(A) General standards. In all areas of special flood hazards, the following standards are required.
(1) Anchoring.
(a) All new construction and substantial improvements shall be anchored to prevent flotation, collapse or lateral movement of the structure.
(b) All manufactured dwellings must likewise be anchored to prevent flotation, collapse or lateral movement and shall be installed using methods and practices that minimize flood damage. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors. (Reference FEMA’s Manufactured Home Installation in Flood Hazard Areas guidebook for additional techniques.)
(2) Construction materials and methods.
(a) All new construction and substantial improvements shall be constructed with materials and utility equipment resistant to flood damage.
(b) All new construction and substantial improvements shall be constructed using methods and practices that minimize flood damage.
(c) Electrical, heating, ventilation, plumbing and air-conditioning equipment and other service facilities shall be designed and/or otherwise elevated or located so as to prevent water from entering or accumulating within the components during conditions of flooding.
(3) Utilities.
(a) All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system.
(b) New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the systems and discharge from the systems into floodwaters.
(c) On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding consistent with the State Department of Environmental Quality.
(4) Subdivision proposals.
(a) All subdivision proposals shall be consistent with the need to minimize flood damage.
(b) All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize or eliminate flood damage.
(c) All subdivision proposals shall have adequate drainage provided to reduce exposure to flood damage.
(d) Where base flood elevation data has not been provided or is not available from another authoritative source, it shall be generated for subdivision proposals and other proposed developments which contain at least 50 lots or five acres (whichever is less).
(5) Review of building permits. Where elevation data is not available either through the flood insurance study, FIRM or from another authoritative source (see § 153.078(C)(2)), applications for building permits shall be reviewed to assure that proposed construction will be reasonably safe from flooding. The test of reasonableness is a local judgment and includes use of historical data, high water marks, photographs of past flooding and the like, where available. Failure to elevate at least two feet above grade in these zones may result in higher insurance rates.
(6) AH Zone drainage. Adequate drainage paths are required around structures on slopes to guide floodwaters around and away from proposed structures.
(B) Specific standards. In all areas of special flood hazards where base flood elevation data has been provided (Zones A1-30, AH and AE) as set forth in §§ 153.077(B) or 153.078(C)(2), the following provisions are required.
(1) Residential construction.
(a) New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to a minimum of one foot above the base flood elevation.
(b) Fully enclosed areas below the lowest floor that are subject to flooding are prohibited or shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters.
(c) Designs for meeting this requirement must either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria.
1. A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided.
2. The bottom of all openings shall be no higher than one foot above grade.
3. Openings may be equipped with screens, louvers or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters.
4. If a building has more than one enclosed area below the lowest floor, each area shall be equipped with adequate flood openings.
(2) Nonresidential construction.
(a) New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall either have the lowest floor, including basement, elevated at or above the base flood elevation; or, together with attendant utility and sanitary facilities, shall:
1. Be floodproofed so that below the base flood level 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 professional engineer or architect that the design and methods of construction are in accordance with accepted standards of practice for meeting provisions of this division (B)(2) based on their development and/or review of the structural design, specifications and plans. Such certifications shall be provided to the official as set forth in § 153.078(C)(3)(b).
(b) Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in division (B)(1)(b) above.
(c) Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are one foot below the floodproofed level (e.g., a building floodproofed to the base flood level will be rated as one foot below).
(d) Applicants shall supply a comprehensive maintenance plan for the entire structure, including, but not limited to: exterior envelope of structure; all penetrations to the exterior of the structure; all shields, gates, barriers or components designed to provide floodproofing protection to the structure; all seals or gaskets for shields, gates, barriers or components; and the location of all shields, gates, barriers and components as well as all associated hardware and any materials or specialized tools necessary to seal the structure.
(e) Applicants shall supply an emergency action plan (EAP) for the installation and sealing of the structure prior to a flooding event that clearly identifies what triggers the EAP and who is responsible for enacting the EAP.
(3) Manufactured dwellings.
(a) Manufactured dwellings supported on solid foundation walls shall be constructed with flood openings that comply with division (A)(1)(b) above.
(b) The bottom of the longitudinal chassis frame beam in A Zones, shall be at or above BFE.
(c) The manufactured dwelling shall be anchored to prevent flotation, collapse and lateral movement during the base flood. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors.
(d) Electrical crossover connections shall be a minimum of 12 inches above BFE.
(e) Reference FEMA’s Manufactured Home Installation in Flood Hazard Areas guidebook for additional techniques.
(4) Recreational vehicles. Recreational vehicles placed on sites are required to:
(a) Be on the site for fewer than 180 consecutive days;
(b) Be fully licensed and ready for highway use, 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 requirements of division (B)(3) above and the elevation and anchoring requirements for manufactured dwellings.
(5) Small accessory structures. Relief from elevation or floodproofing as required in divisions (B)(1) or (B)(2) above may be granted for small accessory structures that are:
(a) Less than 200 square feet and do not exceed one story;
(b) Not temperature controlled;
(c) Not used for human habitation and are used solely for parking of vehicles or storage of items having low damage potential when submerged;
(d) Not used to store toxic material, oil or gasoline, or any priority persistent pollutant identified by the State Department of Environmental Quality unless confined in a tank installed in compliance with these Floodplain Overlay Zone regulations or stored at least one foot above base flood elevation;
(e) Located and constructed to have low damage potential;
(f) Constructed with materials resistant to flood damage;
(g) Anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood;
(h) Constructed to equalize hydrostatic flood forces on exterior walls by allowing for the automatic entry and exit of floodwater. Designs for complying with this requirement must be certified by a licensed professional engineer or architect or:
1. Provide a minimum of two openings with a total net area of not less than one square inch for every square foot of enclosed area subject to flooding;
2. The bottom of all openings shall be no higher than one foot above the higher of the exterior or interior grade or floor immediately below the opening; or
3. Openings may be equipped with screens, louvers, valves or other coverings or devices provided they permit the automatic flow of floodwater in both directions without manual intervention.
(i) Constructed with electrical and other service facilities located and installed so as to prevent water from entering or accumulating within the components during conditions of the base flood.
(6) Below-grade crawl spaces. Below-grade crawlspaces are allowed subject to the following standards as found in FEMA Technical Bulletin 11-01, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas.
(a) 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. Hydrostatic loads and the effects of buoyancy can usually be addressed through the required openings stated in division (B)(6)(b) below. Because of hydrodynamic loads, crawlspace 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. Other types of foundations are recommended for these areas.
(b) The crawlspace is an enclosed area below the base flood elevation (BFE) and, as such, must have openings that equalize hydrostatic pressures by allowing the automatic entry and exit of floodwaters. The bottom of each flood vent opening can be no more than one foot above the lowest adjacent exterior grade.
(c) 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 crawlspace used to elevate the building, but also any joists, insulation or other materials that extend below the BFE. The recommended construction practice is to elevate the bottom of joists and all insulation above BFE.
(d) Any building utility systems within the crawlspace must be elevated above BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions. Ductwork, in particular, must either be placed above the BFE or sealed from floodwaters.
(e) The interior grade of a crawlspace below the BFE must not be more than two feet below the lowest adjacent exterior grade.
(f) The height of the below-grade crawlspace, measured from the interior grade of the crawlspace to the top of the crawlspace foundation wall must not exceed four feet at any point. The height limitation is the maximum allowable unsupported wall height according to the engineering analyses and building code requirements for flood hazard areas.
(g) There must be an adequate drainage system that removes floodwaters from the interior area of the crawlspace. The enclosed area should be drained within a reasonable time after a flood event. The type of drainage system will vary because of the site gradient and other drainage characteristics, such as soil types. Possible options include natural drainage through porous, well-drained soils and drainage systems such as perforated pipes, drainage tiles or gravel or crushed stone drainage by gravity or mechanical means.
(h) The velocity of floodwaters at the site should not exceed five feet per second for any crawlspace. For velocities in excess of five feet per second, other foundation types should be used.
(7) Additional information. For more detailed information, refer to FEMA Technical Bulletin 11-01.
(C) Before regulatory floodway. In areas where a regulatory floodway has not been designated, no new construction, substantial improvements or other development (including fill) shall be permitted within Zones A1-30 and AE on the community’s FIRM unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than one foot at any point within the community.
(D) Floodways. Located within areas of special flood hazard established in § 153.077(B) are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles and erosion potential, the following provisions apply.
(1) Except as provided in division (D)(3) below, encroachments are prohibited, including fill, new construction, substantial improvements and other development unless certification by a registered professional civil engineer is provided demonstrating through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge.
(2) If division (D)(1) above is satisfied, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of this section.
(3) Projects for stream habitat restoration may be permitted in the floodway, provided:
(a) The project qualifies for a Department of the Army, Portland District Regional General Permit for Stream Habitat Restoration (NWP-2007-1023);
(b) A qualified professional (a registered professional engineer; or staff of NRCS; the county; or fisheries, natural resources or water resources agencies) has provided a feasibility analysis and certification that the project was designed to keep any rise in 100-year flood levels as close to zero as practically possible given the goals of the project;
(c) No structures would be impacted by a potential rise in flood elevation; and
(d) An agreement to monitor the project, correct problems and ensure that flood-carrying capacity remains unchanged is included as part of the local approval.
(4) Temporary structures placed in the floodway: Relief from no-rise evaluation, elevation or dry floodproofing standards may be granted for a nonresidential structure placed during the dry season (June to October) and for a period of less than 90 days. A plan for the removal of the temporary structure after the dry season or when a flood event threatens shall be provided. The plan shall include disconnecting and protecting from water infiltration and damage all utilities servicing the temporary structure.
(5) Temporary storage of goods and materials, not including hazardous materials, is allowed in the floodway for a period of less than 90 days within the dry season (June to October).
(E) Standards for shallow flooding areas (AO Zones). Shallow flooding areas appear on FIRMs as AO Zones with depth designations. The base flood depths in these zones range from one to three feet above ground where a clearly defined channel does not exist, or where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is usually characterized as sheet flow. In these areas, the following provisions apply.
(1) New construction and substantial improvements of residential structures and manufactured dwellings within AO Zones shall have the lowest floor (including basement) elevated above the highest grade adjacent to the building, a minimum of one foot above the depth number specified on the FIRM (at least two feet if no depth number is specified).
(2) New construction and substantial improvements of nonresidential structures within AO Zones shall either:
(a) Have the lowest floor (including basement) elevated above the highest adjacent grade of the building site, one foot or more above the depth number specified on the FIRM (at least two feet if no depth number is specified); or
(b) Together with attendant utility and sanitary facilities, be completely floodproofed to or above that level so that any space below that level is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. If this method is used, compliance shall be certified by a registered professional engineer or architect as in division (B)(2)(c) above.
(3) Adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures are required.
(4) Recreational vehicles placed on sites within AO Zones on the community’s FIRM either:
(a) Be on the site for fewer than 180 consecutive days;
(b) Be fully licensed and ready for highway use, 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 requirements of division (E)(1) above and the elevation and anchoring requirements for manufactured dwellings.
(F) Critical facilities. Construction of new critical facilities shall be, to the extent possible, located outside the limits of the Special Flood Hazard Area (SFHA) (100-year floodplain). Construction of new critical facilities shall be permissible within the SFHA if no feasible alternative site is available. Critical facilities constructed within the SFHA shall have the lowest floor elevated three feet above BFE or to the height of the 500-year flood, whichever is higher. Access to and from the critical facility should also be protected to the height utilized above. Floodproofing and sealing measures must be taken to ensure that toxic substances will not be displaced by or released into floodwaters. Access routes elevated to or above the level of the base flood elevation shall be provided to all critical facilities to the extent possible.
(Ord. 1267, passed 1-3-2012; Ord. 1283, passed 12-4-2018)