French Drain Question

[dave1949]

I need to eat a little crow here. When I goggle "French drains" several pop up that are as the OP described.
I call those side drains or just under drains though most shown on Wiki have more elaborate top dressing then anything I've installed. They all appear to be quite functional as long as the bottom of the ditch is graded properly. I would think that loam and grass sod over the top of one would work but at a slower rate as long as the loam was more sand then clay.

I never really paid much attention to the definition. These types of drains have certainly changed over time with new materials and such.

At our old house, that had no gutters and I didn't want the headaches of the things anyways, I built a surface drain below the eaves by scooping out a shallow trough, laid heavy plastic in it, formed the outer edge with landscape timbers, and filled it with 1" to 1-1/2" washed stone. It was 40' long and about 2-1/2' wide with a good slope, at least as much as a normal drain line has.

So, I tested it to see how the water would run by laying the hose on the high end and letting it run. What happened was the stone saturated with water, but the water did not travel through the stone very quickly. It was spilling over the edges as much as running out the low end of the trough.

Okay, Plan B. I dug out enough stone to lay in a rigid 4" plastic drain pipe with holes and covered it with stone. That worked very well.

That is how I learned the relationship between the stones and the drain pipe. Stones alone do not transport water very well at all, which is why you rightly think poorly of that style of french drain.

 

[s219]

I covered my french drains (which had a 4" corrugated pipe embedded in #57 gravel and wrapped in septic paper) with about 4" of top soil (sifted, with no clay) and then planted grass over the top. Has worked great for many years.

 

[BoFuller]

I am also going to install French drains soon. My foundation stemwall is done except for the drain and water sealant. I'm planning on going with the 4 inch hard PVC pipe (with holes) instead of the flexible pipe. My drain will be down 4 feet at the high side and 6 feet on the low side. My inspector says I should sleeve it but I've heard of sleeves clogging up. Would a roll of mesh be better? With a few inches of gravel on top of the pipe before folding over the mesh? I should put a tee and a clean out on the high side too?
How about sealing the block? Any good roll-on sealers I can use. It's just a crawl space, but I want it as dry as possible.
I'll have big overhangs, and eventually wrap around porches.

 

[dave1949]

I am also going to install French drains soon. My foundation stemwall is done except for the drain and water sealant. I'm planning on going with the 4 inch hard PVC pipe (with holes) instead of the flexible pipe. My drain will be down 4 feet at the high side and 6 feet on the low side. My inspector says I should sleeve it but I've heard of sleeves clogging up. Would a roll of mesh be better? With a few inches of gravel on top of the pipe before folding over the mesh? I should put a tee and a clean out on the high side too?
How about sealing the block? Any good roll-on sealers I can use. It's just a crawl space, but I want it as dry as possible.
I'll have big overhangs, and eventually wrap around porches.

I don't know about the sleeve/no sleeve thing. Muddy water (suspended particulates) surely passes through the mesh/fabric, into the stone bed, and on into the pipe. It may depend on the nature of your soil as to whether that would clog a sleeve eventually.

Logically, if the fabric protecting the stone bed fails to do its job, the drain will not be very effective due to clogging material in the stone. Looked at from that perspective, the sleeve on the pipe will not save the drain from eventual failure. If the fabric is working, then the sleeve represents an unnecessary point of failure if that is the nature of the soil.

Don't skimp on the washed gravel.