This is what the ICC codes are missing: (it's from the old South Florida Building Code - Broward County Edition)
- 105 Maintenance Of Buildings And Property
- - 105.1 Buildings:
- - - (a) The requirements contained in this Code, covering the maintenance of buildings, shall apply to all buildings and/or structures now existing or hereafter erected. All buildings and/or structures and all parts thereof shall be maintained in a safe condition, and all devices or safeguards which are required by this Code shall be maintained in good working order.
- - - (b) This Sub-section shall not be construed as permitting the removal or non-maintenance of any existing devices or safeguards unless authorized by the Building Official and/or Chief Fire Official.
With that, the city would have won hands down.
This is from the 2006 IRC:
- R102.7 Existing structures.
The legal occupancy of any structure existing on the date of adoption of this code shall be permitted to continue without change, except as is specifically covered in this code, the International Property Maintenance Code or the International Fire Code, or as is deemed necessary by the building official for the general safety and welfare of the occupants and the public.
This is less forward and offers less back up for the city, it really hinges on the parts I have underlined above.
"legal occupancy"
"existing on the date of adoption of this code"
"except as is specifically ... or as deemed necessary by the building official"
If that occupancy was not "legal", i.e., it was made into a multi-family without permits, etc., then it was not "existing on the date of the adoption of this code", and, regardless, "except as ... deemed necessary by the building official", then the city 'has the right' to demand changes.
If the facts support it (and we only have a few of the facts), the city could 'deem the structure an unsafe structure' and that would certainly throw a wrench into the ballgame.