Question:
Under Florida Law there is no case where a railing could be subject to the requirements of both codes. The residential code applies only to one and two-family dwellings. Florida Statute specifically exempts one and two-family dwellings from the Florida Fire Prevention Code, including NFPA 101, Florida Edition.

Most people who don't know the code wuss out, waste their clients money, and build at 42". It's why architects have such a poor reputation in the residential market.

Answer: I followed up with NFPA on Friday and learned that Florida exempted Single Family from the fire codes. Personally, I'm surprised, as I feel more comfortable standing at a 42" high rail than 36".

As to your second comment, I am continually trying to reach a level of perfection in my professional life which includes memorization of every code and all changes no matter how small. But I am comforted in knowing that until I get there, I have those wiser than me to remind me of my imperfections. As to the cost increases my clients have paid to my lack of knowledge, I appologize, but future clients who want 36" high rails will have to sign a hold harmless release stating that they acknowledge 36" is only a minimum code requirement and that according to my belief, knowledge and professional judgement this should be 42".