French drain construction

[Hollywood D]

I need to put some sort of French drain on the back end of my detached garage. The last two strong rains we have gotten here, the water has gone up under the siding and it's running on top of the concrete wall and then into the garage. The ground in the back slopes down towards the building and it's only 6" above grade (which is code here). I plan on digging it out some so there's more concrete above grade. It seems like I need to put a drain in there though.

I'm thinking French drain, unless there's a better idea. My question is, the point where it would terminate is level ground. So, can I terminate this thing below ground or does the end of the pipe need to be above grade? Seems to me it would need to terminate above the grade so there's pooling issues underground or inside the pipe. I can do it either way easy enough, just not sure what the best way to do it is.

 

[myredracer]

First, what is the existing soil type and does it perc well or not? Small lot or rural? Is there any point on the property lower than the slab elevation?

 

[theoldwizard1]

I had the EXACT same problem. This is my solution

My French Drain and Dry Well

The water has to go somewhere below the level you want to control it at. The dry well works but maybe twice a year it overflows. I use a 1/10 hp "paddle" pump to lower the level below the ground. I could probably just leave it and it would "cure" itself in 2-3 days.

BTW, my soil is mostly clay.

 

[Hollywood D]

The soil has clay consistency but there's also a lot of decomposed granite underneath. I can dig 6 inches and hit pretty hard rock. It's a rural lot. The only spot on the property lower than the slab would be in front of the garage, at the driveway. I'm at 8300' in the mountains so we get these freak rain storm once in a while that dump so fast, the soil can't absorb it

 

[Radix2]

French drains are a waste of time mostly..

When the ground is frozen or saturated, they don't work. After years of normal outside matter falling n the ground (leaves, grass, etc. ) the infiltration becomes slower and slower as small particles clog the filter.


The purpose of a French drain at best is long term dewatering of a saturated spot, not to control downpours anyway.

If a solution is possible, it is to do as you suggest- regrade to get the water to flow away from your building. Works in any weather, works forever.

You have to have slope and an outflow of your drain pipe in any case.

 

[Hollywood D]

I had the EXACT same problem. This is my solution

My French Drain and Dry Well

The water has to go somewhere below the level you want to control it at. The dry well works but maybe twice a year it overflows. I use a 1/10 hp "paddle" pump to lower the level below the ground. I could probably just leave it and it would "cure" itself in 2-3 days.

BTW, my soil is mostly clay.

Good info there. My situation is pretty similar to yours. I may be able to terminate it above ground, I'll have to do some thinking

 

[Chaznsc]

Sounds like to need a swale and not a french drain. The FD is useful in deterring ground water, not surface runnoff.

 

[Bretny]

If you have high clay content most of the problem could prob be solved with proper grading away from the building.
Do you have any pictures of the area?

 

[theoldwizard1]

If you have high clay content most of the problem could prob be solved with proper grading away from the building.
Do you have any pictures of the area?

On small suburban lots you can not always grade away from a building. Or if you do, you wind up with a "bowl". It you are on top of clay, 4"-6" can sit there for 3-4 days after a heavy summer thunderstorm.

French drain AND a dry well ! (See my link)

 

[LandofRath]

Curious.. does the garage have gutters? if so where to they go?

 

[Philbert]

Do the French drain then have a trench for any over capacity away from your building fill it with gravel and the water will drain away from the building to share ever you desire the water to go through the trench. You dont have to make it deep, just enough cor the water to move maybe 6 to 12 inches

 

[theoldwizard1]

Do the French drain then have a trench for any over capacity away from your building fill it with gravel and the water will drain away from the building to share ever you desire the water to go through the trench. You dont have to make it deep, just enough cor the water to move maybe 6 to 12 inches

If you do not have a low spot that will hold a LOT of water, you need a dry well. See the link in my previous post.

 

[Hollywood D]

The gutters drain off the sides at the front. This issue is in the back of the garage.

 

[ptgarcia]

There really isn't enough information for anyone to give a real solution, but an infiltration trench or drywell or combination of both are easy to construct and usually effective. They both provide a place to store water until it can infiltrate into the surrounding soils, and if the infiltration rate is slow where you are they can at least keep most of the water off the surface until you can de-water after the storm passes.

 

[Lynden]

Sounds like to need a swale and not a french drain. The french drain is useful in deterring ground water, not surface runnoff.

I agree. Can you post a picture of the area?

 

[scooby074]

Pics would help. But likely the first thing Id do would be pull the slope back from the back of the garage and install a swale to move the water away from the back (unless it already is). The easiest option is to just make the water go somewheres else with landscaping.

After that, Id start the cheapest route first, thats a french drain. Well done, with a good pitch and good 3/4 clean stone in the trench can move a lot of water. Dont go with the Big O style flex pipe, go with perforated rigid 4" "sewer" PVC pipe. Also line the trench and over the pipe with landscape fabric to keep the fines out. If the front of your garage pitches away from the house or garage area, Id likely daylight the pipes there. Sounds like you really only need to move the water from the back of the garage to the front.

If that doesnt work, Id put in a proper catch basin at the back with a manhole cover on it to hold the rush of water and let it gradually perc through the rest of the existing french drain. Cost would be significantly higher for the crock/catchbasin option so it would be a bit of a last resort.

 

[brownbagg]

where you terminate it,just dig a decent pit and fill with gravel

 

[marineman]

I think the OP and most people suggesting a french drain really mean curtain drain but either way I'll say either swale or curtain drain. A french drain is a waste of time like someone mentioned, they're deep and intended to control ground water. A curtain drain is the same thing much shallower to control surface water. If you don't have a decent slope just run it to a dry well, without seeing the site or the soil just make it as big and as deep as you can.

 

[jonshonda]

pics please

 

[theoldwizard1]

pics please

My French Drain and Dry Well

 

[Hollywood D]

I’ll try and grab pics tonight or tomorrow

 

[kbs2244]

Running downspouts the length of the garage would be a whole lot easier and cheaper.
Get the water before it gets to the ground.

 

[ptgarcia]

Running downspouts the length of the garage would be a whole lot easier and cheaper.
Get the water before it gets to the ground.

And do what with it?

 

[Hollywood D]

I finally got pics today. We had a really bad rain last night. Enough that it caused a mud slide on the highway. More water infiltrated the garage again. I tried to capture the slope as much as I could. I also found some hairline cracks in the concrete but unable to tell if they go all the way through. I already dug out a little bit of a swail and it was working last night. A steady stream of water was running down it. It’s not water from the gutters, they empty out on the opposite end.

This building is new so if it’s actually coming through the concrete rather than over it, that will be a warranty issue with the contractor.

The third picture shows the spot where the wall is lowest and I suspect it’s coming through. The interior pictures show where it’s running down the wall. The siding on the inside is not wet though. I sprayed that yellow foam in that gap because you could see daylight through it. I did that to help make it air tight and keep bugs out.

 

[scooby074]

Pics help a bunch.

First Id drop grade around the rear perimiter of the building, then Id do some pretty aggressive contouring in the area between the branch pile and the back of the building to get the water going around the building. Lastly Id do the french drain (with pipe) up close to the building to keep the area dry.

 

[Hollywood D]

Well we had another heavy rain tonight. I had a chance to go out into the garage and watch. Turns out the water is coming through the foundation, not over the top like I thought. I’ll be contacting the builder on this one.

 

[Bretny]

French drains or any type of drain really work better when discharged to daylight. If you get frezing temps a drywell or pump system really isnt ideal.

You cant grade around the building better? It looks like you have alot of room to properly grade around that building. Adding infrastructure that will most likely fail wouldnt be a good selling point.

 

[ptgarcia]

French drains or any type of drain really work better when discharged to daylight. If you get frezing temps a drywell or pump system really isnt ideal.

You cant grade around the building better? It looks like you have alot of room to properly grade around that building. Adding infrastructure that will most likely fail wouldnt be a good selling point.

You have to be careful, though. Without some sort of agreement (easement, right-of-way, etc.) you can divert concentrated flows to another lot/parcel. You need to mitigate your own water.

 

[like2wheel]

Not sure I follow why you think it's the builder's fault

 

[Bretny]

Looks like hes got plenty of room for some swales thst flstten out past the building. Flattening them out after the building wont make a consentrated flow..but a french drain would.

 

[Hollywood D]

I could rent a bobcat and work on the grade, or have someone come do it.

 

[Hollywood D]

Not sure I follow why you think it's the builder's fault

Thought it might be a warranty issue since the building is under a year old

 

[strutaeng]

I could rent a bobcat and work on the grade, or have someone come do it.

I'd lobby for this option.

Do you have like 20' of property uphill from the building? I see a chainlink fence not too far from the building.

If you didn't have civil drawings I don't think you can go to the builder. How was he supposed to know where to set the elevation of the building? Unless you brought up the issue during construction. Call him and maybe he can be nice about it and do the work. Otherwise just pay someone with a tractor. It's probably less than $500 for this work to regrade.

You have plenty of fall and land to regrade. Avoid drains if you can simply due to maintenance that you have to keep up with.

 

[Hollywood D]

That chain link us just a dog run. There's about 50' up from the back of the building. I contacted the builder because the water is coming through a crack in the foundation, not for the grading.