Zoning codes vary by area so I would check the local zoonning codes and call the permitting office to see if it has a use and occupnacy permit for a SFH. 

I am looking at 2 properties in particular. 1 has taxes of $28K and 1 is $13K and both are in the same zip code both 4 units.

It's the largest city by land mass in the US, so there are great pockets that many people miss on because they only look at zip codes.

Which portion of the tax code do they reference / how are they interpreting it?

You have code enforcement issue in one of those cities and they do not know you, your life is not going to be easy meanwhile the person who has been there for 10 years and knows the inspectors families name will have a very different outcome than yours. 

I have extensive knowledge of working with Pinellas county and the city to get your Airbnb in good standing with their codes and requirements, along with access to many tools and systems to generate free analyses for you on any property.

If you are using battery powered you have to change codes often (one code for showing - should be deleted after showing season, one code for tenant that needs to be changed after each tenant) and you need to replace the batteries every time it goes vacant so that you don't end up with a tenant dead battery and a tenant locked out.

Another reason why engaging an architect early is helpful is to ensure the layouts are permitted from the perspective of code requirements.

We're a partner of theirs and have code BNBCALC for $50 off.

She worked for the code enforcement.