G304.3 Coastal A-Zone construction standards.

In addition to the requirements of ASCE 24, all post-FIRM new buildings, horizontal enlargements and substantial improvements in a Coastal A-Zone shall comply with the coastal high-hazard area construction standards of Section G304.2.

   Exceptions: The following structural systems shall be permitted in a Coastal A-Zone:

      1.   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:

         1.1.   The underside of such floor system shall be located at or above the design flood elevation specified in ASCE 24, Table 4-1.

         1.2.   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;

         1.3.   The design shall consider all forces resulting from flooding, including wave action, debris impact, erosion, and local scour;

         1.4.   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;

         1.5.   Flood openings shall not be required in stem walls constructed in accordance with this section;

         1.6.   Where soils are susceptible to erosion and local scour, stem walls shall be supported by deep footings;

         1.7.   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 24, Section 1.6.2.

      2.   Wave-resisting dry floodproofing wall and foundation system. Buildings that are nonresidential (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. Such structure shall be dry floodproofed to or above the design flood elevation specified in ASCE 24, Table 6-1. Flood zone compliance plans 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 24, Section 1.6, to or above the design flood elevation.

(Am. L.L. 2023/077, 6/11/2023, eff. 6/11/2023)

Editor's note: For related unconsolidated provisions, see Appendix A at L.L. 2023/077.

G304.4 Construction standards for shaded X-Zones.

In shaded X-Zones, flood design class 4 buildings, as defined in ASCE 24, Table 1-1, shall comply with the requirements of this appendix and the applicable provisions of ASCE 24 for A-Zone construction.

G304.4.1 Alterations to certain flood design class 4 buildings.

Where existing emergency vehicle garages and fire, rescue, ambulance, and police stations located within shaded X-Zones are undergoing either a substantial improvement or an increase in the degree of noncompliance as such term is described in Item 10 of Section G102.1, they shall comply with this appendix to the maximum extent practicable as described in Sections G304.4.1.1 through G304.4.1.4.

G304.4.1.1 Existing emergency vehicle garages and fire, rescue, ambulance, and police stations to remain.

Where an existing emergency vehicle garage or fire, rescue, ambulance, or police station building is undergoing substantial improvement or an increase in the degree of noncompliance, such existing emergency vehicle storage area shall be permitted to be located below the design flood elevation, provided such space is wet floodproofed in accordance with ASCE 24 and an emergency action plan is filed with the department in accordance with ASCE 24, Section 6.2.3. Such emergency action plan shall include actionable directives for the relocation of such emergency vehicles in advance of a flood event.

G304.4.1.2 Equipment within existing emergency vehicle garages and fire, rescue, ambulance, and police stations.

Where an existing emergency vehicle garage or fire, rescue, ambulance, or police station building is undergoing substantial improvement or an increase in the degree of noncompliance, equipment necessary to support operations of such facilities may be located below the design flood elevation where elevation of such equipment to the design flood elevation is physically unfeasible. Such equipment shall be elevated to the maximum extent practicable.