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Which one is preferable if you have a straight line 2 feet deep trench in mostly clay soil?

I'll put either one in a sock with gravel.

There are some roots around the trench so I thought the solid pipe would be sturdier.

Any comments on this would be appreciated.

Edit: I need more comments please.

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4 Answers

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Tim Carter at AskTheBuilder.com has a lot of articles on French/Trench drains. He likes solid pipe and I agree. You are correct in that the holes point DOWN. Here's why - the water won't magicially find the holes if they are pointed up, but if they are down, the water can fill the trench and then flow into the pipe. Put a cleanout on the upper end if you can, if you don't want it sticking out of the ground, then come up with a 45 elbow and bury the cap right below the ground. I would NOT put a sock on the pipe. That will just clog. If dirt gets into the pipe, most will flow out because its rigid, and hopefully you can put a cleanout on it, or you can run a snake in from the outlet. I would put some straw or landscape fabric right under the top soil. Use 3/4 gravel as filler, not smaller. Read Tim's articles if you get a chance.

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I was going to put not only a sock but also garden fabric around the gravel (all 4 sides: bottom, sides and overlap it on the top). My thinking was that this way the sock has lower chance of clogging. – Peter Q Apr 21 '11 at 11:46
I had not thought about the clean out on top; thanks for the idea. – Peter Q Apr 21 '11 at 11:51
Use the garden fabric to line the ditch, that should be sufficient. We had to redig a ditch that hadn't been lined, basically to wash the silt out of the gravel. We put back rigid pipe with ground cloth lining the ditch between the gravel and the soil. This was the first French drain we'd installed on the property. The two others all were ground cloth lined and seem to be holding up quite well. The first ditch took about 15 years to clog up, the second has been there about 18 and is flowing as well as when it was first put in. – Fiasco Labs Jan 28 at 22:19
up vote 4 down vote

Use the solid pipe -- two feet of clay soil will be very heavy, especially when wet, and I can see the flexible pipe deforming as you fill in the trench, potentially causing a blockage in your nice new French drain.

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I'll have gravel around it; all the way to the top possibly. – Peter Q Apr 21 '11 at 2:05
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@PeterQ: that's not going to be as bad, but in the meantime I found this link that gives more reasons not to use corrugated: rigid is easier to install and easier to clean out afterwards if you need to. – Niall C. Apr 21 '11 at 2:10
The solid pipe has round holes that are of large size. The flexible corrugated pipe has slits that can easily get clogged. – Fiasco Labs Jan 28 at 22:06
up vote 1 down vote

Sorry, I have to disagree to solid pipe. Regardless of what type of soils surround the trench, the back fill for the drain must be pea stone or gravel. If you use solid pipe, how is the water going to enter the pipe to be drained? Solid pipe would be fine for a floor drain etc, but by definition, a French drain is a continuous porous downhill drain. Use the flex pipe, point the holes up and cover it with landscape cloth, and backfill with a good draining material.

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But, shrilock, the solid pipe does have holes: 2 holes on either side of the bottom line. That way the water is allowed to get into the pipe while still allowing the water to flow at the bottom of the pipe. – Peter Q Apr 21 '11 at 2:04
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@PeterQ: confusion over terms -- solid vs. rigid. :) – Niall C. Apr 21 '11 at 2:08
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yep Niall, I made the assumption solid pipe was like conduit pipe. Any perforated pipe will work, rigid or flex. The corrugation on flexible pipe actually make it quite strong however. – shirlock homes Apr 21 '11 at 6:13
Apologies for the confusion over my misuse of terms. @shrilock, what about cleaning the pipe? – Peter Q Apr 21 '11 at 11:42
Once you have buried your drain pipe, you can't really clean it unless you have intentionally made a clean out port with a street Y or something like that. If you wrap the pipe in a good silt filtering landscape cloth or pipe sock then be sure it is covered with stone before backfilling with gravel and final topsoil, you shouldn't have any cleaning requirements for many many years. you can also add a layer or cloth over the stone for double protection from silt infiltration. – shirlock homes Apr 21 '11 at 12:10
up vote 0 down vote

if you use rigid pipe with holes on the bottom, what's to keep the water IN the pipe. if water can seep into the pipe can't it seep out as well? rigid septic drainfield pipe have holes but they are to let septic effluent seep out into the ground. my preference to create a french drain has always been to dig a trench, line the trench with landscape cloth leaving a generous amount at the top to use later. then install the perforated, corrugated pipe, and cover with gravel to whatever depth will accomodate the amount of water runoff you are trying to achieve. at that point i would wrap the gravel at the top like a burrito and finish off with some sort of landscaping such as bark mulch or a layer of sod. sod will need 3-4 in. of soil to grow in. if you have a groundwater seepage problem be sure and make the bottom of the trench lower than the flow of the groundwater. if i were to use rigid/ perforated pipe for a french drain, i would position the holes on the sides, leaving the bottom solid so the water could flow out to daylight thru the street curb or whatever.

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It's a French drain. The gravel filled ditch captures the water, the perforated rigid pipe is a drain at the bottom of the ditch that offers free flow. You need holes in it so water enters the pipe and flows out. Quite the reverse from what you ask in the first sentence. Anyone who has had to install a French drain understands that no water is going to be seeping out of the pipe, you have so much water flooding the ditch that it will be rushing into the pipe to flow to the outlet. – Fiasco Labs Jan 28 at 22:11

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