French drain questions...

[John_M]

How deep does a french drain really have to go?

I have read several sources that indicate that they go only about 2 feet below ground and others that say at or below the footer.

I would think that if you get too deep, compaction would not allow much water to get down there.

My building site is on a slope and the inspector is recommending that I install french drains.  When on a slope, is it allright to bring the ends of the pipes out to daylight...have them run out on some gravel, almost like a stream bed?

[Amanda_931]

Seems like I've heard outside of the footings, my barn has it under a rubble trench foundation (with a second quite shallow drain buried in gravel outside of that) and somebody in Serbia on another list was going fairly shallow.

In any case, drain to daylight.  if you've tons of mosquitoes, might do either a screen tied around the end or run through coarse gravel?  I don't know but with that corrugated pipe they use around here probably ought to do something.

[Billy Bob]

Here is a link to a DIY article on French drains, which matches my understanding of what  they are, i.e. a way to handle surface runoff along the roof drip line, versus a deeper foundation drain.      

http://www.gardenadvice.co.uk/howto/garden-build/frenchdrain/

[glenn kangiser]

The higher you put your French drain, the less effective it is in stopping anything that gets past it -actually it can only take away most of what is above it - the rest will continue down until it disperses in either the ground or your basement.  Ideally if you want to keep your floor dry for sure the bottom of the drain is going to be below your basement floor level and drain to daylight (sloping down) to get that water away from the floor - shortest route out from both sides is probably best.  After that, what continues down won't bother you.

[John_M]

Great information everyone...thank you!  

[PEG688]

 Only thing I'd add is below the floor , and if ya can't go down hill to day light a sump pump, in a big pipe ,with a cover for assess to the pump,  that  the drain can drain into , then the pump takes over pushing the water collected to daylight.

We did a job a few years ago like that . We hit a spring or at least a run off point that wouldn't quit .   We dug a ditch 3 or 4' wide filled it , the ditch with 1 5/8 " misus drain rock , like Amanda mentioned, put drain pipe in the ditch , drained the pipes into a 18" round pipe , set veritally, put the sump pump in that .  Rigged up a float switch , and[highlight] proper elec . hookup[/highlight]. Working great  

 Good luck , I hope all you need is the pipe and rock The cost was not figured into the bid for the extra work , Although I think the folks and the boss shared the added unseen cost of the situation.

 PEG