Pls help me floodproof our building lobby
Our building was badly hit by Hurricane Irene. Our town is 4-5 feet below sea level.
Our wall to wall carpeted lobby, which had padding and plywood subfloor underneath, stood submerged for over 24 hours. We've thrown the carpet out and plywood is now warped.
My neighbor drilled a small hole in the plywood and it seems there is ground/dirt about 2-3 feet below (there are 2 steps leading into the building lobby). It is wet, but water is no longer stagnant after a week.
As condo owners, we know little about floors so I need some help from experts.
Will replacing the plywood subfloor, then cementboard, then ditra, then porcelain tile make this waterproof in case there is water logging for 24 hours? We are also planning on cutting out wet drywall (about 6") and replacing with cementboard (vertically). Should we put some sort of liner or vapor barrier at the seams? Would water ever rise up from below and is there a solution for that? The space is over 600 sqft so there is room to build a pitch.
Finally, do we need an engineer to inspect or suggest any drains etc. Or will a licensed general contractor do?
Any help would be appreciated.
Thank you very much.