Footing, slab, and stem in one pour?

[bdresch]

I have an old garage at the house I just bought that I want to fix up. It's 20x20 with a 20x15 room at the back. The room has no slab, only some uneven asphalt. None of the garage has a footing and the bottom plate and bottoms of the siding are starting to rot. I plan to jack up the garage and put in a proper footing and an 8-12" wall to raise the garage. I'm trying to figure out the best way to do this. Is there any way I can do this in one pour, I only need the slab in the 12x20 room, the 20x20 slab is fine? Would it make more sense to pour the slab and footing and then raise the garage via cinder blocks? Do I pour the footings and wall in one pour and then come back later to pour the floor?


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[DougWil]

The easiest way, is to move your garage over to your new footing if you can.
Or temp. move the garage out of the way.

If you have to do it in place, it is a chore to excavate, form and pour all while under a wall that could fall on you.
Simplest is to pour a reinforced footing with #4 L bars sticking up every 32" OC.
If you have nice soil you won't even need forms, rocky cave in soil you will.

Then CMU block stem wall from there up.
All CMU cells below grade should be filled with grout (pea gravel concrete) afterward, but I would fill them all.
The top course of block should have a horizontal bar around the entire perimeter.

http://planmyhouse.com/wp-content/uploads/2013/12/SD1_2_16_1.jpg
^ I would have at least 1 course of CMU above your finished slab to keep any water away from the wood wall.

 

[matt_i]

With a trenched footing/wall, you could do a monolithic pour of slab and walls in one shot. Armed with rebar that you set while the first pour was wet, build a single row of concrete block to get the bottom plate wood off the ground. And, while you're at it you might as well replace the bottom plate with treated wood. Large amount of work you are biting off there.

 

[bdresch]

The slope of my yard makes moving the garage off the spot pretty tough. Not too worried about lifting it, I'm a structural engineer. I just would like to minimize the time it's in the air. I'm thinking the soil is pretty sandy based on the speed that my snow melt water is disappearing. I have a friend of a friend who is a mason so I will have him come give it a look soon. The wife was thinking just start from scratch, but the structure and roof are sound so sticking $20k+ into a new structure doesn't seem right.


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[DougWil]

The slope of my yard makes moving the garage off the spot pretty tough. Not too worried about lifting it, I'm a structural engineer. I just would like to minimize the time it's in the air. I'm thinking the soil is pretty sandy based on the speed that my snow melt water is disappearing. I have a friend of a friend who is a mason so I will have him come give it a look soon. The wife was thinking just start from scratch, but the structure and roof are sound so sticking $20k+ into a new structure doesn't seem right.


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Sandy soil means a big wide footing trench and loss of support under the existing slab perimeter.

Lifting it isn't the problem, the problem, hassle and expense is going to be excavating and building a foundation in place.
A backhoe could excavate that small footing in an hour or two. Weeks will be spent digging, picking and shoveling by hand, all with that wall/building in the way.
Ditto forming, pouring, laying up a CMU stem wall.

And unless you have a lot of steel beams, larger wood beams and blocking laying around you will have all those costs in keeping the building safely elevated while you work.

I suspect putting a footing underneath it in place and fixing the rot issues will not be a financially viable alternative to new if you can't move it out of the way.

 

[bdresch]

I guess maybe my wording was incorrect in my original post. Local building code only requires are thickened edge slab on garages this size. My thought was not to go down for a full footing below the frost line. Would something like a thickened edge slab with a 8-12" wall be do-able in 1 pour? For the front portion of the garage that currently has a floating slab, do I have to dowel into that?

Thanks

 

[hoho98925]

Yes it's not too hard to do. Your slab edge form goes to the height of the top of your wall, the inside wall form is usually snap tied to the exterior edge form, and beveled on the bottom to give a good clean finish. You pour the perimeter of the slab and a few inches up into the wall form, pour the rest of the slab which allows time for the perimeter to firm up, then finish placing the wall concrete.

 

[James-W]

Any particular reason why you don't want to pour the footing below the frost line? I don't know that the cost difference would be all that much more but I think you would better off in the long term. It couldn't hurt to check into the cost before deciding.

 

[DougWil]

For the front portion of the garage that currently has a floating slab, do I have to dowel into that?

I wouldn't.

If you are going to have settlement and maybe frost heaves from a shallow footing you don't want to transfer that to the existing slab via dowels.

Please keep us updated when you start getting proposals to do the work.
I am curious about the cost of doing it with the garage in place.

 

[bdresch]

Any particular reason why you don't want to pour the footing below the frost line? I don't know that the cost difference would be all that much more but I think you would better off in the long term. It couldn't hurt to check into the cost before deciding.

I'm going to look into all options I guess. I was basing the floating slab thought on the fact that the garage has been standing for 20+ years without a footing and assuming I was going to have to hand dig under a lifted building I didn't want to have to go down 3+ feet.


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[James-W]

I'm going to look into all options I guess. I was basing the floating slab thought on the fact that the garage has been standing for 20+ years without a footing and assuming I was going to have to hand dig under a lifted building I didn't want to have to go down 3+ feet.


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Many years ago one the neighbors we had decided to fix his garage floor because it was all cracked and crumbling. He had a bunch of helpers and he was able to lift the garage up about 18 inches by using jacks and then he backed a trailer inside the garage that was fairly low to the ground. He then proceeded to move the garage so that the concrete floor was all exposed and he could break it up into chunks and remove it. Then he got a concrete crew to prepare the ground for new footings and a new floor. Once the concrete was done and cured he moved the garage onto its new home. It worked out well for him, possibly you could do something similar.