Garage Cracks & Home Structure

We’ve all seen it - large cracks running through a garage floor. My understanding is that aside from situations such as a basement underneath a garage, typically the garage floor is a separately poured slab from the home foundation, and cracking in a garage floor, even significant ones, are not indicators of anything affecting the foundation / structure of the home itself.

Is this understanding correct? I’m wondering if garage floors are ever poured with the foundation. I came across some more notable cracking in a floor this week in a slab-on-grade construction, and since the vast majority of the foundation is not visible, I question whether cracking can indicate a general soil issue for the home.

You are correct in in saying the garage slab is always poured separately from the foundation walls.

Well, sometimes a monolithic slab is poured:

Thanks to:

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Post pics, if it’s not a shrinkage crack and there is displacement, it could indicate improper compacting, not using virgin soil, soil movement, etc…

Good point. Are there any indicators of whether or not it is a single pour?

You will typically see a seam around the perimeter if it’s not monolithic.

Simon is right… :smile:

Not many good pics, as the garage was packed full of stuff. It’s only about 2 mm wide and runs from the middle of the driveway to the back of the garage, and before it hits the curb it runs right all the way to the other side of the garage. Looks like a large “L”.

Gotcha. I am used to seeing a clearly defined seam near the edge and it looks like this might be a single pour :thinking:

I’ve not seen it poured like that:

op is mono-slab from my view here
cracks can be from improper soil compaction or heave
curb chip appears to be impact damage
below is typical mono-slab from around here


In addition to a seam you’ll often see expansion joint material separating the garage floor slab from the foundation walls/curb.

Depends on what area you are in. Both types of floor are common. In northern areas the floor is commonly poured separately. In southern climates the monolithic pour is used more often. Soil types and average temperature are determining factors.