View Full Version : French drain

09-27-2006, 07:51 AM
I'm doing a french drain at the bottom of a slope. I lined the inside of trench with porous landscaping fabric then filled with 4" perforated pipe with sleeve and gravel.
I want to make a gravel path along the top of the drain.
My question is: Is it correct to put a layer of the porous fabric on top of the filled trench and add the gravel for the path onto the top of the fabric?
Or, will the water tend to run across the top of the fabric and not down into the drain? My reason for the fabric is to keep the drain as clean as possible but I don't want to defeat its primary function.

09-27-2006, 07:59 AM
I thought the perforations should actually be on the bottom. Water percolates through the gravel and into the ground underneath. Only when the ground cannot hold more water does the table in this channel rise enough to enter the pipe from below, where it is carried away to it's destination.

09-27-2006, 08:56 AM
That is correct the perforations in the pipe are placed on the bottom side of the installed pipe.
However, that is not the point of my question; which is about the advisibility of placing a layer of landscaping fabric between the top of the completed drain and under a gravel path that I want to install over the drain along the entire path of the drain.

09-27-2006, 09:08 AM
If it's only gravel on top of the trench, then IMHO it's overkill. The reason to put the barrier there is to prevent dirt from blocking the air spaces between the gravel. If yr not planting above, I think there's no reason.

09-27-2006, 10:22 AM
Here's my $0.02, might help you, might not.

Previous house had a gently sloped back yard, which intersected with a more steeply sloped hill. So a valley or "crease" or gulley of sorts was created. The clay soil (SE Michigan) didn't drain worth beans. So the crease would be very very soggy for long periods after rain.

I rented a ditch digger (mother of all chainsaws - but to dig in the earth) and dug a trench about 8" wide and the width of my yard, about 100 feet. The depth varied from about 8" at the start to 24" at the end. Basically I pitched the trench so it would meet with my neighbor's drain tile in the back of his yard. His tile was tied into the storm drain, so I "plumbed" my yard into his (with his approval), and eventually into the storm drain. The history to this is the site developer did a very poor job of grading.

I put about 2" of pea gravel at the bottom of the trench, followed by a 4" plastic perforated drain pipe, encased in landscape fabric. I bought this at a landscape supply or ag. supply place. Then more pea gravel on top of the pipe, followed by dirt then sod. Worked beautifully. Never had a soggy bottom ;) again.

I don't think performance would be affected by anything you put above it, so long as it isn't concrete, asphalt, pavers, plastic decking, etc. Grass or normal landscape items would be OK.

09-27-2006, 10:41 AM
Been reading a bit on this since yr post in the AM. The old way of building the FD's is per Chassis's post. But there's a fear (I cannot confirm) that silt will work its way into the pipe's pores. Landscape fab between any gravel and dirt is now recommended. No dirt on top? No need for fab - only on bottom

09-27-2006, 03:18 PM

The pipe I used came pre-encased in landscape fabric.

03-01-2008, 04:03 AM
be very careful of the covering on the pipe. I had a situation with a drain where it went to daylight and i could see the draining 4" pipe. the pipe was perfect for about 2 months. after that the amount of water coming out was small but perfectly clean. What happened was the sleeve was acting like a coffee filter slowing the water down. Took off the wrap, right back to perfect. So if you can see the end of the drain keep your eye on it. Also i had just 1" stone over it with no dirt just the fines from the rock is all it took to block the sleeve. about 6"inches of rock under with fabric under that. the wrap seems ike a great solution but in practise i would never use it again

03-01-2008, 04:55 PM
Also i had just 1" stone over it with no dirt just the fines from the rock is all it took to block the sleeve.

This would be why landscaping plans always specify the gravel or crushed stone as "washed" and "no fines"...

04-08-2008, 06:02 PM
I need to put a draining system in my father's back yard to redirect pooling rain water away from his house, water literally gushes through cracks in the mortar, and after reading about French Drains in this and other threads am more confused then before I started. I have seen posts that say the perforations should be up and others that say down, I thought down. Some that say use landscaping fabric or a sock, which is what I thought, and others that say don't. Additionally, I haven't found a clear consensus on how deep the trench should be, I live in Pennsylvania so does it have to go below the frost line? And lastly how much stone to use below and above the pipe.

I was going to go down about 3 feet and out from the house about 8 feet. The area where the water is pooling is flat but there is a natural slope beyond a retaining wall. So I was going to run a drop of about 1 foot down per 4 feet long.

If anyone could help clear my confusion that would be great.

Gary Swart
04-11-2008, 11:03 AM
I use French drains to get rid of rainwater from my gutters. All I did was trench, lay the pipe, holes down, and cover with drain rock then soil. It's been several years and they seem to be working well. Happily, my basement does not leak a drop, but that is not because of the French drains.

08-29-2010, 11:00 AM
My contractor is putting in my french drain but the pipe does not have holes on the bottom, only on the top and the sides.. Is it correct? Will that be effective in carrying water away or should I have him redo the pipe? thanks

08-31-2010, 03:03 PM
I am working on my first french drain, but I have literally read for hours and hours online and I understand that the holes always down (never seen a contradiction). This keeps the holes from getting clogged and also allows for the rising water table - or watever - to enter the holes quicker.


11-27-2011, 05:40 AM
I'm guessing a french drain is what I need, maybe not. The rear of our house is at the bottom of a steep slope of about 45 degrees. About 15 ft back from the house it levels out to a "platform" running the entire length of the house.
The platform is at least 15 ft wide and flat, then the land rises again. Water runs down the slope causing seepage into an unfinished basement with a dirt floor. I'm thinking trenching out at the forward edge of the "platform" would be a good place to put a french drain and have it descend to one side of the house where the sun hits the lawn. Any thoughts are appreciated.

11-27-2011, 06:20 AM
A French drain will only seep away ground water, and would never handle the volume of surface water shed down a slope. For that you need a swale as well.

11-27-2011, 09:07 AM
the only problem you could potentially have with more landscape fabric is it getting clogged up with silt, etc and then slowing down water flow. however, if this is happening, it would have worked its way down over time and clogged up the fabric around the drain line instead.

so, my perspective is this. lay fabric in the bottom of the trench, with enough left hanging out to lap back over the top when the drain is finished, creating a fabric shield all the way around the gravel. if you have problems with clogging up the fabric, its at least better to have it on the top fabric that is easiest to get to and replace, than on the fabric wrapping the drain pipe. clean fabric won't cause any significant problems, unless maybe you decide to put 20 layers down or something.

and yes, holes should always be down. there are some custom applications where you could do a holes up setup, but its not a french drain. it would be integrated into a waterproofing system where all water must be drained away. a french drain should allow water to percolate into the ground naturally, and simply carry away the excess that can't soak in quickly.