Anyway to Avoid Flood Vents in Flood-Prone Area?

[therattler]

Architect and Owner are insisting on NO flood vents in foundation walls (stem walls). House is in AE zone. I have scoured ASCE 24, FEMA bulletins, is there any responsible way to do this? Cost is not a problem.

thanks in advance, the rattler

 

[MiketheEngineer]

Why would they NOT want this. They could easily "save" the building during a flood event.

No way around it that I know of. Or move to higher ground.

 

[tolchijb]

My understanding is that you would need to design the structure for the 100 year flood (or better) for differential water pressures including wave action, currents, and debris. The idea being that the structure is water tight without flood vents and therefore must be able to withstand the forces of the flood waters and any debris in the current. I cannot site specific codes, but I did have a conversation with someone at the USACE along this topic a few years back. I would try to talk with someone at the corp of engineers or FEMA regarding specific provisions (if they exist).

Good luck.

 

[cvg]

don't forget about floatation... This is the killer - it is very difficult to construct a watertight basement in a flood zone that does not float.

 

[JAE]

per cvg.....agree its difficult - unless you provide a VERY thick base mat.

 

[youngstructural]

Or base the house on deep piles. I've seen this done in New Zealand frequently to enable building on liquifiable grounds... Essentially, in an Earthquake, the earth turns to liquid and the foundations must be able to take this material change. I've seen 150x150mm concrete piles go 9 to 15m deep in some cases, with the piles often being at 2m on centre each way. Not cheap, but it works...

You did say price was no object, right?

I would also encourage you to consider a water-tight concrete admix, such as Crystal or Xypex.

Hope that helped,
Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[therattler]

Update from the Rattler:

I appreciate the prompt and thoughtful replies. Part of my confusion comes from this: I've estimated the hydrostatic loads, based on the BFE against the foundation walls. It seems to me the loads are fairly meager, meaning a reinforced masonry wall, with some shear-wall type walls behind it, could easily resist the forces. If this is true, the requirement for flood vents seems a bit excessive. I respect the technical bulletins from FEMA, so where am I going wrong?

thanks in advance

 

[cvg]

have you assumed fully saturated soil plus ponded water above grade?

have you included any impact from debris?

have you considered the anchoring required to keep it from floating?