I need to learn tile drainage basics

[iowabucks]

Hey everyone. I have a 1000 sq.ft., 34'X28' garage 90% built on a floating slab here in Iowa. It is a detached garage built in my backyard. The yard has a bit of a slope from the back to the front of my lot.

My contractor/friend, (I know, should have never went that route), has been pretty much AWOL this last couple weeks so I need to learn how to do this tile job in case it comes down to me doing it.

My garage slab has been showing signs of ants, and water coming up through the cut lines with our recent heavy rains. I eventually want an epoxy floor so i'm hoping this tile drainage system will help that. I should have made sure the concrete contractors put down a vapor barrier, but I wasn't on top of that one.

I'm pretty sure I got the basics, but my google searches and forum searches don't really bring back the results i'm looking for. Can anyone give me any tips on what I need to be doing right for this to work?

I want my future gutters to be tied into the tile and have it all run downhill to the sidewalk or street in front of my house.

Around the backside of my garage slab, does the height of the tile need to be below the floor level of the slab? I do know that the trench needs dug deep enough to have a gravel base under the tile. And that it needs sloped accordingly for proper drainage.

I like doing projects like this on my own, but I want to make sure I know what i'm doing before I start. Any help would be greatly appreciated.

The backside of the garage is 3 blocks high, with grade being just below that. I have already been seeing plenty of water seeping through the blocks whenever we have a heavy rain. Definitely going with a block waterproofer on the outside. Now i'm regretting not going with a poured wall. This picture is the best one I have at the moment showing the grade and driveway placement. The garage is already built at the end of that driveway. The tile is going the length of the backside of garage and then down the left side of the driveway all the way to the sidewalk out front.

 

[matt_i]

First job in my opinion is to establish the location of utilities with Miss Dig or the like. It doesn't look like you have much room either side of the driveway.

If I understand the pics correctly it looks like you are already at a disadvantage of being lower on the hill than the house behind, so you have to manage stormwater you get from them.

As you said, all land around the garage somehow has to slope downward to get surface water moving away. In the back, I'd try to dig it out so that the ground right next to your back wall is sloping downward, starting from a plane that's the same level as the slab. In other words, unbury any block from the wall.

Next advice I have is to use a "silt sock" on any perf pipe you place in the ground, even if its in pea gravel. I think its a good idea to get a long lasting job and not one that fills up with soil fines after a couple of years.

I have 2 areas on my property where I'm planning to bury the gutter-flow for a ways, here its fairly flat. But, I plan to use Sch40 PVC for the part where it might see any vehicle traffic. Like not regular vehicle traffic, but an event like: I want to drive the pickup around with a load of shredded bark once every 3 years and don't want it to collapse the soft ABS. There may be different grades of corrugated pipe but what I have as a temporary overground measure is so soft. There is also the issue of freezing weather and times when there could potentially be ice buildup inside of the pipe, I feel like the PVC being smoother gives the ice less "tooth". Maybe that means it all will run to the end and jam up there I don't know for sure yet. But definitely "freer-flowing". There is the issue of managing transitions from square gutters to round pipes and I haven't worked that out yet. Probably will be something machined from plastic.

 

[LB-1911]

Give theoldwizards1 thread a look -

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

What is the distance from the back of the garage to the street?

 

[JDMopar]

I would run 3" pvc all the way from the back corners of both sides of the garage, down both sides of the driveway, all the way to the street. PVC is easier to keep the slope going in the right direction, and is well worth the slight cost difference. You could also tie your house gutters into it on that side of the driveway. Another added bonus is the water runs away faster in the pvc. As far as the water problems behind the garage, I would dig down all the way across the back wall to a point 12 to 18" below the slab. clean the dirt off the blocks, and coat it with Thoroseal. Let that dry, and then coat it with black mammy. Add some corrugated pipe in the bottom of the ditch that ties into the gutter drain, and backfill with washed 3/4 gravel all the way to the top of the ditch. The water coming off your roof is causing more problems than the water on the ground, unless there is a lot of run off from the neighbor behind you. I used pvc for my gutter drains on my garage, and am glad I did. The only thing I would do different now that I know better would be to use the big gutters instead of standard size. Good luck, and nice garage!

 

[bczygan]

I don't know if you are allowed to dump it in the street.

There may also be a prohibition against tying it into the sanitary sewer or combined sewer system.

Many places require you to keep it all on your own lot.

So the least I would do is take roof runoff as far from the building, and downhill with downspouts kicked out a ways. May need a cistern or holding tank, or at least rain barrels. Do some calculations to see how much you need to accommodate. How permeable is your surface soil and what are your subsurface conditions.

This is why there are more and more rules about how much hard surface you are allowed on your site. Water has to go somewhere, and cities don't want yours, to have to deal with and treat.

Bill

 

[MagKarl]

I would run two lines, one perforated 4" PVC at footing depth, and a second solid line that your downspouts dump to. I use fabric to line the trench and wrap the line and drain rock as it's more filter area. I'd run drain rock full depth against the block wall. I prefer drilled PVC to the corrugated sock type but anything is better than a wet building.

 

[kbs2244]

That is a lot of roof.
Go oversized on the gutters and downspouts.

 

[matt_i]

I don't know if you are allowed to dump it in the street.

I lived the first 10 years of my life in Iowa City, it was very common in the large sub where I lived to have yard pipes from sump pumps (stormwater, etc) going to the street, the curbs were cut and repoured to enclose the pipe. I can't speak to codes, too young to have known any of that.

The majority of my life has been in Michigan I've never seen one

Still a good idea to check. Its not functionally much different than pouring it on the driveway and then using curbs to channel it down to the street.

 

[iowabucks]

What is the distance from the back of the garage to the street?

It is about 100 feet from the street to the back of the garage.

If I go with oversize gutters and downspouts, would 5" tile be large enough to handle the runoff from the roof?

I still need to check with the city, but I believe it has to dump before it reaches the sidewalk.



Here is a picture of the backside of the garage. It's already dug out pretty good as the yard did slope up in the back. Shouldn't need a lot more digging done. I wasn't sure at what depth the tile needs to be at. I'm sure it needs to be slightly below the slab floor level, but I may not be able to go quite that low to be able to slope all the way around the back and down to the street. If there are some areas where the tile is not quite lower than the slab, will it still be effective enough?

With pea gravel under and on top of the tile tube, should I continue to run the rock all the way up the backside of the wall? With the dirt being about 18" higher in the back than the slab floor I didn't know if that whole depth should be rock, or if the rock should be covered with dirt when finished?

Definitely also planning on coating the blocks with whatever was suggested earlier in this thread.

 

[P Dubya]

Iowabucks... In your last post you said you want to put peagravel under and on top of the tile. The tile will work better if you dig the dirt to grade and lay the tile directly on the dirt. Lets say you put in 6 inches of pea gravel first and then the tile then cover with more pea gravel. The water will have to build up to more than 6 inches before it will follow the tile. Think of the 100's of thousands of miles of farm drainage tile here in Iowa. No rock underneath it...

 

[iowabucks]

That makes sense. Don't know how I got that idea in my head. I thought I read it somewhere.

I would then go with a 4" tile along the backside and then down the side with two downspouts emptying into that. Then it would be a steeper shot down to the street. But with a heavy rain and lots of water going into the tile, would that cause any kind of vacuum issues on the upside or beginning of tile that is really only there for "seepage". (sorry, couldn't really think of the correct term there.)

 

[csp]

No, you're not going to be creating any kind of suction or vacuum. It's all open to atmosphere.

Don't make this harder than it needs to be. Water follows the path of least resistance. Create the path of least resistance.

 

[kbs2244]

Pea gravel is a common base for drain pipe.
Even sewage pipe.
All your big box "roof drains" are laying on pea gravel under the floor slab.
The reason is the ease of getting and maintaining the need grade.

You cannot have a low spots in your run.
Water will pool there and freeze in the pipe if it cannot run to dry.
If you need to have the high end above the freeze line to get that slope, that is OK since it will be draining dry.

 

[buddyboy]

if you have slope then liquid water will flow, it won't freeze. even if it does freeze so what? it's probably not raining it's snowing... when it melts it will flow again.

like others have said, put that pipe on top of the soil in the bottom of your trench, dig all the dirt away so that one side of your trench is your building.

when you put the pipe in throw a level on it, make sure you have slope and look for dips.

make sure the holes in the pipe face DOWN.

fill the trench with pea gravel

when it rains, water will flow through the pea gravel it will hit the bottom of your trench and then up into your pipe. if you put the holes on the top side of the pipe then the water will need to rise 4" before it goes into the holes. if you look at the pipe you'll see how the position the holes... they aren't on the bottom they are 10-15 degrees off bottom.

think of your trench around the garage as a big dry well the collects the water and the pipe drains your trench.

the trench that is not in an area that doesn't need drained can be back filled with fill/top soil