15.18.050 Provisions for Flood Hazard Reduction

15.18.050 Provisions for Flood Hazard Reduction.

A. Standards of Construction. In all areas of special flood hazards the following standards are required:

a. All new construction and substantial improvements 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. All manufactured homes shall meet the anchoring standards of subsection (D) of this section.

2. Construction Materials and Methods. All new construction and substantial improvement shall be constructed:

a. With materials and utility equipment resistant to flood damage;

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.

3. Elevation and Floodproofing. (See Larkspur Municipal Code Section 15.18.020 definitions for “New construction,” “Substantial damage” and “Substantial improvement.”)

a. Residential construction, new or substantial improvement, in any special flood hazard area (SFHA) Zone A or AE, shall have the lowest floor, including basement:

i. Elevated to a minimum of one (1) foot above the base flood elevation (BFE).

Upon the completion of the structure, the elevation of the lowest floor including basement shall be certified by a registered professional engineer or surveyor, or verified by the City Building Inspector to be properly elevated. Such certification or verification shall be provided to the Floodplain Administrator.

b. Nonresidential construction shall either be elevated to conform with subsection (A)(3)(a) of this section or, together with attendant utility and sanitary facilities:

i. Be floodproofed below the elevation recommended under subsection (A)(3)(a) 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 professional engineer or architect that the standards of this subsection (A)(3)(b) are satisfied. Such certification shall be provided to the Floodplain Administrator.

c. All new construction and substantial improvement 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 exceed the following minimum criteria:

i. Be certified by a registered professional engineer or architect; or

ii. Be certified to comply with a local floodproofing standard approved by the Federal Insurance Administration and Federal Emergency Management Agency; or

iii. Have a minimum of two (2) openings having a total net area of not less than one (1) square inch for every square foot of enclosed area subject to flooding. The bottom of all openings shall be no higher than one (1) foot above grade. Openings may be equipped with screens, louvers, valves or other coverings or devices; provided, that they permit the automatic entry and exit of floodwater.

d. Manufactured homes shall also meet the standards in subsection (D) of this section.

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.

1. All preliminary subdivision proposals shall identify the flood hazard area and the elevation of the base flood.

2. All subdivision plans will provide the elevation of proposed structure(s) and pad(s). If the site is filled above the base flood elevation, the final lowest as-built floor and pad elevations shall be certified by a registered professional engineer or surveyor and provided to the Floodplain Administrator.

3. All subdivision proposals shall be consistent with the need to minimize flood damage.

4. All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.

5. All subdivisions shall provide adequate drainage to reduce exposure to flood hazards.

6. All new subdivision proposals and other proposed development, including proposals for manufactured home parks and subdivisions, greater than fifty (50) lots or five (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:

i. Lowest floor elevation.

ii. Pad elevation.

iii. Lowest adjacent grade.

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

8. 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.

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

1. All manufactured homes that are placed or substantially improved on sites located: (a) outside of a manufactured home park or subdivision; (b) in a new manufactured home park or subdivision; (c) in an expansion to an existing manufactured home park or subdivision; or (d) in an existing manufactured home park or subdivision 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 City’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 that are placed or substantially improved on sites in an existing manufactured home park or subdivision within Zones A1-30, AH and AE on the City’s Flood Insurance Rate Map that are not subject to the provisions of this subsection (D) 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 thirty-six (36) inches in height above grade.

3. Upon 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 City Building Inspector to be properly elevated. Such certification and verification shall be provided to the Floodplain Administrator.

1. All recreational vehicles placed on sites within Zones A1-30, AH, and AE on the City’s Flood Insurance Rate Map will either:

a. Be on the site for fewer than one hundred eighty (180) consecutive days;

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 Larkspur Municipal Code Section 15.18.040 and the elevation and anchoring requirements for manufactured homes in subsection (D)(1) of this section.

2. Recreational vehicles placed on sites within Zones V1-30, V, and VE on the City’s Flood Insurance Rate Map will meet the requirements of subsections (E)(1) and (G) of this section.

F. Floodways. Located within areas of special flood hazard established in Larkspur Municipal Code Section 15.18.030(B) are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and erosion potential, the following provisions apply:

1. Prohibit encroachments, including fill, new construction, substantial improvement, and other new development, unless certification by a registered professional engineer or architect is provided demonstrating that encroachments shall not result in any increase in the base flood elevation during the occurrence of the base flood discharge.

2. If subsection (F)(1) of this section is satisfied, all new construction, substantial improvement, and other proposed new development shall comply with all other applicable flood hazard reduction provisions of this section.

G. Coastal High Hazard Areas. Within coastal high hazard areas as established under Larkspur Municipal Code Section 15.18.030(B), the following standards shall apply:

1. All new construction and substantial improvement shall be elevated on adequately anchored pilings or columns and securely anchored to such pilings or columns so that the lowest horizontal portion of the structural members of the lowest floor (excluding the pilings or columns) is elevated to or above the base flood level. The pile or column foundation and structure attached thereto are anchored to resist flotation, collapse, and lateral movement due to the effects of wind and water loads acting simultaneously on all building components. Water loading values used shall be those associated with the base flood. Wind loading values used shall be those required by applicable state or local building standards.

2. All new construction and other development shall be located on the landward side of the reach of mean high tide.

3. All new construction and substantial improvement shall have the space below the lowest floor free of obstructions or constructed with breakaway walls as defined in Larkspur Municipal Code Section 15.18.020. Such enclosed space shall not be used for human habitation and will be usable solely for parking of vehicles, building access or storage.

4. Fill shall not be used for structural support of buildings.

5. Manmade alteration of sand dunes which would increase potential flood damage is prohibited.

6. The Floodplain Administrator shall obtain and maintain the following records:

a. Certification by a registered engineer or architect that a proposed structure complies with subsection (G)(1) of this section.

b. The elevation (in relation to mean sea level) of the bottom of the lowest structural member of the lowest floor (excluding pilings or columns) of all new and substantially improved structures, and whether such structures contain a basement. (Ord. 1043 § 13, 2020; Ord. 976 § 10, 2011; Ord. 845 § 1 (part), 1993)