French drain around slab?

[rarebreed]

Has anyone put in a French drain around their slab for drainage away from the foundation? It looks like I'm going to have to do this as my new garage is at the same level as the driveway and surrounding soil which is allowing rain water to come in under the walls. Contractor suggested a French drain around the perimeter and need to know how it's done.

 

[1jjpop]

I don't know why it wouldn't work . Maybe cut a small ditch [vee type] and put some small intakes & dump into french drain.

 

[LB-1911]

My French Drain and Dry Well Project
http://www.garagejournal.com/forum/showthread.php?t=313369

 

[naturalgas]

I did. It was fairly easy. Did mine at the footing before was back filled . A six wheeler of stone, ten lengths of schedule 20 perforated two solid schedule 40 , 100 " of landscape cloth. My Kubota bx25 made it very easy ,no heavy lifting.


Sent from my iPad using Tapatalk

 

[myredracer]

Why not use perforated PVC, drain rock and filter cloth? Gotta dig and install gravel anyway. A french drain *could* eventually clog up. Where would it be drained to?

 

[DTE]

You need to have enough pitch in the drain pipe for the water to run out the end, and like said earlier filling the ditch with all stone will let it work better and last longer before clogging up. This is a photo of mine coming out from the building. This was installed against a foundation wall but putting one around a slab would be the same other than there would be no waterproofing involved.

 

[Diesel Dan]

I have a French drain on two sides of my barn.
Neighbor down hill from me has two rows of French drain to intercept the surface run-off from my property since he build his barn too low.

French drains are fairly common in areas of heavy clay soil.
In fact our septic system drain fields or mounds have to have a complete perimeter French drain system.

 

[gnpenning]

At the ends of my drains I put in large dry wells with 10yds of drain rock. Depending on your soil you need a place for the water to drain. If you had great drainage you wouldn't need french drains.

 

[theoldwizard1]

Actually, the best solution is add sand/gravel and raise the whole area at least 6" before the slab is poured.

You can also install a trench drain just in front of the garage door and connect it to the rest of the French drain. This will help keep water from coming in under the door.

Gravel only MUST be completely wrapped in heavy duty landscape cloth to keep the "fines" out of the gravel bed. If not, it will eventually complete clog.

The most important thing is proper pitch on the pipe for proper flow to the outlet. If there is no natural occurring low area for an outlet sloped AWAY from the garage, you can install a dry well. A dry well needs an overflow.

 

[finn]

They quit allowing structures directly on the slab, without a course of block or equivalent concrete many years ago around here for exactly this reason.

The heavy winter snow cover and subsequent spring melt makes it even worse.

A french drain may help in warm weather, but will have little effect when the ground is frozen and spring runoff begins.

Regrading is the only solution, in my opinion.

 

[Diesel Dan]

A curtain drain will help keep sub-surface water away from the building as well.
The curtain drain for our septic fields has to be 12" wide and min 16" deep. Our frost line isn't quite as deep as the U.P. but will go down 24" at times.

 

[theoldwizard1]

They quit allowing structures directly on the salb, without a course of block or equivalent concrete many years ago around here for exactly this reason.

The heavy winter snow cover and subsequent spring melt makes it even worse.

A french drain may help in warm weather, but will have little effect when the ground is frozen and spring runoff begins.

Regrading is the only solution, in my opinion.

Re-grading, especially raising the area where the slab will be, IS the best solution.

I don't get the "snow pack" you Yupers get, but mine DOES help with spring snow melt.

 

[brownbagg]

dig a trench fill with sand or gravel, drain it to day light, and no it not going clog up

 

[rarebreed]

The garage is already built, do no going back now. Just need to remedy the problem by putting in the drainage. Trench with gravel and perforated drains will likely be the answer

 

[NUTTSGT]

The garage is already built, do no going back now. Just need to remedy the problem by putting in the drainage. Trench with gravel and perforated drains will likely be the answer

Do you have gutters and down spouts ?

 

[myredracer]

Drawing showing perimeter drainage (separate foundation/footing). Rigid PVC would be better than the Big O in the drawing. Gravel can extend up to grade level but filter cloth shouldn't be exposed. Installing a "two pipe" system with a separate pipe for the downspouts can help a lot. And of course, the drain pipe away from the structure needs to have positive slope to wherever the water drains to.

 

[csp]

Contractor suggested a French drain around the perimeter and need to know how it's done.

If your contractor had done his job correctly there would be positive drainage away from the slab without a French drain.

I complain when I'm building about the drainage requirements we have to meet, and then I see threads like this.....

 

[fnieto]

For the front portion to keep water out from coming in under garage doors I formed up and used grates (fork lift traffic). You could design something similar and lighter to suit your needs. The end goes under ground some 70' to leach in.The total slope was 3" in 40' Also mentioned previously, rain gutters for the sides will work well with the in-ground drain system you choose.

 

[rarebreed]

Well, the building contractor is not the one at fault, it's the concrete contractor that should have paid more attention. Instead of bringing in fill, they dug down 4" from the lowest point of the driveway and to make the new slab even with the old driveway for a smooth transition. They didn't realize until after it was poured that the existing driveway was over an inch higher on one side than the other. Of course the day the framers were there starting the walls, the owner of the concrete company was there to look at the issue and blamed it on his workers for changing the pour schedule. He advised if they had not changed it he would have seen the issue before the truck arrived for the pour.
They had to cut back the old driveway 2 ft and install a drain in front of the garage door and slope the concrete down to keep the water from running under the garage door. I'm not as concerned with that as I am with the grade being higher around the side walls. I'm going to bring home a mini ex from work over New Years and dig the trenches for the drains and hopefully use the doser blade to grade down the high spots.

And yes, there are gutters with downspouts, one on the right front pointing out to the side and one on the left rear pointing out to the back yard.

I'll have to get pics and post the up here to show what I am dealing with.