17.78.050 Provisions for flood hazard reduction | San Luis Obispo Municipal Code

17.78.050 Provisions for flood hazard reduction.

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 floodwaters around and away from proposed structures.

a. Residential Construction. 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 Building Official to be properly elevated. Such certification and verification shall be provided to the floodplain administrator. All new construction or substantial improvements of residential structures shall have the lowest floor, including basement:

i. In AE, AH, A1-30 zones, elevated one foot above the base flood elevation.

ii. In an AO zone, elevated above the highest adjacent grade to a height one foot above the depth number specified in feet on the FIRM, or elevated at least three feet above the highest adjacent grade if no depth number is specified.

iii. In an A zone, without BFEs specified on the FIRM [unnumbered A zone], elevated one foot above the base flood elevation; as determined under Section 17.78.040(B)(3) (Review, Use, and Development of Other Base Flood Data).

iv. In an XB zone, above the base flood elevation.

b. Nonresidential Construction. All new construction or substantial improvements of nonresidential structures shall either be elevated to conform with subsection (A)(3) (Elevation and Floodproofing) of this section or:

i. Be floodproofed, together with attendant utility and sanitary facilities, below the elevation recommended under subsection (A)(3) (Elevation and Floodproofing) of this section, so that the structure is watertight with walls substantially impermeable to the passage of water;

ii. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy; and

iii. Be certified by a registered civil engineer or architect that the standards of subsection (A)(3) (Elevation and Floodproofing) of this section 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:

i. For nonengineered 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; provided, that they permit the automatic entry and exit of floodwater; and

(d) Buildings with more than one enclosed area must have openings on exterior walls for each area to allow floodwater to directly enter; or

ii. Be certified by a registered civil engineer or architect.

i. Manufactured homes located outside of manufactured home parks or subdivisions shall meet the elevation and floodproofing requirement in subsection (A)(3) (Elevation and Floodproofing) of this section.

ii. Manufactured homes placed within manufactured home parks or subdivisions shall meet the standards in subsection D (Standards for Manufactured Homes Within Manufactured Home Parks or Subdivisions) of this section. Additional guidance may be found in FEMA Technical Bulletins TB 1-93 and TB 7-93.

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 (A)(3) (Elevation and Floodproofing) of this section. Areas of the garage below the BFE must be constructed with flood-resistant materials. See subsection (A)(2) (Construction Materials and Methods) 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.

(a) Accessory structures used solely for parking (two-car detached garages or smaller) or limited storage (small, low-cost sheds), as defined in Section 17.158.016—F Definitions, under Floodplain Management Regulations, may be constructed such that its floor is below the base flood elevation (BFE), provided the structure is designed and constructed in compliance 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 subsection F (Floodways) of this section; and

(6) The accessory structure must be designed to allow for the automatic entry of floodwaters in compliance with subsection (A)(3) (Elevation and Floodproofing) of this section.

(b) Detached garages and accessory structures not meeting the above standards must be constructed in compliance with all applicable standards in subsection A (Standards of Construction) of this section.

1. All new and replacement water supply and sanitary sewage systems shall be designed to minimize or eliminate:

a. Infiltration of floodwaters into the systems; and

b. Discharge from the systems into floodwaters.

2. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.

1. All new subdivisions proposals and other proposed development, including proposals for manufactured home parks and subdivisions, greater than fifty lots or five 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:

i. Lowest floor elevation.

ii. Pad elevation.

iii. Lowest adjacent grade.

2. All subdivision proposals and other proposed development shall be consistent with the need to minimize flood damage.

3. 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.

4. All subdivisions and other proposed development shall provide adequate drainage to reduce exposure to flood hazards.

D. Standards for Manufactured Homes Within Manufactured Home Parks or Subdivisions. All manufactured homes in special flood hazard areas shall meet the anchoring standards in subsection (A)(1) (Anchoring) of this section, construction materials and methods requirements in subsection (A)(2) (Construction Materials and Methods) of this section, flood openings requirements in subsection (A)(3) (Elevation and Floodproofing) of this section, and garages and low-cost accessory structure standards in subsection (A)(3) (Elevation and Floodproofing) of this section. Manufactured homes located outside of manufactured home parks or subdivisions shall meet the elevation and floodproofing requirement in subsection (A)(3) of this section.

1. All manufactured homes that are placed or substantially improved on sites located: (a) in a new manufactured home park or subdivision; (b) in an expansion to an existing manufactured home park or subdivision; or (c) in an existing manufactured home park or subdivision on a site upon which a manufactured home has incurred “substantial damage” as the result of a flood shall within zones A1-30, AH, and AE on the community’s flood insurance rate map, shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated one foot 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 subsection (D)(1) of this section shall 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 least one foot 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 thirty-six 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 building official, to be properly elevated. Such certification and verification shall be provided to the floodplain administrator.

1. All recreational vehicles placed in zones A1-30, AH, and AE shall either:

a. Be on the site for fewer than one hundred eighty consecutive days; or

b. 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

c. Meet the permit requirements of Section 17.78.040(C) (Development Permit) and the elevation and anchoring requirements for manufactured homes in subsection (D)(1) of this section.

F. Floodways. Since floodways are extremely hazardous areas due to the velocity of floodwaters that 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 allowed 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 one foot at any point within the city.

2. If the proposed development is within a designated infill area, special floodplain management zone, or the Mid-Higuera Specific Plan Area as defined by the Drainage Design Manual, the more stringent requirements of the manual apply.

3. Within an adopted regulatory floodway, the city 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.

4. If subsections (F)(1) and (F)(2) of this section are satisfied, all new construction, substantial improvement, and other proposed new development shall comply with all other applicable flood hazard reduction provisions of this subsection. (Ord. 1650 § 3 (Exh. B), 2018)