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Old 03-07-2013, 11:13 AM   #1
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DIY Foundations Info?


I would like to research into building my a complete new 20ish x 20ish detached shop/garage.

I am set with the framing and finishing process as I have experience with that, but I am most lost when it comes to the complete foundation, from breaking ground to finishing it all off... I understand frost depths, anchorage (both shear and uplift), and reinforcing, but I think my issues comes into how much to dig out, how to prep, how to form, ect..

And then I question mono-pour vs 2 stage pour.. floating slab vs structural slab (thickened edge slab footing)...

Can anyone recommend any books or websites on the subject?

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Old 03-07-2013, 09:04 PM   #2
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Slab by itself is not a good base for taking the wall and the roof loads. You need some kind of footing. Shallow footing with insulation is easy way but the earth under/around the concrete can not freeze/thaw. This means heating the garage constantly in winters.
If you must have a concrete floor, to store cars, you must dig down to the frost depth of your area.

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Old 03-07-2013, 09:20 PM   #3
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[QUOTE=carpdad;1132143]Slab by itself is not a good base for taking the wall and the roof loads. You need some kind of footing. Shallow footing with insulation is easy way but the earth under/around the concrete can not freeze/thaw. This means heating the garage constantly in winters.
If you must have a concrete floor, to store cars, you must dig down to the frost depth of your area.[/QUOTE]

Not true at all, the vast majority of garages here in that size are on floating slabs, no frost protection at all. Trust me, if every garage that size required a full frost foundation, I'd be much better off financially, but it just isn't the case.........
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Old 03-08-2013, 09:23 AM   #4
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Slabs do not need to be frost protected in my area, you can pour them directly onto the earth, footings need to be protected minimum 12".

I was thinking about doing something like this, but I am not sure how to handle water drainage as code requires 1/4" per foot, but maybe that would not be required for a detached garage?? I was also worried about settling and the slab cracking where it meets with the thickened area..

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Old 03-08-2013, 01:10 PM   #5
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that's poifect ! its called an ' unipour ', ' monopour ', turned-down edge ', or ' thickened edge ',,, what a beautiful drawing - did you do it yourself ? you're my hero !
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Old 03-08-2013, 01:40 PM   #6
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Originally Posted by cbzdel View Post
Slabs do not need to be frost protected in my area, you can pour them directly onto the earth, footings need to be protected minimum 12".

I was thinking about doing something like this, but I am not sure how to handle water drainage as code requires 1/4" per foot, but maybe that would not be required for a detached garage?? I was also worried about settling and the slab cracking where it meets with the thickened area..


That's the way to go,now add a 6" high x 4" wide curb all the way around the slab,with the exception of the service door and overhead door,and your done.
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Old 03-08-2013, 01:50 PM   #7
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What is the reasoning for the curb? And is it done as a second pour?
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Old 03-08-2013, 02:34 PM   #8
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The reason for the curb is to get your sheathing and siding up above grade and run the curb level while you slope the floor to drain toward the OH doors. You dont want to frame off a surface that is not level. A triangular piece of wood trim should be put on the inboard side of the form for the curb so you end up with a canted edge. We used to call this skewback.

I would pour the curb with the wall and form the wall with a ledge on which to pour the slab. I would put expansion joint around the three sides of the slab that are captured. I would reinforce the slab with No 4 rebar, and put 4 piers evenly spaced in the middle of the slab, put 4 inches of clean stone, vibra-plated in the slab and then pour a 6 inch slab over poly. This will support autos.
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Last edited by jagans; 03-08-2013 at 02:40 PM.
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Old 03-08-2013, 05:49 PM   #9
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What is the reasoning for the curb? And is it done as a second pour?

You can do it either way,but we always did a monolithic pour, if you do 2 pours it would be a good idea to add rebar every few feet to tie it to the slab,don't forget the anchor bolts and no expansion joint is needed that i can see.
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Old 03-08-2013, 07:38 PM   #10
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Hi Canary,

How deep do your footings need to be in FL? Its 40 inches here. Never mind, I see its 12 inches. We need expansion joints here also. This is why JoeC keeps asking people to put in their location. This should be mandatory. Are there an Moderators out there listening?????
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Old 03-08-2013, 08:45 PM   #11
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Quote:
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Hi Canary,

How deep do your footings need to be in FL? Its 40 inches here. Never mind, I see its 12 inches. We need expansion joints here also. This is why JoeC keeps asking people to put in their location. This should be mandatory. Are there an Moderators out there listening?????

He doesn't need footings, it's a floating slab.
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Old 03-09-2013, 07:35 AM   #12
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He doesn't need footings, or expansion joints on a garage this size, no matter where it's located, control joints will suffice..........

cbzdel, the reason for the curb is to keep the lumber above the exterior grade to keep it from rotting as easily, as well as it allows the floor to be pitch while still allowing the outside curb to be level.

I wish I had a picture of one, we do several a year with curbs, because it's pretty hard to explain how to form and finish them. Do you want a level slab, or do you want it pitched to a drain/the OH door?
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Old 03-11-2013, 10:07 AM   #13
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Could I just put the top of finished slab 6" above grade and call it good?

Personally I would prefere a flat slab, but maybe thats not really want I will want in the future? On vehicle will be parked in it.. Funny thing is my parents have a 2 car garage, 24x20 and they did a footing/stem wall/ with seperate sloped slap. I went in there one day after the rain, and the rain was just pooling under their cars not draining away.. So really is 1/4" even enough to drain auto rain runoff?? I guess maybe if there is several inches of melting snow on the vehicle then it might be different??
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Old 03-11-2013, 02:30 PM   #14
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It's your call as to how you want the slab to be poured,we are just trying to give you the best information out there to save you grief down the road.
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Old 03-11-2013, 02:59 PM   #15
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cb....click on the 'garage build' link in my signature......I built a 20x25 garage about 5 years ago...single pour with a 8" stem wall around the perimeter.....(keeps the water out).....

Based on what I learned.....hire a foundation guy to do most of the work....yea, you can do the excavation and rebar....maybe even the forms....but when it comes time to pour....that is not something you want to do yourself the first time.

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