Probably one of top three reasons for mold in an attic or underside of roof decking...

Most mobile homes don’t sit on a foundation, so a vapor barrier is affixed to the underside of the home, keeping out moisture home.

The home has been occupied by tenants for the last several years.I would plan to have the underside of the roof painted in the attic to cover up the black coloring.

Just because you see a shiny quarter on the ground --and go to pick it up--doesn't mean there's not a gross goober stuck to the underside. 

Additionally, 14B-2-202 Defines a Basement as:“Basement: A story that is not a story above grade plane.”Additionally, 14B-6-605 notes:“Except in buildings of group R-5 occupancy, floor construction over basements shall have afire-resistance rating of not less than 1 hour.”This means that if you are Very close to missing the 7'-0" mark, you can leave the ceiling unfinished and measure from the floor finish (a thin LVT or Vinyl tile would be recommended) and the Underside of the Joist.Note: Rooms containing gas-fired appliances (i.e.

This is taken from the height of the existing grade in the front yard to the underside of the first-floor joist. 

Or in you case, where its only on the first floor, you will have to rate to the underside of the floor decking above AND fire rate the ceiling as well (if there is livable space above that is not associated with this ADU/STR).

@Amiris Brown Yes chalk that one up to learning, there are always deals out there and the more numbers you crunch the better you'll get at your estimates.Regarding the mold, I've never heard of anyone removing and sanding the undersides of the hardwood, but that's not to say its not done.

I walk the pool if there is one on the property to see what the plaster/pebbletec looks like and the underside of the lip.  

Look at those plumbs :-)  My bathroom from the underside.