A. Standards of construction. In all areas of special flood hazards the following standards are required:
1. 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.
2. Construction materials and methods. All new construction and substantial improvements of structures, including manufactured homes, shall be constructed:
a. With flood resistant materials, and utility equipment resistant to flood damage for areas below the base flood elevation;
b. Using methods and practices that minimize flood damage;
c. 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
d. Within Zones AH or AO, so that there are adequate drainage paths around structures on slopes to guide flood waters around and away from proposed structures.
3. Elevation and floodproofing.
a. Residential construction. All new construction or substantial improvements of residential structures shall have the lowest floor, including basement:
(1) In AE, AH, A1-30 Zones, elevated to or above the base flood elevation.
(2) In an AO zone, elevated above the highest adjacent grade to a height equal to or exceeding the depth number specified in feet on the FIRM, or elevated at least 2 feet above the highest adjacent grade if no depth number is specified.
(3) In an A zone, without BFE’s specified on the FIRM [unnumbered A zone], elevated to or above the base flood elevation; as determined under Section 15.08.070.B.3.
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.
b. Nonresidential construction. All new construction or substantial improvements of nonresidential structures shall either be elevated to conform with Section 15.08.080.A.3.a or:
(1) Be floodproofed, together with attendant utility and sanitary facilities, below the elevation recommended under Section 15.08.080.A.3.a, so that the structure is watertight with walls substantially impermeable to the passage of water;
(2) Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy; and
(3) Be certified by a registered civil engineer or architect that the standards of Section 15.08.080.A.3.b(1) and (2) are satisfied. Such certification shall be provided to the Floodplain Administrator.
c. 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:
(1) For non-engineered openings:
(a) 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;
(b) The bottom of all openings shall be no higher than one foot above grade;
(c) Openings may be equipped with screens, louvers, valves or other coverings or devices ;
(d) Buildings with more than one enclosed area must have openings on exterior walls for each area to allow flood water to directly enter; or
(2) Be certified by a registered civil engineer or architect.
d. Manufactured homes. See Section 15.08.080.D.
e. Garages and low cost accessory structures.
(1) 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 flood waters. See Section 15.08.080.A.3.c. Areas of the garage below the BFE must be constructed with flood resistant materials. See Section 15.08.080.A.2.
(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.
(2) Detached garages and accessory structures. “Accessory structures” used solely for parking (2 car detached garages or smaller) or limited storage (small, low-cost sheds), as defined in Section 15.08.050, 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:
(a) Use of the accessory structure must be limited to parking or limited storage;
(b) The portions of the accessory structure located below the BFE must be built using flood-resistant materials;
(c) The accessory structure must be adequately anchored to prevent flotation, collapse and lateral movement;
(d) Any mechanical and utility equipment in the accessory structure must be elevated or floodproofed to or above the BFE;
(e) The accessory structure must comply with floodplain encroachment provisions in Section 15.08.080.F; and
(f) The accessory structure must be designed to allow for the automatic entry of flood waters in accordance with Section 15.08.080.A.3.c.
(3) Detached garages and accessory structures not meeting the above standards must be constructed in accordance with all applicable standards in Section 15.08.080.A.
B. Standards for utilities.
1. All new and replacement water supply and sanitary sewage systems shall be designed to minimize or eliminate:
a. Infiltration of flood waters into the systems; and
b. Discharge from the systems into flood waters.
2. On site waste disposal systems shall be located to avoid impairment to them, or contamination from them during flooding.
C. Standards for subdivision and other proposed development.
1. All new subdivisions proposals and other proposed development, including proposals for manufactured home parks and subdivisions, greater than 50 lots or 5 acres, whichever is the lesser, shall:
a. Identify the Special Flood Hazard Areas (SFHA) and Base Flood Elevations (BFE).
b. Identify the elevations of lowest floors of all proposed structures and pads on the final plans.
c. If the site is filled above the base flood elevation, the following as-built information for each structure shall be certified by a registered civil engineer or licensed land surveyor and provided as part of an application for a Letter of Map Revision based on Fill (LOMR-F) to the Floodplain Administrator:
(1) Lowest floor elevation.
(2) Pad elevation.
(3) Lowest adjacent grade.
2. All subdivision proposals and other proposed development shall be consistent with the need to minimize flood damage.
a. All subdivision proposals and other proposed development shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.
b. All subdivisions and other proposed development shall provide adequate drainage to reduce exposure to flood hazards.
D. Standards for manufactured homes.
1. All manufactured homes that are placed or substantially improved, on sites located: (1) outside of a manufactured home park or subdivision; (2) in a new manufactured home park or subdivision; (3) in an expansion to an existing manufactured home park or subdivision; or (4) in an existing manufactured home park or subdivision upon which a manufactured home has incurred “substantial damage” as the result of a flood, shall:
a. Within Zones A1 30, AH, and AE on the community’s Flood Insurance Rate Map, be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated to or above the base flood elevation and be securely fastened to an adequately anchored foundation system to resist flotation, collapse, and lateral movement.
2. All manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision within Zones A1 30, AH, and AE on the community’s Flood Insurance Rate Map that are not subject to the provisions of Section 15.08.080.D.1 will be securely fastened to an adequately anchored foundation system to resist flotation, collapse, and lateral movement, and be elevated so that either the:
a. Lowest floor of the manufactured home is at or above the base flood elevation; or
b. Manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than 36 inches in height above grade.
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.
E. Standards for recreational vehicles. All recreational vehicles placed in Zones A1-30, AH, and AE will either:
1. Be on the site for fewer than 180 consecutive days; or
2. Be fully licensed and ready for highway use. A recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and security devices, and has no permanently attached additions; or
F. Floodways. Since floodways are an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and erosion potential, the following provisions apply:
1. Until a regulatory floodway is adopted, no new construction, substantial development, or other development (including fill) shall be permitted within Zones A1-30 and AE, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other development, will not increase the water surface elevation of the base flood more than 1 foot at any point within the City of Gridley.
2. Within an adopted regulatory floodway, the City of Gridley shall prohibit encroachments, including fill, new construction, substantial improvements, and other development, unless certification by a registered civil engineer is provided demonstrating that the proposed encroachment shall not result in any increase in flood levels during the occurrence of the base flood discharge.