French Drain Depth

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24 Oct 2021
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Hi Guys,

I'm in the process of sorting some french drains myself. I'm doing them the recommended way, trench lined with a geotextile fabric, perforated drain at the bottom and then filled with stones and wrapped into a burrito. On top of that we will be putting decorative stones.

The width of the trench is 30cm, and we had planned to go 30cm deep. I've begun digging and have found that it becomes significantly harder around 27cm. More so towards the back, thicker clay and rubble pretty shallow (typical new build). Had to pull a paving slab out that was mostly in my garden but buried next door too, luckily only slightly so I didn't cause their garden to collapse!)

I've been reading about it, and there's mixed views on it as always! The main concern when it comes to depth is if turf goes back over and someone was to try and stick a fork in it. Nobody is going to stick a fork in it as it's got stones on top and even if it had turf, it'd hit the stones around the drain first anyway. Also encountered one object at one point that is 10cm deep that I'm pretty sure I won't be able to get out, it looks like an old branch that is significantly running across garden borders into nextdoor. Looks very much like a pipe but I am thinking surely not at 10cm depth.

The drain itself is 110mm wide, so I can use the first 20cm for the drain then 7cm is more than sufficient for the decorative stones, if not a little overkill.

Am I missing anything? My main concern is the depth as there's definitely some mixed views on it but it's hard to find what's relevant. I've seen people talking about frost driving the pipes up, but then I realise they're based in North USA / Canada so that's a bit more than the frost we get here!
 
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Look up the weather for 1963 and 1947 then. Global warming makes it less likely, but not impossible. My Father has a pic somewhere in the attic where he is on a Nottinghamshire country lane standing on the snow and gently resting his hand at waist height on the top of a telegraph pole.
 
Look up the weather for 1963 and 1947 then. Global warming makes it less likely, but not impossible. My Father has a pic somewhere in the attic where he is on a Nottinghamshire country lane standing on the snow and gently resting his hand at waist height on the top of a telegraph pole.

It's not something that happens in North USA /
Canada after one year so unless we get successive record breaking years I'm not concerned about that aspect.
 
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shallower than the depth of what the drain is draining into. fall needs to be at 20mm per meter of run.
 

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