Unusual crawlspace configuration around chimney base

I encountered this trench on two sides of the crawlspace floor around the chimney base. I’ve never seen this before; any thoughts on what it’s designed to do?

Morning, Steven.
Hope this post finds you well and in good spirts today.

Please, explain more.
1: Type and age of building.
2: Did the home undergo modifications or repairs recently? Looks like a new slab.
Request disclosure from the vender.

Suspect: Repoured concrete slab atop prior crawlspace concrete floor.
No adverse conditions observed the day of the inspection.

It looks poor planning, to me.

Nothing to worry about, IMHO.

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Yes. As Larry indicated, an afterthought.

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Just a thought - The concrete guys were ahead of the masons on the schedule and blocked out the opening, but never came back to infill the area.


Single family home, 2001 build.
No modifications from original build

It is common in my area to build the chimney base lower than the floor so that any rainwater coming down the flue will leach into the ground and not on top of the floor. And no, chimney caps are not common in my area.

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I think it is a built up slab. The foundation stem wall and the footing for the fireplace was poured first. Then they poured the slab. They could have poured the slab and filled in the “trench” or save on concrete.

That doesn’t explain the thickness of the slab, too many unknowns.


Very true.

As pictured I don’t see any reportable defects. I’d guess the guys laying the crawl space slab just didn’t want to interfere with the chimney or its (assumed) footing.