Got it @Ryan Judy, you're running into local building code of course which can be more restrictive than the state.If the lot has the square footage, could you build a second structure on the lot?

Property in question is a 20 tenant office building--I will get back to you with exact sq footage.

Or you can find homes that are not directly comparable in square footage, number of bedrooms, garage, other features and make adjustments for those.If you know another local investor or realtor you can ask them how they would go about finding comps in that area.

I just recently closed on a home there and looking for help adding square footage to the home.

Tell them they can access your camera footage for anything and they'll also likely give you info.

@Brook Bolger, to add to what Peter said, if/when your property is listed for sale, agents inevitably will ask why there is a discrepancy between public records stating your house has 3 bedrooms and also the square footage so you'll need to tell them that it takes some time for public records to be updated.For the STR portion, when you apply for your permit and state that it's a 4 bedroom (or 5 or whatever including the ADU's bedroom count if including the ADU for guest use), the county may ask you the same question and you'll need to supply the permits and certificate of occupancy.

I normally run numbers on storage units using the "industrial" settings as it can just all be broken down to square footages. 

Often times you will be fighting to justify the square footage of both the front and the ADU unit combined comp with SFH of that size.

@Enis ShehuWhat are you looking at for square footage in each condo?

Depending on the sq. footage/# of rooms your best bet may be a Ductless Split System.