In all areas of special flood hazards the following standards are required:
A. Anchoring. All new construction and substantial improvements of structures, including manufactured homes, shall be adequately anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy.
B. Construction Materials and Methods. All new construction and substantial improvements of structures, including manufactured homes, shall be constructed:
1. With flood-resistant materials, and utility equipment resistant to flood damage for areas below the base flood elevation;
2. Using methods and practices that minimize flood damage;
3. With electrical, heating, ventilation, plumbing and air conditioning equipment and other service facilities that are designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding; and
4. Within zone AH or AO, so that there are adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.
C. Elevation and Floodproofing.
1. Residential Construction. All new construction or substantial improvements of residential structures shall have the lowest floor, including basement:
a. In AE, AH, and A1-30 zones, elevated two feet above the base flood elevation (78 feet).
b. In an AO zone, elevated above the highest adjacent grade to a height two feet above the depth number specified in feet on the FIRM (78 feet), or elevated at least four feet above the highest adjacent grade if no depth number is specified.
c. In an A zone, without BFEs specified on the FIRM (unnumbered A zone), elevated two feet above the base flood elevation; as determined under SMC 15.16.140(C).
Upon the completion of the structure, the elevation of the lowest floor, including basement, shall be certified by a registered civil engineer or licensed land surveyor, and verified by the community building inspector to be properly elevated. Such certification and verification shall be provided to the Floodplain Administrator.
2. Nonresidential Construction. All new construction or substantial improvements of nonresidential structures shall either be elevated to conform with subsection (C)(1) of this section; or:
a. Be floodproofed, together with attendant utility and sanitary facilities, below the elevation recommended under subsection (C)(1) of this section, so that the structure is watertight with walls substantially impermeable to the passage of water;
b. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy; and
c. Be certified by a registered civil engineer or architect that the standards of subsections (C)(2)(a) and (b) of this section are satisfied. Such certification shall be provided to the Floodplain Administrator.
3. Flood Openings. All new construction and substantial improvements of structures with fully enclosed areas below the lowest floor (excluding basements) that are usable solely for parking of vehicles, building access or storage, and which are subject to flooding, shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwater. Designs for meeting this requirement must meet the following minimum criteria:
a. For nonengineered openings:
i. Have a minimum of two openings on different sides having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding;
ii. The bottom of all openings shall be no higher than one foot above grade;
iii. Openings may be equipped with screens, louvers, valves or other coverings or devices provided that they permit the automatic entry and exit of floodwater; and
iv. Buildings with more than one enclosed area must have openings on exterior walls for each area to allow floodwater to directly enter; or
b. Be certified by a registered civil engineer or architect.
4. Manufactured Homes.
a. See SMC 15.16.200.
b. Garages and Low-Cost Accessory Structures.
i. Attached Garages.
(A) A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry of floodwaters. See subsection (C)(3) of this section. Areas of the garage below the BFE must be constructed with flood-resistant materials. See subsection B of this section.
(B) A garage attached to a nonresidential structure must meet the above requirements or be dry floodproofed. For guidance on below grade parking areas, see FEMA Technical Bulletin TB-6.
ii. Detached Garages and Accessory Structures.
(A) “Accessory structures” used solely for parking (two-car detached garages or smaller) or limited storage (small, low-cost sheds), as defined in SMC 15.16.050, may be constructed such that its floor is below the base flood elevation (BFE), provided the structure is designed and constructed in accordance with the following requirements:
(1) Use of the accessory structure must be limited to parking or limited storage;
(2) The portions of the accessory structure located below the BFE must be built using flood-resistant materials;
(3) The accessory structure must be adequately anchored to prevent flotation, collapse and lateral movement;
(4) Any mechanical and utility equipment in the accessory structure must be elevated or floodproofed to or above the BFE;
(5) The accessory structure must comply with floodplain encroachment provisions in SMC 15.16.220; and
(6) The accessory structure must be designed to allow for the automatic entry of floodwaters in accordance with subsection (C)(3) of this section.
(B) Detached garages and accessory structures not meeting the above standards must be constructed in accordance with all applicable standards in this article.
c. Crawl Space Construction. This subsection applies to buildings with crawl spaces up to two feet below grade. Below-grade crawl space construction in accordance with the requirements listed below will not be considered basements.
i. The building must be designed and adequately anchored to resist flotation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. Crawl space construction is not allowed in areas with flood velocities greater than five feet per second unless the design is reviewed by a qualified design professional, such as a registered architect or professional engineer;
ii. The crawl space is an enclosed area below the BFE and, as such, must have openings that equalize hydrostatic pressures by allowing for the automatic entry and exit of floodwaters. For guidance on flood openings, see FEMA Technical Bulletin 1-93;
iii. Crawl space construction is not permitted in V zones. Open pile or column foundations that withstand storm surge and wave forces are required in V zones;
iv. Portions of the building below the BFE must be constructed with materials resistant to flood damage. This includes not only the foundation walls of the crawl space used to elevate the building, but also any joists, insulation, or other materials that extend below the BFE; and
v. Any building utility systems within the crawl space must be elevated above BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions.
vi. Requirements for all below-grade crawl space construction, in addition to the above requirements, to include the following:
(A) The interior grade of a crawl space below the BFE must not be more than two feet below the lowest adjacent exterior grade (LAG), shown as D in Figure 3 of Technical Bulletin 11-01;
(B) The height of the below-grade crawl space, measured from the interior grade of the crawl space to the top of the crawl space foundation wall must not exceed four feet (shown as L in Figure 3 of Technical Bulletin 11-01) at any point;
(C) There must be an adequate drainage system that removes floodwaters from the interior area of the crawl space within a reasonable period of time after a flood event, not to exceed 72 hours; and
(D) The velocity of floodwaters at the site should not exceed five feet per second for any crawl space. For velocities in excess of five feet per second, other foundation types should be used. (Ord. 1084, 2016)