Hey everyone! I'm gearing up to install a section of a French drain around my house this summer and I need some clarity on a couple of things. I'm using permeable fabric (a non-woven geotextile) that will wrap around a perforated pipe along with drain rock. Specifically, I'm wondering if I should put any gravel underneath the fabric at the bottom of the trench. I've come across mixed opinions: one side says crushed rock can help prevent soil from clogging the fabric underneath, while the other side argues that it might hinder water from reaching the downward-facing holes in the PVC pipe. Any insights would be appreciated! Thanks!
2 Answers
I don't think you need to add stone under the fabric. If you're worried about soil clogging, remember that the fines in the soil will just get stuck in the gravel anyway, making it a solid mass in no time. Stick with what's tried and tested: use rigid pipe instead of corrugated, and make sure you're wrapping everything correctly with non-woven needlepunched geo fabric. A minimum of a 4" stone bed below and above the pipe should work great. That's why it's common to install at least 16" below grade—4" of stone, then your pipe, another 4" of stone, and finally 4" of soil on top.
I believe having rock both below and above the pipe is the way to go based on my own research. The rock helps with water flow; the water enters and drains effectively. By the way, I'm curious—should the holes in the pipe be facing up, down, or all around?
The holes should actually point down. They're not positioned exactly at the bottom but more like between 4:30 and 7:30 on the pipe. That way, the water can flow into the pipe efficiently—thanks for bringing that up!