I'm installing a sump pump and a bit of drain, in a clay soil basement that happens to have a spring. It is silty fine clay that has a habit of migrating with water and clogging everything.

What are the best drain rock types for this situation? Road base? Pea gravel? River rock? Crushed rocks? Can you supply references to tests or building science on this answer?

In this case it is possible to flush the area every few years with clean water, as it is possible for the gravel to reach the basement grade level. The hope is to dry out the soil in summer to reduce rust on the pipe and tree root growth.

Here's the temporary utility pump, used to lower the water level:

enter image description here

  • That yellow stuff is low viscosity foundation crack foam from radonseal.com , which did work. But now the water just pools rather than entering the adjacent room. – Bryce Mar 29 '18 at 5:54
  • What purpose will the rock serve? – isherwood Mar 29 '18 at 21:10

That's a pain, but I think the standard advice for outdoor french drains applies. 3/4-inch minus rock and def filter or landscape fabric (not the plastic kind, the woven kind). But from a quick bit of browsing, you might want to layer filter fabric down first then rock then a socked pipe (keep the sediment from even getting to the rock, like an outside french drain.

You are going to get some sediment in your sump bin. Just make it large enough to justify the work and perhaps be able to get a secondary backup sump in there comfortably (either a battery back up or water).

Not quite the building code information you were seeking, but it does sound a lot like you would benefit from thinking this is an outside drain in clay soil.


  • Don’t you mean 2” to 3/4” or 3” to 3/4” round river rock? You don’t want 3/4” minus rock, because it has “fines”. You don’t want “fines” in you French drain... – Lee Sam Apr 7 '18 at 5:27
  • Thanks for that. Yes. I've seen working systems with those, but not that soil. I will say that I would go with smooth perforated PVC (I see something black in the pic), I don't envy him that basement, but I do envy him the project. Makes me want to get a jack and increase the size of my sump pit. Not going to happen, but... – IGotAHeadache Apr 7 '18 at 11:32
  • I favor pea gravel because it doesent pack like crushed quarry but agree with fabric and perf pipe. – Ed Beal Dec 13 '18 at 19:18

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