Double pour slab foundation

I have not run across this before, approx. 80 % of exterior foundation has horizontal crack then in the garage i see that a secondary pour was made. I was able to see one small section that rebar was used to tie the separate pours tied together. What are your thoughts?

The lower floor elevation in the garage is to prevent spills in the garage from entering the basement or living space. Liquid spills such as gasoline would be contained in the garage space.

It is not unusual to have a stem wall on a built up slab. Pour the stem wall, fill-it, then poor the slab on top. What is unusual is the “Double foundation” in the garage.

I am not seeing a problem.


Agree with Brian.

Agree with your statement Brian, Not usual in my area at all. I am thinking foundation contractor screwed up on elevation on the perimeter thus the cracking along the outer wall

Building codes used to stipulate that the floor of an attached garage be four inches lower than the floor level of the house . The rationale for requiring this little step was that it would prevent spilled gasoline, gasoline vapors, and carbon monoxide from getting inside the house.


That had to be after they built my house. Mine is flush and was built in 67’ LOL

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Possibly, in my experience 99% of the time the parge coat cracks right along between the slab and the stem wall.


built in 1998

Stem wall  slab foundation

This is what i would typically see


Instead of using a header block, the garage slab would be boxed and poured on top. This usually gives you a 4" drop out of the structure, the outside would be stucco applied. Most of the time the stucco cracks due to the foundation wall and the slab being poured at different times so they are not bonded. No structural problems.

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And this is what we typically see :smiley:
(stem wall is often CMU block but is sometimes poured)

I’m thinking ADA got involved because I often see garage floors completely flush with interior floors (hopefully, the garage slab slopes away from the house). The whole vapor/liquid/CO thing is interesting. I’ve been programmed that 18" was necessary (water heaters were elevated this far in my area for years before being built to sit on the ground). Liquids? I can see the case for this - in my area snow melting and dropping from cars is one reason. CO? I dunno - we allow CO detectors on the ceilings so can’t imagine it settling and collecting within 4" of the floor is killing many people but anything is possible.

That 4" difference has some common sense to it, but that is not a building code around here. Gasoline vapor particularly when cold, will definitely pool on the ground. CO is only slightly heavier than air and will not pool in a typical environment. Even slight convection circulation will distribute it throughout the volume of a room.