# French Drain or Trench Drain



## concretemasonry (Oct 10, 2006)

If you want to intercept the water from the slab, you should use a trench drain. A french drain is for collecting water from below the surface. Once you collect it in a trench drain you will have to drain it by gravity (probably in a solid 4" pvc pipe) to an appropriate area. The cheaper, flexible pipe has grooves and possible bellie that can collect and plug the pipe if there is debris (sand silt, etc.) from the car droppings and driveway.

A costly alternative is to tear out a section of the concrete and replace it with concrete that drains to the side and then deal with it later.

Dick


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## crankcase (Sep 21, 2010)

If your going thru the trouble of sawing the concrete to install a drain do yourself a favor and form your own. The 4' plastic one you buy at the home stores are a pain to clean out because they are rounded at the bottom. Rent a concrete saw and carefully measure and saw out the concrete. Keep the whole trench at least 12" wide and you will have to form up a 1" ledge for bar grating to sit on top on each side. Then figure for a slope in the bottom toward a 3" or 4" PVC drain. keep the bottom flat so you can clean out and sand or debris with a flat shovel. You will need to saw a narrow path to get your drain line in and knock a hole in your block to get it outside. Then you can bury a sump basket outside with a bunch of holes in the bottom. Mine is tied in to my gutter downspouts in perforated drain tile in the yard. 


The first pic shows the grate at the shallow end of my drain removed. Here it is about 4" deep. My drain is 14' long and about 10" deep where the outlet is. For that I have a 3" PVC come up from the bottom of the trench floor, but don't cut it off flush with the concrete bottom. Leave it stand up maybe an inch or so. That way the silt won't go down the drain. 
We live on a gravel road and my garage has in-floor heat and hot/cold water, so I am washing cars even in the winter. I just squeegy all the water, sand, salt and even sweep the floor right into the drain (just don't intentally sweep it in over the outlet). Maybe 2x a year I use the wheelbarrow, flat 8" shovel and clean it out. 

The second pic was showing the detail of the ledge that the bar grating sets on.


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## mikeylikesit580 (Sep 28, 2010)

Thank, My driveway is actually gravel sloping down to the driveway, so it might be easier than I think to dig a trench.


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## crankcase (Sep 21, 2010)

Oh my mistake your on the outside of the garage. So you could do the same thing in an apron just before the garage door. Heck you could even lay in a piece of perforated drain tile with a sock on it.


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## mikeylikesit580 (Sep 28, 2010)

crankcase said:


> Oh my mistake your on the outside of the garage. So you could do the same thing in an apron just before the garage door. Heck you could even lay in a piece of perforated drain tile with a sock on it.


So basically I just need to dig a trench that has a bit of an incline on it to make the water go somewere. What should I line the trench with? 

thanks for all your help crank case.


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## Jim F (Mar 4, 2010)

They sell a 3 or 4" diameter PVC pipe that has holes along the bottom in pairs. I don't know what they are called. You would dig your trench, line the bottom with a shallow layer of stone, place that pipe in with the pair of holes along the bottom so they don't fill with stones and then back fill around that with more stone.


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## concretemasonry (Oct 10, 2006)

If you use perforated pvc, it could easily be crushed unless it has the right cover, bedding and side fill if cars will be going over it.

Dick


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## crankcase (Sep 21, 2010)

They make perforated sewer pipe in 4" which is made for a septic drain fields, it's pretty thin walled, so you want to line the bed or bottom of the trench with pea rock then back fill with some larger stones, maybe something like 1- 1.5" river rock.


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