I ran across this in an inspection yesterday. I was crawling around in the crawl and in the far corner I see a HVAC supply trunk running through the block foundation to the “new” addition that was built 15 yrs ago. After further examination, it appears that they dug a tunnel underneath the existing slab roughly 3’ x 3’ x 10’ long to the new addition that was built beyond this tunnel. I could see the metal lathe of the slab.The whole slab part used to be part of an eat in kitchen area. That area was roughly 10’x12’ This was for a maintenance inspection. They had the house inspected before they bought it a year ago but always felt that the inspector didn’t do a thorough job. I believe that it’s a structural issue and should be differed to a SE. But it has also been that way for 15 years. Has anyone else run across underming of slabs such as this. I just want to see what other inspectors would say about this.