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Flood resistant materials below BFE

Jay

Jay

SAWHORSE
Joined
Apr 8, 2018
Messages
90
Location
NJ, USA
Hello all! I am working on a new residential project and our environmental consultant has determined that the principal building will be located completely within Coastal A zone, elevation 10'. One foot freeboard required which puts the DFE, as I understand it, at elevation 11'. Typically this would reference bottom of wood framing. Floor will be approx. 6 feet above existing grade. Client is looking for a means to lower the first floor (against my recommendation of course).

The way I read the code, and what I have seen done in my area, is some designers are using treated wood framing... treated SYP for sills and joists, rim boards, marine grade plywood and treated PSL framing for beams all which seem to be considered "flood resistant material". The floodplain manager agreed it is allowed but asked for "Engineer of Record" to sign off on it.

Just curious if anyone has experience doing it this way as a means to save some height by not having the bottom of wood framing at the DFE but the top of subfloor. Anything to look out for, other than the obvious?

Thanks
 
I am just seeing this and a bit disappointed that there was never a reply. This forum is based on sharing information for questions like this. I will respond later when I have time to put the facts together even though this is extremely old.
 
I'm interested in this topic too. Does anything below the DFE need to be engineered to withstand the floodwaters? Or a breakaway wall which really can't be done to a floor system.
 
It's been a while since I did work in flood plains, but I think you can't have any mechanical equipment, ductwork or electrical devices below flood elevation. You also can't have gypsum board walls or insulation in the walls. Everything below flood elevation has to be able to get soaked with no long-term deterioration.

I believe the FEMA Coastal COnstruction Manual has additional information on what materials can and can't be used below flood elevation.
 
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