Renovating a duplex that is listed as SF on county records

[Marsha Rost]

I have found a good deal on a house that was built in 1910. It was a single family home that was turned into a duplex and the conversion must have happened a long time ago. However it is still catagorized as single family on county records.

It needs a complete top to bottom rehab. I would like to keep it as a duplex. I wanted to know, since it's not legally a duplex, what will the city require us to do when applying for permits. For example, are they going to make us create a fire rated separation wall. What do I need to do to have it legally listed as multi family?

The property is in Houston TX.

Thank you all in advance