"How do you raise an island? Does the former first floor of a house that survived the hurricane become it's basement?"
There weren't any houses on the island after that hurricane. They started over.
Not true. Plenty of the old victorians and even some antebellum houses survived, and you can tour many of them every year at the GHF Historic Home Tour (excuse the plug) Palladin I think said that they let the first floors of masonry bldgs become basements under the fill, but in fact they were jacked up too (Ashton Villa, Bishops Palace plus scores of others, including big old honkin' churches). Really an amazing feat.