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Question DetailsAsked on 12/20/2017

Fema requirements 1 foot BFE, Is it possible to raise a house with the basement? instead of filling the basement.

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Maybe remotely possible, but I have never heard of it being done, and I would expect it to cost about or more than the value of the house.

One thing I have done - though depends on the FEMA agreement your city or county operates under, is converting the basement into a crawlspace, with adequate authorized "engineered openings" to ensure it floods rapidly in a flood event which could otherwise collapse the walls with the water pressure. Sometimes this means holes or pipes through thge foundation walls, or if a structural/civil engineer stipulates on the certification that the foundation can handle full exterior submergence (both structurally and waterproofing wise), then adequate openings such that it will fill up if the foundation is overtopped. Then the house can be jacked up, the foundation walls extended up to the BFE +1 in your case, and the house set back on top of it.

It is possible to retain the basement as such but requires a detailed structural and waterproofing design and report by an engineer - normally not done for existing house because the retrofit costs too much to give it a truly waterproof basement, though of course buildings like highrises near rivers or coastlines routinely have their new (original) foundations designed this - like the 7 levels of sub-basement in the World Trade Center buildings which I worked on the design of. (Oops - I have dated myself).

Generally, going to be cheaper to convert the basement to a crawlspace by FEMA definitions, and raise the house and put in new supports for the house (assuming just a foot or two) on top of the existing foundation walls, assuming they can carry the extra height OK (which most concrete and block walls would, ,brick and stone maybe not). Of course, if talking a large raising needed, then putting it on beams and driven steel piles is the normal solution, with new stairs down to the ground level - or sometimes over-raising it temporarily and then filling in underneath with compacted structural fill and new strip foundations to the required level, then lowering it onto the new foundation.

Another rarely used solution, again requiring a formal design and report by an engineer so not cheap, is to design and build a waterproof berm all around the house to act as a levee - though normally this is not feasible as the native soils in flood-prone areas are too pervious so the wate would go under the levee and pop up inside. Normally only used for structures of high or historic value that spending a lot of money on preserving them is worth it, or where tearing it down or letting it flood is unacceptable. Another issue is you have to have foolproof backup generators and fuel storage to run pumps to dewater the "bathtub" that creates, which most residential projects cannot afford or provide.

An Architect or Civil Engineering firm specializing in FEMA compliance would be the people to talk to about your options in your specific situation.

Answered 2 years ago by LCD

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