Pls help me floodproof our building lobby

dnereidSeptember 4, 2011

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.


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Unfortunately there is no way to "floodproof" wood building construction that I know of. Unless you can seal off every possible entry point of water from the exterior, "water will always find a way".

    Bookmark   September 4, 2011 at 3:42AM
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First of all, on top of the plywood, you only need cement board OR Ditra. They are both underlayments. If you use Ditra (I much prefer it, as it's way easier and faster to lay), and tape the seams, it will waterproof the floor.


That's waterproofing from someone spilling on the floor, not from a flood that rises from below or an overwhelming flow of water that sweeps in from the outside. Waterproofing in bathrooms is done to keep water from getting into the walls from the inside the room. A flood does the opposite. I'm afraid floorman's right: you can't flood proof a building unless you build a dike around it.

    Bookmark   September 8, 2011 at 2:16PM
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You need to have licensed and insured contractors doing any work on your building. No homeowner DIY allowed on multi-family dwellings. You don't have the insurance to cover yourself if anything you do is wrong, and neither does your building.

    Bookmark   September 8, 2011 at 5:40PM
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You can't control flooding. If it's gonna's just gonna happen. You might consider having one or two linear drains installed, with an adequate slope to one or both, at least the water wouldn't just sit there for days.

    Bookmark   September 11, 2011 at 12:42PM
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