Flood requirements on home additions?

We live in unincorporated Harris county. I have noticed that the homes being built in our neighborhood since Harvey are being majorly elevated, I am assuming because the construction requirements changed post-Harvey. Does anyone know if home additions fall subject to the same elevation requirements?

I am looking into doing an addition on my in-laws house (it is in the Shaded zone x). It did not flood in Harvey, but it was a close scrape. Will the county let us add a room at the same level or would it need to be a split level situation? (The addition is for elderly family members, so if it is split level, we will have to consider other options since they can't do stairs).