B-47 2020-Current: Residential Construction in Floodzones

The purpose of the following information and documents are to clarify procedures used by the Sonoma County Permit & Resource Management Department to enforce provisions of Sonoma County Code Chapter 7B-Flood Damage Prevention, CRC R322-Flood Resistant Construction, and ASCE24-Flood Resistant Design and Construction. These procedures have been in place since January, 1982, when the department first received flood insurance rate maps, floodway maps and the attendant certification requirements.

Version: 04/01/2020
Effective Date: 09/03/2019

Glossary of Terms Used in This Section

Base Flood Elevation (BFE) - The flood elevation having a one-percent chance (100-Year Flood) of being equaled or exceeded in any given year. The BFE is determined by statistical analysis for each local area and designated on the Flood Insurance Rate Maps.

Flood Insurance Rate Maps (FIRM) - The official map of a community issued by FEMA, that shows the Base Flood Elevation (BFE), along with the Special Flood Hazard Areas (SFHA) and the risk premium zones applicable to the community.

Special Flood Hazard Area (SFHA): the land in the floodplain subject to a one percent (1%) or greater chance of flooding in any given year delineated on the FIRM

Flood Vents - A system designed to allow floodwaters to enter an enclosure, usually the foundation walls, so that the rising water does not create a dangerous differential in hydrostatic pressure.

Floodway - The central portion of the floodplain that carries the greatest portion of the waterflow in a flood. Obstructions in the floodway will result in increased flood levels upstream. The Floodway is also known as F1 Floodway Combining District for Zoning regulations.

Lowest Floor - The lowest floor of the lowest enclosed area, including basements; however, an un- finished or flood-resistant enclosure used solely for parking, building access, or storage shall not be considered the lowest floor.

National Flood Insurance Program (NFIP) - The federal program created by an act of Congress in 1968 that makes flood insurance available in communities that enact satisfactory floodplain management regulations.

Technical Details

1. Adopted Flood Map & Floodplain Management Regulations: Floodplain management regulations are contained in Chapter 7B of the Sonoma County Code. These regulations were enacted when Sonoma County voluntarily elected to participate in the National Flood Insurance Program. This program allows reasonably priced flood insurance to be offered. The flood level referred to is the Base Flood Elevation (BFE), as published on the Flood Insurance Rate Maps (FIRM) by the Federal Emergency Management Agency (FEMA).
2. Application: The lowest floor for all new construction and substantial improvements of residential living areas, utility areas, or any enclosed area including basement must be at least one foot above the BFE. Only non-habitable areas used solely for vehicle parking, building access, or limited storage (R322.1.5) that are not subject to flood damage may be allowed below the base flood elevation and must be clearly labeled as such on the drawings submitted for building permits.
3. Flood Resistant Materials: All building materials and assemblies located below the BFE must be resistant to flood damage. Materials that are approved for use below the base flood elevation include masonry, concrete, pressure treated heavy timber, pressure treated wood or some combination. Connectors and fasteners in contact with pressure treated wood products must be either hot-dipped galvanized or stainless steel. No enclosed stud spaces or cavities will be approved below the base flood elevation. All building components below the BFE must be designed to be rinsed clean of sediment after a flood. Similarly, joist spaces enclosed by plywood or sheetrock on top and bottom will not be approved. FEMA Technical Bulletins 1-93, 2-93, 5-93, 8-96, and 11-01 (available on the FEMA website) provide additional information on the acceptability of various materials and construction methods used below the BFE.
4. Assemblies: Assemblies, other than wood stud frame, such as pole buildings, may be brought to PRMD for preliminary review prior to an application for a building permit being submitted. Conformance with flood regulations may be discussed before design time is expended on concepts that may not be approved. In general braced post and beam construction, with no enclosed stud space, is an acceptable type of construction. New dwellings, located in the State Responsibility Area (SRA), must maintain the ignition-resistant integrity of the exterior walls, on the underside of the floors, or the entire underfloor area shall be enclosed to grade. Where enclosed space occurs below the BFE, openings are required to allow for automatic entry and exit of floodwaters. These openings are also referred to as flood vents and shall meet the following minimum requirements:
   1. A minimum of two openings on different sides of each enclosed area. If a structure has more than one enclosed area below the BFE, each area shall have openings on exterior walls.
   2. The total net area of all openings shall be at least one square inch for each square foot of enclosed area.
   3. The bottom of each opening shall be no more than one foot above the adjacent ground level.
   4. Openings shall not be less than three inches in diameter.
   5. Louvers, screens, or other opening covers shall not block or impede the automatic flow of floodwaters into and out of the enclosed areas.
   6. Openings meeting the requirements of a through e above may be installed in doors and windows. Doors and windows by themselves do not meet the flood venting requirements.
5. Design Loads: Construction must be designed for all vertical and lateral loads. When a building site is subject to flowing water, the structure must be designed to resist those forces. Structures located in Special Flood Hazard zones, where the water velocity exceeds 5 feet per second, must be designed to resist the hydrodynamic force of moving water. PRMD will use the FIRM to determine if moving water design is required for a building site. Most people assume that the velocity in the fringe is lower than the velocity in the floodway; however, this may not always be correct. We recommend that you design for Floodway Velocity. Please refer to FEMA technical literature on “Design for Hydrodynamic Forces.”
6. Fire-Resistant Construction Required by the California Residential Code R302.6: A common residential design for the Sonoma County flood zone is a garage or carport located below the BFE that supports living space located above the base flood elevation. Fire-resistant construction is required by CRC R302.6 between garages and living areas. Floor-ceiling construction must use 5/8" Type” “X” sheetrock on the ceiling of the garage, if there is a living space above the garage. The entire assembly must be above the base flood elevation. The use of moisture resistant 5/8" Type “X” sheetrock for fire-resistant construction located below the BFE will not be approved.
   
   Additionally in a typical garage/dwelling separation all ceilings that are required to have 5/8” Type “X” sheetrock, are required to be supported with walls sheathed with minimum ½” gypsum. However, enclosed stud cavities are not permitted in areas below the BFE. A common solution is the use of heavy timber construction at the garage/storage space to support the floor above. Columns are a minimum 8x8 and all girders/headers/beams supporting the floor above are 6x10 nominal dimensions.
   
   All materials below the BFE are required to be flood resistant as in Item #3 above. If there are no enclosed stud cavities, ¾” Stucco/Portland Cement-Sand Plaster provides equivalent fire resistance as ½” gypsum (CBC Table 722.2.1.4(2))
7. Electrical Limitations: PG&E must approve the location of all electrical meter locations. Both electrical meter sockets and load centers must have 30 inch wide and 36 inch deep working clearances. If located on an exterior platform, this platform must be safe and conform to the current version of the California Building Code. If the load center is located inside the building it may not be located in a closet used to store combustible materials and must conform to the current version of the National Electrical Code in every respect.
   
   All electrical equipment must be located above the BFE. “Electrical equipment” includes electrical load centers, subpanels, circuit breakers, ground fault interrupting devices, motors, etc. Therefore, load centers with circuit breakers must be located above the BFE.
   
   Electrical branch circuits may extend below the BFE only if protected by a ground fault interrupting device which is located above the BFE. Since no enclosed stud spaces may be approved below the BFE, protection of electrical conductors must usually be done with approved conduit.
   
   An electrical meter socket may be located below the BFE. If this option is chosen, PG&E will require a main disconnect located within four feet of the meter. A main disconnect located below the BFE may not be a circuit breaker. The remaining components of the service equipment must be located above the BFE.
8. Plumbing & Mechanical Limitations: All plumbing and mechanical equipment must be located above the BFE. “Plumbing and mechanical equipment” includes all heaters, furnaces, air conditioners, compressors, fans, water heaters, laundry facilities, plumbing fixtures, etc. Toilets and therefore toilet rooms are also prohibited below the BFE.
9. Limitations on Storage: In general the lowest floor of all enclosed storage rooms and areas must be located one foot above the BFE. The enclosed storage or parking space that may be permitted below the BFE is only that which is incidental and accessory to the principal use of the structure and used only to store damage resistant items that can not be stored above the base flood elevation. For instance, if the structure is a residence, storage in the enclosure should be limited to items such as lawn and garden equipment, snow tires, canoes, and other low damage items that cannot be stored in the elevated portion of the structure. The term “low damage items” is a good test of acceptability. If an item may be stored outdoors during bad weather or immersed under water without damage, it might be acceptable to store it in an enclosed area below the base flood elevation. The occupant should note that no flood insurance coverage is available for these items under most circumstances. Plans submitted for plan check must include the following statement limiting the use of storage space or garages located below the base flood elevation: Use of enclosed storage areas or garages below the Base Flood Elevation must meet all the following limitations: a. Use of this storage area must be incidental & accessory to the principal use of the structure, and b. Storage is limited to damage resistant items only, and c. Storage is limited to items that can not be stored above the base flood elevation.
10. Floodways: Located within the SFHA are areas designated as floodways. Since the floodways are extremely hazardous due to the velocity of flood waters that carry debris, potential projectiles, and erosion potential, building and grading permits are extremely restricted. New construction is not allowed within a floodway, however elevation of existing structures is allowed when design provisions for moving water are provided. Please contact PRMD Planning Section regarding construction limitations in the F1 Floodway Combining District and see policy 8-1-12 Construction Limitations in the F-1 Floodway
11. Other Information: Information on flood insurance is available from the NFIP by phone or on their Internet site. ( https://www.fema.gov/national-flood-insurance-program) Elevation Certificates (FEMA Form 086-033) can be obtained online at https://www.fema.gov/media- library/assets/documents/160 Technical questions about flood regulations may be answered by FEMA, Region IX.

Elevation Certificate Procedure

1. Site Review & Notice to Applicant: When an application for the construction of a building or a manufactured home (mobile home) installation is received by PRMD, a site evaluation is made to identify any known hazard. If the building site is within the SFHA as shown on the FIRM, an Elevation Certificate (FEMA Form 086-033) will be required. After the site evaluation, the applicant will be notified of this requirement.
2. Site Plan, Section Drawings, & Survey Information: The applicant must retain a registered civil engineer or licensed surveyor to determine the actual reference elevation of the site where the building is proposed. A benchmark indicating the elevation above the North American Vertical Datum 1988 (NAVD 88) must be placed at the site for use during construction. The elevation of the benchmark and the building pad must be determined by running a survey line using a closed loop level circuit from an established and approved benchmark. Before the building plans can be approved and a permit issued, a site plan and section drawings prepared by a licensed surveyor or engineer with following information must be submitted:
   1. The location and elevation of the NAVD 88 benchmark.
   2. The elevation of the building pad.
   3. The proposed elevation of the “lowest floor” or the reference level.
   4. Section drawings that include:
      1. The location of the BFE as read from the most recently adopted FIRM.
      2. The finished floor elevation which must be 1’ above the BFE
      3. Lowest adjacent grade next to building
   5. All plumbing, electrical, and mechanical equipment must be shown on the plans and installed above the BFE.
3. Verification of Floor and Reference Level Elevation: After the building permit is issued, the builder uses the benchmark on site to construct the building floor or reference level to the correct elevation. When the floor framing is complete, the surveyor or engineer must survey the floor and reference level and complete their sections of the FEMA Elevation Certificate. Section B will already have been completed by the engineer or surveyor and verified by PRMD staff. If the reference level is not the lowest floor, this should be noted or explained on the plans or Elevation Certificate or both. The partially completed Elevation Certificate shall be available on- site for the Inspector's review at the time of the close-in inspection. The fully completed Elevation Certificate shall be provided to the Inspector at the time of the final inspection. This must be done before occupancy of the building.

Improvements/Repairs to Existing Non-Elevated Buildings in Flood Hazard Areas

When existing structures are repaired after being damaged or voluntarily improved (i.e. additions/remodels/repairs), the scope of work may require the structure to be elevated. Chapter 7B of the Sonoma County Code establishes thresholds for residential construction based on the percentage of repair or improvement and when elevation of a structure is required. These thresholds are called ‘Substantial Improvement’ and/or ‘Substantial Damage’. PRMD policy 1-4-4 Flood Elevation Policy contains a summary of requirements and the procedure for computing the percentage of improvements and if that threshold has been met.

When work is proposed to non-elevated structures, applicants shall complete the form CNI-003 with their application. This form documents the proposed construction costs of the project.

FEMA R-758, Substantial Improvement/Substantial Damage Desk Reference provides guidelines for determining whether remodels/additions/repairs constitutes Substantial Improvement or Damage and whether elevation of the structure is required.

Structures that need to be elevated will need to follow the elevation procedure above.

Additions: Additions to non-elevated structures are required to have the addition portion constructed above the BFE. Depending upon the scope of the addition, it may be required that the entire existing structure be elevated if it is considered a ‘Substantial Improvement’. (Chapter 7B)

Fire-resistant construction requirements near property lines: New constructed/rebuilt walls or stairs constructed within 5’ of a property line of a non-sprinklered building or 3’ of a property line of a sprinklered building, are required to comply with the fire-resistant construction requirements of R302.1

Availability of Emergency Access: Due to the height of the elevated structure per the amended Sonoma County Fire Code, buildings greater than 30 feet from fire access points shall be equipped with fire sprinklers or shall have a minimum of two means of egress from a third floor. This can be accomplished by an escape ladder or by stair access. (Sonoma County Code Sec. 13-29)

F1, Floodways: Structures in F1, Floodways may be elevated but must comply with policy 8-1-12 Construction Limitations in the F-1 Floodway

References

• Sonoma County Code Chapter 7B
• Policies and Procedures
• Permit Sonoma Instructions and Forms
• California Residential Code
• Flood Insurance Rate Maps