is nothing inside the house I’m aware of that could connect to this. I suspect it might have been an original downspout drainage line 50+ years ago.
On 2016-09-16 14:58:40.032909 by (mod)Yes, in many businesses company managers/owners see pretty quickly where the easier, more profitable work is to be found, and many consumers also are sorely tempted by the magic bullet solution.
On 2016-09-15 11:52:29.205749 by Wayne
Thank you for the idea of the exterior sump. I did not know that it was an option and I'm glad to have other options. I have sloped covers on the window wells and they are flashed to the side of the house... but if rain is hard enough to hit the side of the house it will still flow straight down into them.
The trick is going to be finding a contractor in the S.E. Michigan area who might be willing to work with me on the outside of the home... every company I find through online searching either isn't interested in such a small job or specializes in interior systems.
I did find one guy yesterday who proposed an interior system that seemed better than the others at a much more reasonable cost but I'm going to keep trying to go outside first. Thanks!
On 2016-09-14 17:42:02.260509 by (mod)Wayne,
On 2016-09-14 17:09:20.630165 by Wayne
We renovated a house built in 1949 with no footing drains, no sump pump, etc. We knew there were basement rain water issues when we bought the property but grading was so poor we hoped that we could fix the problems with proper grading, downspout extensions window well covers, etc.
All water is entering the basement at the floor to cinder block wall joint along a single 25’ wall where there are 3 window wells. All other basement walls are bone dry. I have yet to find a contractor who can propose an exterior solution… they all only want to install an interior system. G
ravity drainage from this exterior wall to daylight is not practical due to the lot layout. Soil conditions on the property range wildly from pockets of sand to clay (I had perk testing done at a few locations for a future new septic system). I also had a sub-slab radon system installed since our radon levels were off the chart high and I continually monitor with a digital meter. Since our attempts with exterior fixes we have only had minor puddling inside the home during the heaviest long torrential rains which accumulated several inches over a period of days.
What are our options for exterior drainage or should we seriously consider interior? If we excavate the entire 25’ wall to the footings to add foundation drainage will we need to bore into the interior for a sump pump since gravity drain to daylight is not practical? Is adding an exterior cistern or dry well away from the foundation at footing depth an option with or without a sump pump? Other ideas?
On 2016-08-17 14:33:28.882316 by (mod)
A gravity drain to daylight always a superb solution to both draining a wet area and also lowering water under and around a foundation to stop water entry IF you can get one working.
There are of course some questions that remain:
- does the drain-to area flood so high that the gravity drain won't drain in your area?
- does the drain-to area flood high enough to back-flood into the home? (check valves can work there)
- what is the actual drain destination and is it one that is permitted by local codes? Some codes don't permit surface runoff or groundwater drainage into a sewer system (as opposed to a storm drain system) because it overloads the public sewer and caused raw sewage discharge somewhere.
On 2016-08-17 14:26:00.222592 by Bill moldetas
Have a question-I've had several floods in the past ten years and have installed two pumps and a generator-most recently we had a power outage and my generator didn't kick on because of a dead battery. Fortunately main power went on in two hours with no flooding. I contacted a local contractor who has. been around for forty years and says I have a high water table and that is why pumps are constantly running during a storm.
His solution would be a gravity drain to daylight placed under footings two feet into the gravel of footing floor plan. He says the water would flow right out into the street or sewer. He claims he has done a lot of these gravity drains. Is this a feasible solution.
On 2016-06-06 22:05:11.368234 by (mod)
Well sort-of: if you hire someone who waves their arms about but doesn't know about pipe location methods you could waste your time and money.
A plumber can use a plumbing snake and matching drain locating equipment to find the route of the footing drains; but it's not easy unless some fool connected downspouts to footing drain (a mistake that overloads the footers and invites basement water entry).
Without any indoor (sump pump?) or outdoor (foolish downspout) connection into the footing drain you'd have to excavate to find it at the house.
Before doing that I'd walk the site, starting at the corner of the building that's met by the lowest level of backfill or that's closest to the downhill portion of your building lot. Look for a depression, signs of prior water erosion, or similar signs.
Depending on the elevations and depth of backfill around the foundation your contractor will next decide where to make a test excavation, perhaps cutting a trench across where she thinks the drain line is likely to run.
If you find the drain line anywhere along its route you can guess at its direction, make more test excavations, or hire a plumber with pipe locating equipment to finish the job.
On 2016-06-06 18:26:01.026963 by JenniferIs there any trick to help in locating a buried footing drain outlet?
On 2016-06-03 17:12:56.935670 by (mod)Yes, Teresa from any of several causes such as
On 2016-06-02 21:54:37.540036 by TeresaIf a house was built with footing drains in 1998. Could they be clogged? No sign of muddy water in sump pump and sump pump hardly runs. 3 piece constructed basement. Noticing moisture around floor-wall joint
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