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I live in Southern California, it barely rains here. However, I am working on my yard and just built a retaining wall and was required to use perforated 4" pvc pipe behind it.. Now I need to do the other part of my yard and Im wondering what's the best solution for the drainage. Can I just just use the solid pvc? HOA is requiring me to install drainage, but no requirements as to what material to use. Anybody has an advice to what's the best solution would be? 4" solid pipe? it will drain to the front yard where we are required to have pea gravel for that reason. And if solid PVC is the right material, do we need the gravel on the trench at all? Thank you.

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  • The only good a solid pipe will do for drainage is if you run a hose into the top end to drain to the bottom. Quite a few places where it barely rains are getting flooded out now.
    – crip659
    Jul 16, 2022 at 22:29
  • What do you want the pipe to actually do? Do you want it to carry water coming in one end and out to the other end, or do you want it to collect water all along its length and carry that water out the end?
    – brhans
    Jul 17, 2022 at 0:50
  • While your experience may be that there's little rainfall, codes are usually there to handle both normal weather and exceptional events. A brief search, indicates that seasonal rainfall in Los Angeles varies substantially, and that there has even been at least one federally declared disaster involving storms in multiple Southern California counties, and a state declared disaster for storms in Southern California as recently as 2021.
    – Makyen
    Jul 17, 2022 at 17:12

2 Answers 2

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A solid pipe will do no good as a French drain. If draining water away from a foundation I use a perf pipe in a “sock” the sock prevents dirt migration but allows the water to drain.

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  • I generally avoid the sock method but do a bottom piece of landscape fabric, the perf pvc, 3/4 crush then a top piece of landscape that wraps to the bottom. This enlarges the surface area in the landscape fabric and is less likely to clog with fines. Code where I am forbids the sock due to clogging. Jul 17, 2022 at 2:41
  • I use the sock over the pipe rock then fabric and have never heard of it being against code as the sock I use is the same as the fabric sounds like someone doesn't understand the use of the sock to prevent the gravel and fines migration,
    – Ed Beal
    Jul 17, 2022 at 2:51
  • The pipe helps to drain the water away , the pea gravel creates a large area to collect the water and allow water movement, where crushed rock and shale will compact and be a less effective drain field. Making a drain that will last usually you dig your trench put the landscape cloth in perf pipe of what ever type with a sock for longer longevity fill with gravel over the pipe to ~6-8” below surface and fold fabric over then fill the trench up with soil sod or fill completely with pea gravel if required by the HOA. This is a classic French drain and will catch redirect the water from the wall
    – Ed Beal
    Jul 17, 2022 at 17:57
  • I've watched some home improvement shows where the sock ended up clogging preventing the drainage from working. I suppose in my area they must have codified against the sock. They were fine with effectively a larger sock that just wraps the 8" x 3' drainrock area. Preventing fine from mixing with the drain rock is the main idea. 3/4 crushed won't compact given it is uniform in size. pea gravel should work fine as well. Jul 17, 2022 at 22:28
  • Fines for clog them up I have been doing them like this for many decades as a sock is required around building foundations in my jurisdiction
    – Ed Beal
    Jul 18, 2022 at 2:14
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I'll show you the two things that are recommended where I live in upstate New York (but we get occasional torrential rains here):

It's called perforated pipe. First, here is the kind, black, that can be bent into a gentle curve:

black perforated pipe

Hopefully you can see the slits that allow water to go through. It comes in 6 inch or 8 inch diameter. For residential projects, people generally use the 6 inch. You can buy it at Lowes or Home Depot, in 50 or 100 foot rolls, or in ten-foot lengths which you can join with connectors.

Here is the other type, white, rigid, with small round holes. If you need to turn a corner with this system, you need special connectors.

white perforated pipe

This kind is a bit more expensive, but it's very good for areas where you're having trouble achieving a 3% drop (in absolute height), because in such areas it's hard to shape the bottom of the trench extremely precisely.

I like to use two-inch river rock (no sharp edges) instead of pea gravel, as the larger the rock, the greater the total pore space. Clayey soil and pea gravel, over the years, can cement themselves together quite effectively. Here's what the river rock looks like (the label will say 1 to 2 1/2 inch diameter):

river rock

Aesthetically, I like the appearance and texture much better than pea gravel.

You can have a truckload delivered or you can buy a bunch of reasonably-sized bags at a big box DIY store. If you have a truck, bulk makes sense because you won't have to pay the delivery fee.

You can buy a sock material, but I think landscape cloth gives better protection.

The project will have less encroachment of weeds if you dig all the weeds out completely before you begin, and if you weed the finished project regularly. But there will probably be sections, away from the house, where you'll want to lay the removed sod back on top when everything else is complete. I do use landscape cloth, but test it first to make sure that water can drain through it.

There are different schools of thought about where to put the landscape cloth, and I'll let you read about them on your own. For example you can simulate a sock by wrapping a long rectangle around the pipe lengthwise.

As you are leading the water away from the building, you'll want the pipes to point somewhat downward, at least slightly. The ideal is at least a 3% grade, but less is possible in a pinch.

Note that in some sites you don't really need all this gadgetry. You can just shape the landscape to make gentle downward-pointing swales that take the water where you want it to go, as surface runoff water.

The raison d'être of all this work is to lead water away from the foundations of the house, or in your case, from the retaining wall. The easiest way to deal with the water is to deliver it to the street with a pipe that goes under the sidewalk.

The idea behind perforated pipe is that it will allow some water to filter out through the openings and drain into the ground, and it will also carry water from Point A to Point B. So, a combination approach. Another reason to perforate the pipes is to enable them to capture water along the pipe's length.

It sounds like your ordinance may have been written many years ago when the microclimate in your area was less dry than it is now. Or it was lifted whole, with no editing, from a different region.

I hope you can enjoy the silver lining of the aridity where you live, that protects you from torrential rains.

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  • I am curious you mention testing the land scape fabric and against a sock , the socks I use are made of landscape fabric has tiny holes or is water permeable, if water can not move through it would be plastic sheeting. 2+” is not pea gravel as the op specified.
    – Ed Beal
    Jul 17, 2022 at 17:41
  • Hey @EdBeal - I'm having trouble taking your meaning because of your stream of consciousness style of writing. / I have seen an expensive form of landscape fabric whose pores are so small, the flow of water through it is inhibited. I was just advising staying away from that kind. / What are you saying about pea gravel? What I'm saying is that it is often used for drainage projects but I don't like it (and I explained why). / I'm happy to compare notes with you but can you please help me understand your views with clearer writing? Jul 17, 2022 at 17:57
  • Look in the question the op specified pea gravel was required, if washed the sock may not be needed but the cost of a sock is much less than washed pea gravel if washed is available in your area.
    – Ed Beal
    Jul 17, 2022 at 18:03
  • @EdBeal Can you divide it up into separate sentences? The period would be a helpful marker to show where one sentence stops and the next one begins. I realize pea gravel is often recommended. In OP's region I guess it doesn't really matter, but in my area, river stone will make for better results, over a longer period, than pea gravel, in my opinion. / Choice of porous material is separate from sock vs. landscape cloth. Jul 17, 2022 at 18:34

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