Concord Municipal Code Art. IV Provisions for Flood Hazard Reduction

In all areas of special flood hazards the following standards are required:

(a) 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.

(b) Construction Materials and Methods. All new construction and substantial improvements of structures, including manufactured homes, shall be constructed:

(1) With flood resistant materials, and utility equipment resistant to flood damage for areas below the base flood elevation;

(2) Using methods and practices that minimize flood damage;

(3) With electrical, heating, ventilation, plumbing and air conditioning equipment and other service facilities elevated to, or above, the BFE or depth number specified on the FIRM; and

(4) 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.

(c) Elevation and Floodproofing.

(1) Residential construction. All new construction or substantial improvements of residential structures shall have the lowest floor, including basement:

a. In AE, AH, A1-30 Zones, elevated to 1 foot or more above the base flood elevation.

b. In an AO zone, elevated above the highest adjacent grade to a height equal to or exceeding 1 foot above 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.

c. In an A zone, without BFE’s specified on the FIRM [unnumbered A zone], where the BFE’s have been determined pursuant to subsection 15.75.140(c), elevated as required in subsection 15.75.170(c)(1)a.

d. In an A zone, without BFE’s specified on the FIRM [unnumbered A zone], where the BFE’s have not otherwise been determined, the following requirements shall apply:

1. Single parcels – Elevate the lowest floor of any residential structure to no less than two feet above natural grade when base flood elevation is not established.

2. Multiple parcels (five or more) – All proposals shall establish the 100-year base flood elevation before the first consideration of any plan or permit for construction or development of the parcels. The city may require standards for subdivisions in excess of those identified elsewhere in this chapter.

Upon the completion of the forms for the structure’s foundation, and prior to pouring the foundation, the elevation of the lowest flood, including basement, shall be certified by a registered civil engineer or licensed land surveyor, and verified by the building division to be properly elevated. Such certification and verification shall be provided to the Floodplain Administrator.

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 division to be properly elevated. Such certification and verification shall be provided to the Floodplain Administrator.

(2) Nonresidential construction. All new construction or substantial improvements of nonresidential structures shall either be elevated to conform with subsection 15.75.170(c)(1) or:

a. Be floodproofed, together with attendant utility and sanitary facilities, below the elevation recommended under subsection 15.75.170(c)(1), so that the structure is watertight with walls substantially impermeable to the passage of water;

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

c. Be certified by a registered civil engineer or architect that the standards of subsections 15.75.170(c)(2)a and 15.75.170(c)(2)b are satisfied. Such certification shall be provided to the Floodplain Administrator.

(3) Floodproofing. Nonresidential construction shall either be elevated in conformance with subsections 15.75.170(c)(1) or 15.75.170(c)(2) or, together with attendant utility and sanitary facilities, be floodproofed to the base flood elevation. Examples of floodproofing include, but are not limited to:

a. Installation of watertight doors, bulkheads, and shutters;

b. Reinforcement of walls to resist water pressure;

c. Use of paints, membranes, or mortars to reduce seepage through walls;

d. Addition of mass or weight to structure to resist flotation;

e. Armor protection of all fill materials from scour and/or erosion;

f. Certification provided to the city by a registered professional engineer or architect that the standards of this subsection are satisfied.

g. For all new construction and substantial improvements, fully enclosed areas below the lowest floor that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement shall either be certified by a registered professional engineer or architect or shall meet or exceed the following minimum criteria: 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. The bottom of all openings shall be no higher than one foot above grade. Openings may be equipped with screens, louvers, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.

(4) 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 shall meet the following minimum criteria:

a. For non-engineered openings:

1. 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;

2. The bottom of all openings shall be no higher than one foot above grade;

3. 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

4. Buildings with more than one enclosed area shall have openings on exterior walls for each area to allow flood water to directly enter; or

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

(5) Manufactured homes. See section 15.75.200.

(6) Garages and low cost accessory structures.

a. Attached garages.

1. A garage attached to a residential structure, constructed with the garage floor slab below the BFE, shall be designed to allow for the automatic entry of flood waters. See subsection 15.75.170(c)(4). Areas of the garage below the BFE shall be constructed with flood resistant materials. See subsection 15.75.170(b).

2. A garage attached to a nonresidential structure shall meet the above requirements or be dry floodproofed. For guidance on below grade parking areas, see FEMA Technical Bulletin TB 5.25.030.

b. Detached garages and accessory structures.

1. “Accessory structures” used solely for parking (2 car detached garages or smaller) or limited storage (small, low-cost sheds), as defined in Article II of this chapter, 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:

i. Use of the accessory structure shall be limited to parking or limited storage;

ii. The portions of the accessory structure located below the BFE shall be built using flood-resistant materials;

iii. The accessory structure shall be adequately anchored to prevent flotation, collapse and lateral movement;

iv. Any mechanical and utility equipment in the accessory structure shall be elevated or floodproofed to or above the BFE;

v. The accessory structure shall comply with floodplain encroachment provisions in section 15.75.210; and

vi. The accessory structure shall be designed to allow for the automatic entry of flood waters in accordance with subsection 15.75.170(c)(4).

2. Detached garages and accessory structures not meeting the above standards shall be constructed in accordance with all applicable standards in section 15.75.170.

(7) Crawl Space Construction. This subsection applies to buildings with crawl spaces up to 2 feet below grade. Below-grade crawl space construction in accordance with the requirements listed below will not be considered basements.

a. The building shall 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. Crawl space construction is not allowed in areas with flood velocities greater than 5 feet per second unless the design is reviewed by a qualified design professional, such as a registered civil engineer;

b. The crawl space is an enclosed area below the BFE and, as such, shall have openings that equalize hydrostatic pressures by allowing for the automatic entry and exit of floodwaters. For guidance on flood openings, see FEMA Technical Bulletin TB 1-08;

c. Portions of the building below the BFE shall be constructed with materials resistant to flood damage. This includes not only the foundation walls of the crawl space used to elevate the building, but also any joists, insulation, or other materials that extend below the BFE; and

d. Any building utility systems within the crawl space shall be elevated above BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions.

e. Requirements for all below-grade crawl space construction, in addition to the above requirements, to include the following:

1. The interior grade of a crawl space below the BFE shall not be more than 2 feet below the lowest adjacent exterior grade (LAG), shown as D in figure 3 of Technical Bulletin TB 11-01;

2. The height of the below-grade crawl space, measured from the interior grade of the crawl space to the top of the crawl space foundation wall shall not exceed 4 feet (shown as L in figure 3 of Technical Bulletin TB 11-01) at any point;

3. There shall be an adequate drainage system that removes floodwaters from the interior area of the crawl space within a reasonable period of time after a flood event, not to exceed 72 hours; and

4. The velocity of floodwaters at the site should not exceed 5 feet per second for any crawl space. For velocities in excess of 5 feet per second, other foundation types shall be used.

(8) Standards for storage of materials and equipment.

a. The storage or processing of materials that are in time of flooding, buoyant, flammable, explosive, or could be injurious to human, animal, or plant life is prohibited.

b. Storage of other material or equipment may be allowed if not subject to major damage by floods and firmly anchored to prevent flotation or if readily removable from the area within the time available after flood warning.

(Code 2002, § 34-91. Ord. No. 10-1)

(a) All new and replacement water supply and sanitary sewage systems shall be designed to minimize or eliminate:

(1) Infiltration of flood waters into the systems; and

(2) Discharge from the systems into flood waters.

(b) On site waste disposal systems shall be located to avoid impairment to them, or contamination from them during flooding.

(Code 2002, § 34-92. Ord. No. 10-1)

(a) All subdivision proposals and other proposed development, including proposals for manufactured home parks and subdivisions, shall:

(1) Identify the Special Flood Hazard Areas (SFHA) and Base Flood Elevations (BFE).

(2) Identify the elevations of lowest floors of all proposed structures and pads on the final plans.

(3) 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:

a. Lowest floor elevation.

b. Pad elevation.

c. Lowest adjacent grade.

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

(c) 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.

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

(Code 2002, § 34-93. Ord. No. 10-1)

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 shall:

(a) Within Zones A, AO, 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 1 foot or more above the base flood elevation and be securely fastened to an adequately anchored foundation system to resist flotation, collapse, and lateral movement in accordance with one of the following methods:

(1) By providing an anchoring system designed to withstand horizontal forces of 15 pounds per square foot and uplift forces of nine pounds per square foot; or

(2) By the anchoring of the unit’s system designed to be in compliance to the Department of Housing and Urban Development Mobile Home Construction and Safety Standards; or

(3) By bolting the frame or undercarriage to a reinforced, permanent foundation such as a retaining wall or storm wall used to set the unit.

As set forth in section 15.75.160, certification meeting the standards above is required of the installer or state agency responsible for regulating the placement, installation, and anchoring of individual manufactured home units.

(b) Provide adequate surface drainage and access for a hauler;

(c) Place all manufactured homes on pads or lots elevated on compacted fill or on pilings so that the lowest floor of the manufactured home is elevated to 1 foot or more above the base flood elevation. If elevated on pilings:

(1) The lots shall be large enough to permit steps;

(2) The pilings shall be placed in stable soil no more than ten feet apart; and

(3) Reinforcement shall be provided for pilings more than six feet above ground level.

(d) No new manufactured home shall be placed or substantially improved in a floodway.

(e) Certification of compliance is required of the developer responsible for the plan or state agency responsible for regulating manufactured home placement.

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 inspector to be properly elevated. Such certification and verification shall be provided to the Floodplain Administrator.

(Code 2002, § 34-94. Ord. No. 10-1)

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:

(a) 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; or establish a setback from the stream bank equal to five times the width of the stream at the top of the bank or 20 feet on each side from the top of the bank, whichever is greater.

(b) 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.

(c) If subsections 15.75.210(a) and 15.75.210(b) are satisfied, all new construction, substantial improvement, and other proposed new development shall comply with all other applicable flood hazard reduction provisions of this Article IV.

(Code 2002, § 34-95. Ord. No. 10-1)