Materials for French Drains
Hi all, I live in zone 4c trying to figure out how exactly to do my French drain around my house perimeter. We have a crawl space with proper ventilation and no current moisture problems to speak of. This is a built home, just re-doing a few things. We do have downspouts going into their own system (until about 15’ past the house – where the French drain line wyes into the solid line just before dicharging – by the way, this is OK, right?… As opposed to keeping the lines completely separated…
So for the design, at first I was thinking of just using the sock-wrapped perforated corrugated pipe, throwing gravel over the top of that, then backfilling with whatever was excavated… But I have since read about the importance of soil separation, that is, instead of a sock around just the pipe, you would lay down your fabric at the bottom of the trench, fill in a few inches of gravel (some say no gravel here just yet but to put pipe at bottom of trench), then lay your non-socked perforated corrugated pipe, backfill some more gravel, then wrap it all up in the landscape fabric like a burrito and slope it to daylight..
What are your thoughts on this approach? Will it work well?
and lastly, is sdr35 THAT much better than corrugated as my local supplier is telling me that it is? Seems to me corrugated will work fine and is easier to work with…
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
You already seem better off than most. I've spent some time on the French Drain Man's YouTube channel: https://www.youtube.com/channel/UCs09Xm81fnqfuilUKJvKyPw
He seems to build very well and even sells some products that might otherwise be hard to acquire for DIY purposes.
The burrito makes sense: keeps the silt out of the gravel, not just out of the pipe.
When you back fill, you want free draining soil, not clay. We made the mistake of backfilling with the heavy expansive clay that we had dug out, and we had to re-do much of it.
Kevin,
Reasons I can think of to use PVC rather than corrugated flex pipe:
- Durability. It is much harder to crush.
- Joints aren't as prone to separating.
- Doesn't get infiltrated by roots as easily.
- Can be sloped, while corrugated inconsistently follows the substrate.
- Carries water through the pipe, as opposed to alleviating pools of water as it accumulates in dips.
- Can be cleaned easily without damage.
- Our codes haven't allowed corrugated for several decades.
HD has French drain pipe it’s a type of PVC with holes.
You don’t ever want to do this job again.
Don’t line the pipe directly with filter fabric. It’s got to be a burrito.
Ryan,
I missed that. No reason to use sdr35. Ordinary perforated PVC is fine.
That’s right.
I’m talking about something like this.
https://www.lowes.com/pd/Charlotte-Pipe-4-in-x-10-ft-Sewer-Drain-Pipe-PVC-Sewer-Pipe/3362194
It’s thinner walled than normal PVC.
Deleted
+1 on PVC being more permanent than corrugated.
When you say pvc do you mean the semi flexible hdpe, triple wall(?) white on outside black on the inside, or the actual pvc smooth pipe?
The hdpe is available at Home Depot and cheaper. Pvc is available as sdr35 and a little bit more expensive and further from home to attain
The picture is the one easily available to me... the hd website calls it hdpe.
HDPE is high density polyethylene. It’s the same material (in terms of the resin) that is used for nearly everything in the utility industry — yellow “plastic” gas mains, black with blue stripes for water mains, black with red stripes for power. We in the telecom industry often use solid colors (orange, blue and green to follow the first three colors in the telecom color code). I even know one contractor who was feeling patriotic and ran three ducts, one each of red, white and blue.
The stuff you’re seeing at HD is basically an air-core (instead of solid walled) HDPE stick pipe, somewhat similar to cellular PVC. I wouldn’t worry about using it, just keep in mind that you can NOT glue to it with regular PVC cement. The pipe at HD is probably similar in crush resistance to the thinner walled schedule 35 PVC sewer pipe, but it’s less brittle so more chance it will deform instead of cracking if stressed, which is a good thing.
I’m not sure if the pipe at HD is UV stabilized or not, so unless it says it is (“sunlight resistant”), make sure to use it only underground. If you need to come up to daylight, some wraps of 20 mil black tape will provide protection from sunlight.
Bill
HDPE is good stuff. Lower environmental impact in manufacturing than PVC. And works well for this application.
It's regular 4'' pvc schedule 40 but with holes in it (at least in Canada). Don't use corrugated pipes, they will get crushed. It's just a matter of time. Ask me how I know...
Solid PVC is the way to go even though it's a bit more expensive. Something like that :
Where I am it’s commonly called sewer pvc. Here, we have to install clean outs in the line too
Kevin, in your first post are you saying the rain water ties in to your main waste pipe from the house?
I’ve dug up old corrugated flex before and it was either crushed or had roots and debris in it or both.
As far as this question: Kevin, in your first post are you saying the rain water ties in to your main waste pipe from the house? Not the waste, no. I was talking about roof water/downspouts. but this doesn’t happen until after the French drain becomes a solid pipe. the two downspouts from both ends of the house will go into solid pipe underground which will parallel the French drain and both will run separately East until about 15’ beyond/after the house and at that point will tie in with the perimeter French drain. So, essentially there are two pipes running along the house, one perf, one solid. Once they continue past the house and are both headed toward daylight, they will tie in with one another, about 15’ past the house, then run another 10 or 15’ to daylight If this is still a no-no, it wouldn’t be that hard to keep these systems separate always. Hope that explanation makes sense
I think Alex was asking if it tied with your main sewer/septic line. You don't want to tie it into septic / sewer.
If you are just saying you have multiple stormwater / groundwater systems tying together, the only limiting factor would be flow capacity, assuming you have proper pitch so that gutter water doesn't back flow into the ground system. Curious if others see any problem with that set-up.
Most storm systems combine the outflow pipe once it is away from the house.
The downside to connecting the two is that if the pipe gets blocked, the water from the downspouts will all end up accumulating around your foundation.
Another benefit to separate outflows is you can observe the discharge volume from each source, making detecting problems a lot easier. (wife shakes head, wondering why Malcolm is standing in the bushes staring at the ground again).
Alexpoi,
It's CSA certified, but thinner walled than schedule 40.
Deleted
Have you visited and watched the YouTube channel: French Drain Man?
-Are there any trees around you?
-Any chance of leaves getting into the downspouts and blocking up the system?
-What would be the consequences for you if the system became blocked and the frech drain didn't work?
-Have heard pipe in the bottom of the trench with washed stone on top of it provides the benefits of holding down the pipe and not having to wait until the water rises above the the stone before pipe starts working.
With sdr35 vs corrugated pipe: check if there is a required pitch difference as sdr35 has a smooth interior and might allow for a pitch of an 1/8" per foot vs 1/4" per foot for corrugated.
Also, is there a crush strength difference between sdr35 and corrugated? How deep and what weight will travel over the pipe?
If you get sdr35, it once came in 10ft lengths with a built in 4" bell end coupler built into the pipe.... That 4" was in addition to the 10ft length.
Seems that some professionals prefer the corrugated pipe vs pvc for the french drain due to its ability to move with the freeze cycles of the soil without cracking.
These are just some thoughts.
Finally, it's not uncommon for people to spend more to ensure the right materials were used and then just get their money back by eating mac n cheese for a while.
The hdpe triple wall is available with two hole pattern or three hole pattern... Any benefit/difference - as it pertains to French drains? The two hole is available in store, 3 hole 120° is available online but free ship to store. Maybe there’s a reason for this associated with local building codes/minimum requirement? ie 3 hole unnecessary, 2 hole suffice. Anyone have thoughts on this?