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Re: [AEC-Residential] Beach House Foundation

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The original question from the seaint listserve was posted to
flood_haz_mit(--nospam--at)yahoogroups.com (formerly egroups). The following is a reply
which was received.

James Cohen
James Cohen Consulting, P.C.
PO Box 130
Pennington, NJ 08534
Tel: (609) 730-0510
Fax: (609) 730-0511
Website: http://u2.expertpages.com/jccpc

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Near-ocean buildings offer unique design problems because of the
likelihood of erosion under the building during severe individual storms
and the accumulation of long-term erosion during the lifetime of the
building.  Even in high sand dunes, erosion can allow storm waves threaten
the house.  Flooding damages a house but a single  wave larger than 1.5
feet will destroy it. Plan for erosion.  Avoid the waves hitting a solid
wall or plan to lose the house.
  The described style of construction has been common in coastal South
Carolina since the 1950s.  As a result several hundred similar beach houses
were destroyed in the fringes of Hurricane Hugo in 1989.
The potential for erosion near the ocean generally dictates a piling
foundation as the best and most cost effective solution.  Deep piling
foundations proved successful in Hurricane Fran. See the FEMA's Building
Performance Assessment Team report on Fran:

http://www.fema.gov/mit/bpat/bpat008.htm

The closer to the ocean the deeper the pilings need to extend below sea
level .  For more details get a CD copy of FEMA's new Coastal Construction
Manual:

www.fema.gov/mit/bpat/

If piling are not an option then the best solution is not to build the
house.  Grade beams and integral parking slabs with piers just add to the
wave loads and make it easier for erosion and waves to destroy the house.
It's best to isolate the slab from the foundation.

My best advice: If you have the bucks to buy beachfront, hire a shoreline
specialist in coastal engineering or geology to assess the erosion and
storm risk on your site, and to design the foundation accordingly.   While
you are at it, consider adding 3 or 4 feet of added floor elevation to the
FEMA minimums.  Each foot above the minimum lowers your annual flood
insurance premiums.

Spencer Rogers
NC Sea Grant