Why would there be an 8in gap under slab?
I’m guessing this may be bad news or there is a reason. There was a hole in basement slab by furnace. I noticed couldn’t see or feel solid ground with my finger. So I fit a tape measure in and there is 8in gap from top of slab to what feels like solid ground. Why would that be? If so would I technically have less work to pour a new slab. I mean that is plenty of room to put in insulation poly and new 4 inch pad. I have repaired a different part of floor years back when there was a damaged piece of concrete and it was dirt right under thin layer of slab. If pouring a new slab is necessary this would force me to do so. Is this gap because of water lines running under floor?
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