Concrete Advice for Basement Garage

[Proud Highway]

I have a 24x24 garage in the basement of my home. Directly above it sits a 24x24 garage on the ground level which is on a suspended concrete slab.

 

[DougWil]

Did the basement garage slab have rebar in it and how much?

A floating slab undoweled is best since is free to move without creating stresses.
You don't have to have a thick, compacted gravel base over the footing. You can use 1" of dense foam, in conjunction with a well compacted base under the balance of the slab and REBAR, #4 at 18in each way.

 

[Proud Highway]

Did the basement garage slab have rebar in it and how much?

This I don't know.

A floating slab undoweled is best since is free to move without creating stresses.

Makes sense.

You don't have to have a thick, compacted gravel base over the footing. You can use 1" of dense foam, in conjunction with a well compacted base under the balance of the slab and REBAR, #4 at 18in each way.

This is good to know, my only concern is 1" of dense foam + 4" concrete = 5" of lost ceiling height.

What about this?

 

[DougWil]

Yep, you can do that.

I take it you must not have any frost depth requirements since you have such a shallow footing??

 

[Proud Highway]

Yep, you can do that.

I take it you must not have any frost depth requirements since you have such a shallow footing??

Frost line is 30". I'm guessing that basement footings don't need to be below the frost line if they are within a certain distance and contiguous to footings that are. Walkout basements are very common in the foothills/mountains. From my observations this is how other homes in my community are built.

Here's a photo of the footings. Walkout basement. We have a pop out in the rear and it looks as though the footings for that were sunk below the frost line. Concrete walls around the entire perimeter of basement BTW.

 

[Radix2]

If your test is showing a stable situation, I would just patch and cover. Assuing you can live with the current height.

After the cost and expense to remove and replace the floor, you will still risk settling unless the contractor is careful with the new work.

With those extensive footings, I am surprised they settled - is it possible that there is (or was) something going on - water, expansive clays, etc that could have caused the floor to rise vs the footings to settle?

Love the views !

 

[Radix2]

and many many many slabs are poured over a lip in the stem walls - the worry is the floor may crack due to it setting - you have a unusual sort of issue there.

 

[Proud Highway]

The crack borders the entire slab about 12" from the wall. The crack is actually quite minor and typical for basement slab except for one 10' section. I've taken a photo of it at its worst. The spackle patch hasn't cracked in 2 years.