In addition to the requirements of ASCE 24, all post-FIRM new buildings and substantial improvements in a Coastal A-Zone shall comply with the V-Zone construction standards of Section G304.2.
Exceptions: The following structural systems shall be permitted in a Coastal A-Zone:
- Wave-resisting stem wall foundation. Stem walls supporting a floor system above, and backfilled with soil or gravel to the underside of the floor system, shall be permitted in Coastal A-Zones. The design and construction of the shallow foundation system shall comply with the following:
- The underside of such floor system shall be located at or above the design flood elevation specified in ASCE 24, Table 4-1.
- Stem walls enclosing areas below the design flood elevation shall not be permitted. Stem walls shall be designed to transfer all vertical and lateral forces to the slab above and to the foundation elements below;
- The design shall consider all forces resulting from flooding, including wave action, debris impact, erosion, and local scour;
- The design shall consider all forces resulting from soil pressure behind the walls, including the effect of hydrostatic loads, and all live and dead surcharge loads from the slab above;
- Flood openings shall not be required in stem walls constructed in accordance with this section;
- Where soils are susceptible to erosion and local scour, stem walls shall be supported by deep footings;
- Shallow foundations including spread footing, mat and raft foundations shall be designed to prevent sliding, uplift, or overturning when exposed to the combination of loads in ASCE Section 1.6.2.
- Wave-resisting dry floodproofing wall and foundation system. Buildings that are non-residential (for flood zone purposes) and that are located in Coastal A-Zones shall be permitted to be dry floodproofed in accordance with Section G304.1.2 provided the structure is dry floodproofed to at or above the design flood elevation specified in ASCE 24, Table 6-1. For buildings or structures utilizing this exception, construction documents shall include calculations demonstrating that the foundation and building, including flood shields if provided, will resist the wave action, including the combination of loads in ASCE Section 1.6, to at or above the design flood elevation specified in ASCE 24, Table 4-1.