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View Full Version : O.T. Drainage question



Mike Amick
02-20-2019, 07:56 PM
I put a little shed on a cement slab. The ground is fairly level with the slab. I found out that
during a heavy rain, water will flow under the barn door.

So .. French drain pops into my head. I dig the ditch and realize that I don't really have anywhere
for the water to go. It's already at the bottom of the yard and right next to the neighbors fence.

That night it rained like hell, but the water in the ditch never came close to the level of the slab.
meaning .. just the ditch prevents the flooding. So I figure I would just fill the ditch with stone
hoping it would act like when it was empty.

I had already bought the drain pipe, a 4" rigid pipe.

Silly question I have is ... would putting the pipe in there anyways ... would that not help delay
the fill up ?

http://www.mikeamick.com/misc/shed_ditch.jpg

kev74
02-20-2019, 08:04 PM
If nothing else, the pipe will provide a bigger void for the water to fill and will require less gravel to backfill the hole.

rsal
02-20-2019, 08:11 PM
from my experience just putting in pipe will no provide any assistance. Pipe will probably float out (raise) until it is on top of the ground, Better just fill in with stone (use larger stone than shown in photo and cap with what you show) Due to your location, freeze-thaw will not be an issue so that will help some

A.K. Boomer
02-20-2019, 08:32 PM
Pipe won't do you much good you already have the situation improved, what I would do is increase the width of your stones and totally fill to the top with stone and then place those cement step pads on top, tons of surface area and yet not all "mushy" when you walk through or drag out stuff with wheels from shed...

reggie_obe
02-20-2019, 08:39 PM
Pipe would provide more void space than stone, so more volume to collect rainwater before the trench overflows.

A.K. Boomer
02-20-2019, 08:46 PM
It may be a trick of the camera but the ground to the right looks higher than the slab, with nothing to break up the slope the water would head in direction of the slab, creating a lower drainage area (like he did) just before the slab is a good way to go, adding pipe might buy you some time over just rock but will not increase the saturation area below, double width the trench and adding rock will both buy immediate time for flash flooding and also good saturation drainage for long hard rains...

Paul Alciatore
02-20-2019, 09:10 PM
I have installed French drains two times. One was along the edge of a building where I worked. The fair sized roof sloped down to that side and the rain water poured off in sheets. Another section of roof emptied onto that roof adding even more water to the deluge. The bad part was it was the "front" of the building and they had added a garden along this entire wall that was built up about 18 to 24 inches. So, it was a dam that held the water behind it and against the wall. They wondered why it leaked into the offices, including the GM's.

I dug a trench and filled it with loose gravel. I ran two drain field pipes in it, one for the first half and the second for the other half. Drain field pipe is drain pipe with holes drilled in it. In this case it was to allow the water to enter into the pipe. The end of those pipe runs was run under a walkway (another dam) into the parking lot where it discharged. They laughed. But when the first big rain storm came, the water poured out the pipes into the parking lot and the offices were bone dry. It has been over 25 years since that installation but I occasionally drive past that building and if it is raining, I drive into the parking lot. The system is still working well today. The water still pours out into the parking lot as fast as it falls behind that elevated garden.

The second one was in front of my Florida home. The drainage was a supposed to be via a shallow ditch near the edge of the road that they called a swale. Over the years the owners had built up their lawns above street level so the water could not flow along that route. However my drive way, including a semicircle, was installed according to code and followed the outline of the past tense swale. So when it rained, the rest of my driveway, the street and parts of the lawn drained into these depressed areas of the driveway forming a couple of lakes that took days to completely dry up.

I dug three trenches across the island formed by the semicircular drive and installed drains at each side at the low point, next to the driveway. Again I used drain field pipe in the trenches. Normal drain pipe and fittings were used leading from the drains to the trenches. I put crushed stone below and all around the drain field pipe. I probably had about 45 feet of it in all. When it was done, I never had more than a small puddle at the edge of my driveway even after a heavy rain.

My point is, the drain field pipe (perforated pipe) is an essential element of a French drain unless you do not expect to conduct the water away. And, when properly done, they do work. They work very well. Yours looks a little small to me, but then, it is a small building so it may be enough. You can always add more later.

PStechPaul
02-20-2019, 09:23 PM
You might consider jacking up the shed 4" or so and putting it on a few 4x PT timbers or railroad ties. You might then need to add a wood floor. Or maybe lay some 4x8x16 concrete blocks which would provide drainage and ventilation through the hollow cores.

A.K. Boomer
02-20-2019, 09:27 PM
You might consider jacking up the shed 4" or so and putting it on a few 4x PT timbers or railroad ties. You might then need to add a wood floor. Or maybe lay some 4x8x16 concrete blocks which would provide drainage and ventilation through the hollow cores.

This is of course problem #1, the slab was poured too low, you should always have to step up at least a little into a building not shuffle in at ground level...

Mike Amick
02-20-2019, 11:22 PM
Ok .. no surprises.

I truly wish I would have put at least one layer of block down with the wall bottoms on the block.

Tell ya what I did do though, I bought a 100' roll of 1/4" thick 10" wide rubber. Wrapped it around
a treated 2x4 with another treated 2x4 on top of that and the whole thing bolted down to the cement.

Leaks like a sieve ... ahahah .. And I thought I was being so smart.

AK has a point that it wouldn't hurt to make the ditch wider

I think I will throw the pipe in there to add to the void, but I'm not sure about the size of stone to put in.

To exaggerate the problem for a solution, If I put two giant stones in a bucket and fill it with water, I think
it will accept less water than with many little stones. Just guessing here. My knee jerk says its wrong but
my brain thinks that right.

A.K. Boomer
02-20-2019, 11:36 PM
To exaggerate the problem for a solution, If I put two giant stones in a bucket and fill it with water, I think
it will accept less water than with many little stones. Just guessing here. My knee jerk says its wrong but
my brain thinks that right.


Go with the knee jerk ...

I like that Shed - that's how Kazinski got his start lol seriously though cool weathered wood patterns

QSIMDO
02-20-2019, 11:40 PM
Install a dry well, 4' wide x 4-5' deep, soil fabric on the walls and filled with .75" stone.
Run your french drain in, cover with more fabric and at least 12" of top soil.

J Tiers
02-21-2019, 12:45 AM
QSIMDO has the answer.

The only issue you might run into is if either you have impermeable clay soil, or if the area you need to put the dry well in is so wet that water fills it normally.

If the soil is impermeable, the dry well won;t empty. If the area is wet, it probably will back up, but may then drain down to the normal level fairly quickly, unless the entire low level area fills up.

vpt
02-21-2019, 07:25 AM
Is it just a small slab for the shed? You could have the slab jacked up as well.

Tungsten dipper
02-21-2019, 07:52 AM
Imagine, having all of you in the kitchen at the same time, trying to cook one recipe. I hope there's a lot of wine.

lynnl
02-21-2019, 08:26 AM
Good point Tungsten. It's funny how many of this crowd always want to propose the most elaborate and complex solutions to a problem, especially at the price of someone else's money, or time, or effort. :D

Obviously the soil drains well, since the simple open 'moat' prevented the inflow under the shed.
In light of the infrequency of heavy rains in southern California, just go with a simple ditch filled with small stone or gravel.

vpt
02-21-2019, 08:33 AM
Good point Tungsten. It's funny how many of this crowd always want to propose the most elaborate and complex solutions to a problem, especially at the price of someone else's money, or time, or effort. :D


Personally I look at problems like this with different ideas in mind. Digging a hole and filling with rocks to me is a patch to the problem which may or may not work. Raising the whole deal above the problem is 'the fix'. All depends how much work/money each approach would take and how much more time/money/effort it would take to do the job right after trying the patch job.

Also a lesson to be learned here, don't pour slabs lower than the surrounding ground. lol

Abner
02-21-2019, 08:41 AM
Nice looking building! I don't understand how the door lays flat against the wall is there a toe roller?

The only problem I have had with french drains is they often fill with debris and dirt. Looking at your picture the soil to the right of you trench is higher and that will auto-correct over time and fill the open space in your french drain. I think your idea will work and perhaps you were planning on doing this anyway but that dirt must taper gradually and then you need something planted there to hold the soil in place. Rain will always move some dirt. They make and sell open troughs with grating. These are cleanable should the need arise. As already mentioned a dry well. 55 gallon plastic drums work super drilled with lots of small holes . My 2 cents

softtail
02-21-2019, 08:42 AM
It's not that hard in the big picture of things to jack it up and put a course of concrete block down on the slab around the perimeter then let the shed down on it.

If you stick with the ditch, make it as big as possible and yes get a perforated pipe in there, wrap it in permeable fabric to help keep out fines/silt, then surround in coarse gravel. Any ditch filled with gravel will eventually (fairly quickly) fill with dirt and stop working.

cameron
02-21-2019, 08:49 AM
.






To exaggerate the problem for a solution, If I put two giant stones in a bucket and fill it with water, I think
it will accept less water than with many little stones. Just guessing here. My knee jerk says its wrong but
my brain thinks that right.

Two giant stones in a bucket is not a very good model.

Think of a large room filled with basketballs. There is a large volume of void unfilled.

Think of the same room filled with 1/2" ball bearings. The voids are smaller, but they have the same shape and there are more of them. The total void volume is the same.

Fill the room with basketballs, and add as many !/2" ball bearings as possible. The void volume is much less but there's still room for a heck of a lot of 1/16" ball bearings.

If you want maximum drainage space use a single size stone, preferably rounded stone. Size doesn't matter much, except that smaller stone will plug up with organic matter sooner.

If you want maximum compaction, and smallest void volume, use a well graded gravel.

jdedmon91
02-21-2019, 09:03 AM
Question how hard would it be to create a grade around the shed? If you could just remove enough soil around the building to create drainage so the that water would run around and away from the building


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3 Phase Lightbulb
02-21-2019, 09:52 AM
I had a 6-8" deep base of 3/4" stone put down (landscaper dug it down 6-8" then filled with 3/4" stone). Then the shed's floor was built with PT joists that sit on concrete riser blocks.

I was originally thinking of either going Sonotubes or a slab foundation but the building department said I could use crushed stone which surprised me but it certainly does provide nice water drainage. I'm curious how true/level this foundation is going to remain after many winter seasons though.

http://www.bbssystem.com/pictures/newshed_10.jpg

jdedmon91
02-21-2019, 01:56 PM
I had a 6-8" deep base of 3/4" stone put down (landscaper dug it down 6-8" then filled with 3/4" stone). Then the shed's floor was built with PT joists that sit on concrete riser blocks.

I was originally thinking of either going Sonotubes or a slab foundation but the building department said I could use crushed stone which surprised me but it certainly does provide nice water drainage. I'm curious how true/level this foundation is going to remain after many winter seasons though.

http://www.bbssystem.com/pictures/newshed_10.jpg

What size is this building? Looks larger than mine that I have my shop in


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3 Phase Lightbulb
02-21-2019, 01:58 PM
What size is this building? Looks larger than mine that I have my shop in


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That's a Reeds Ferry 24'x14' shed.

jdedmon91
02-21-2019, 02:00 PM
That's a Reeds Ferry 24'x14' shed.

That’s larger than my shop, it was an over built 20’x14’


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MattiJ
02-21-2019, 03:29 PM
Imagine, having all of you in the kitchen at the same time, trying to cook one recipe. I hope there's a lot of wine.

This is going to be mac&cheese no matter how fancy italian wine you bring.

--
Sorry to rain your parade but build like that is doomed to flood because any amount of rain with smallest wind ends up to the concrete slab even if it would be 10" higher.
So just let it rot slowly. It's going to last quite a many years anyways.

3 Phase Lightbulb
02-21-2019, 03:35 PM
That’s larger than my shop, it was an over built 20’x14’


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My shed is just for storage. It's only purpose is to help keep bulky items out of my garage which is where my shop is. If I was building a shop, I would have definitely went with a real foundation/slab, insulation, HVAC, etc.

PStechPaul
02-21-2019, 04:06 PM
I'm looking forward to completing my 8'x12' shed project, now that spring is imminent - I'm watching 6" of snow melt in the sudden 60F southern breezes. It will be mostly for storage, but also perhaps a place to work on my mowers, lawn tractors, and other outdoor equipment. The original shed was impractical for that purpose.

http://enginuitysystems.com/pix/house/Shed_4349.jpg

http://enginuitysystems.com/pix/house/Shed_4351.jpg

But drainage was not a problem. The mower shed was also not very practical - it was a temporary thing built from scrap, but it was OK for 10 years or so:
http://enginuitysystems.com/pix/house/Shed_4385.jpg

Mr. Tibbs helped me dismantle the ugly things:
http://enginuitysystems.com/pix/house/Shed_4439_Tibbs.jpg

J Tiers
02-21-2019, 04:20 PM
Dirt filling up? A couple layers of the loose fabric that is made to prevent that will make it last decades. A hole with ricks in it, also lined with the fabric is hardly a fancy solution, but it works. I;d have it dug before you folks stop arguing about spelling.

As for filling up 10', that depends a lot on what is around it. Yeah, bottom of hill, OK, but is there lower land beyond for water to go to? Normally there is, or it would already be a lake.

3 Phase Lightbulb
02-21-2019, 04:31 PM
I'm looking forward to completing my 8'x12' shed project, now that spring is imminent - I'm watching 6" of snow melt in the sudden 60F southern breezes. It will be mostly for storage, but also perhaps a place to work on my mowers, lawn tractors, and other outdoor equipment. The original shed was impractical for that purpose.

http://enginuitysystems.com/pix/house/Shed_4349.jpg


Are you going to build the next shed closer to ground level for the entrance? I'm sure it would be much more practical if you could easily roll things in/out of it without having to navigate stairs/etc.

J Tiers
02-21-2019, 04:43 PM
Are you going to build the next shed closer to ground level for the entrance? I'm sure it would be much more practical if you could easily roll things in/out of it without having to navigate stairs/etc.

it's on a hill, remember? The other side of it is at ground level, per his comments.

3 Phase Lightbulb
02-21-2019, 04:45 PM
it's on a hill, remember? The other side of it is at ground level, per his comments.

After excavation into the hill of course

PStechPaul
02-21-2019, 04:51 PM
Yes, I will probably use the rough original upper foundation as a garden, and build the new shed near ground level, where I already have two rows of concrete blocks for what was going to be a 4' x 8' shed. I'll move (or remove) the small rough woodshed to get room for it, and I'll add another two rows of block at 4' intervals for 4'x8' floor panels. It will be just 8" or so above ground level, so it will be easy to have a ramp to roll equipment in and out.

http://enginuitysystems.com/pix/house/Shed_Base_4510_14ft_Stakes.jpg

http://enginuitysystems.com/pix/house/Shed_Foundation_4744.jpg

My original plan for a 4 x 8 shed:
http://enginuitysystems.com/pix/house/Shed2a_SW.jpg

flylo
02-22-2019, 01:34 AM
Use the pipe with holes in it a a mesh sock.turn the holes down. If the problem gets worse put a small sump pit at the low end of the pipe & a small sump pump evan a solar one if no electric. Problem solved!

Paul Alciatore
02-22-2019, 02:50 AM
So that's where the door should be?????

:rolleyes:




it's on a hill, remember? The other side of it is at ground level, per his comments.

Mike Amick
02-22-2019, 01:11 PM
Nice looking building! I don't understand how the door lays flat against the wall is there a toe roller?


Lol ... caught me. Because the barn door is set behind the rollers, yes, the bottom wants to swing out. I do have
a toe roller in the open position that really helps but as it closes it starts to swing out. I hate the look so when it's
closed I pull the door in and kind of latch it to avoid that.