Building garage over existing slab

1830 Views 13 Replies 8 Participants Last post by Nealtw, May 25, 2020

MittensCat

Discussion Starter · May 24, 2020

I have a 25' x 18' concrete slab that looks to be about 4 inches thick that used to be a garage floor. I think the concrete was poured over top of an original slab because the concrete formed around the studs. My dad and brother and I demolished the garage too long ago for me to remember what it looked like.

There are some large cracks and uneven segments in the slab. I'm not sure how stable the slab would be for attaching a bottom plate directly onto it. I was thinking that I could build a structure similar to the pole barns I've seen constructed on youtube. My thought being that I could cut the slab and pour columns or footers of concrete to support my posts. I'm trying to avoid removing the slab and pouring a new one because it's expensive and might not add enough value to the home to justify it.

I'm attaching some pictures so that you guys might get a better idea of what I'm working with.

My questions are:

-Does my pole barn idea to retain the slab for a floor make sense?

-What dimension of lumber would the poles/posts be and would they be treated?

-Would it be possible to anchor a bottom plate directly to the slab? If so, I imagine it would need to be a treated 2x. Would the studs need to be treated as well?

Thanks for any advice and let me know if I left out any pertinent information.

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dj3

· #2 · May 25, 2020

Your pictures may not tell the whole story about the condition and integrity of the concrete.
A slab for what you are thinking of doing must meet certain standards (prep work, footing, rebar, etc), so have professionals look at it and assess it..
If it were me - break it away and start fresh.

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de-nagorg

· #3 · May 25, 2020

You are trying to make a gold nugget from a turd.

It will cost more to "band-aid" the existing mess, and keep having problems with it forever.

My advice is to Pay now to have it removed, and start from the base gravel, up.

ED

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MittensCat

Discussion Starter · #4 · May 25, 2020

Thanks for the advice. I'd love to start new, just not sure I can afford it. I removed about 50 feet of sidewalk with a 16lb sledge and spud bar. I learned that concrete is heavier that I thought and moving it by hand is not fun. I ended up weighing every chunk on a bathroom scale so that I wouldn't overload the dumpster. I ended up with 7,000lbs in what they said was a 5 ton max. They wouldn't deliver a roll off to my street. The truck could barely lift the dumpster and there's no way they were picking up 5 tons. I think the driver was a little concerned about the drive back. I can only guess this slab and whatever is underneath is probably over 10 tons.

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MittensCat

Discussion Starter · #5 · May 25, 2020

Another vote for removal and start new I see. Turd to gold... nice one.

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stadry

· #6 · May 25, 2020

would make sense to me HOWEVER its yours & i can't really judge the existing conc's condition,,, if farm tractor & **** spreader parking spot, great,,, future man cave ? not so great.
pole size & depth of pole depends on uplift wind load, dimensions of bldg, etc,,, you won't be using the existing conc for anything but a place to park or walk on,,, pole barns are self-supporting therefore do not require floors

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de-nagorg

· #7 · May 25, 2020

stadry said:
would make sense to me HOWEVER its yours & i can't really judge the existing conc's condition,,, if farm tractor & **** spreader parking spot, great,,, future man cave ? not so great.
pole size & depth of pole depends on uplift wind load, dimensions of bldg, etc,,, you won't be using the existing conc for anything but a place to park or walk on,,, pole barns are self-supporting therefore do not require floors

Surely you meant a concrete floor, All pole barns start with a DIRT floor, things don't float, although that would be a fascinating sight.:devil3:

My neighbor had a pole barn built, with a dirt floor, but soon he had a full concrete floor poured inside, due to the dust, and messy factor.

ED

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chandler48

· #8 · May 25, 2020

One more vote for R&R. You indicated the top slab was poured around the studs. Even if you were able to pull the studs, you still have the rotting plates on bottom, under the second pour.

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MittensCat

Discussion Starter · #9 · May 25, 2020

The rotted plates are long gone, but the void remains and it makes for an unstable foundation. The issue here is that this neighborhood doesn't deserve a nice garage. Haha! With every shooting, dope fiend parked out front, and bag of trash dumped from a moving car, the value of my house is diminished. I think you understand what I'm describing 😉. So its a matter of slapping lipstick on a pig. Ill never recoup a $20k garage and I'm not planning on fighting the disintegration of the this city any longer. My other option is remove it and turn it to lawn, but I think a parking or storage space would help me sell.

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ChuckTin

· #10 · May 25, 2020

I feel your pain. Once a area starts going down its almost impossible to stop.
Have you considered forming around the existing concrete, with 2x12s and pouring a leveling slab on top? You might entomb the old stuff enough to stabilize all by using fiber reinforce additive in the mix.

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Nealtw

· #11 · May 25, 2020

MittensCat said:
The rotted plates are long gone, but the void remains and it makes for an unstable foundation. The issue here is that this neighborhood doesn't deserve a nice garage. Haha! With every shooting, dope fiend parked out front, and bag of trash dumped from a moving car, the value of my house is diminished. I think you understand what I'm describing 😉. So its a matter of slapping lipstick on a pig. Ill never recoup a $20k garage and I'm not planning on fighting the disintegration of the this city any longer. My other option is remove it and turn it to lawn, but I think a parking or storage space would help me sell.

Your pole barn would likely be the cheapest way of doing it.

The slab could be replaced any time after that if needed.

Water can be a problem if the slab sticks out past the walls and you may not want the walls touching the slab in case it moves a little.

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House Designer

· #12 · May 25, 2020

Can't really tell whether it is a detached garage from your pics. If detached, could you build a 27' x 20' pole structure just beyond the slab, then fill in any gaps with concrete later? No concrete cutting or moving involved.