Stormwater/Drainage Requirements for Residential Construction

Applicability

The following requirements apply for all new residential structures or substantial improvements to existing residential structures that are built in a regulatory floodplain and/or FEMA special flood hazard areas (SFHA). Substantial improvements are improvements that exceed 50% of the structure’s value. No construction or improvements are allowed within a designated floodway or an erosion hazard setback area.Find my floodzone

Prior to the issuance of a Certificate of Occupancy, a FEMA Elevation Certificate is required to demonstrate compliance with regulatory flood elevation requirements. For additional information you may also review this brochure, entitled “Developing Your Floodplain Property”

SITE BUILT RESIDENTIAL STRUCTURES

Floodplain Use Permit is Required
All proposed structures must have the lowest floor, including basement, elevated to, or above, the Regulatory Flood Elevation.
- In an AO Zone, all proposed structures must be elevated to one (1) foot minimum above the number indicated on the FIRM panel or a minimum of two (2) feet if no number is specified.
- In an A Zone where a base flood elevation (BFE) has not been determined, generally, a minimum elevation of two (2) feet above the highest adjacent grade is required for all proposed structures. These structures may also instead be elevated in accordance with the criteria developed by the Director of the Arizona Department of Water Resources.
- In Zones AE, AH and Al-30, all structures must be elevated to one (1) foot above the base flood elevation.
No floodproofing is required for properly elevated site-built residential structures.

MANUFACTURED HOMES AND STORAGE TANKS

Floodplain Use Permit is Required
Must meet all State of Arizona Office of Manufactured Housing requirements set forth in the Minimum Standard for Manufactured Housing Foundation in Floodplains (PDF). This includes the following:
- Manufactured Home shall be placed parallel to the direction of flow
- Foundations, or fill pad erosion protection shall be designed by an Arizona Registered Professional Civil Engineer and approved by all appropriate local governmental agencies and by the Office of Manufactured Housing
- The home shall be elevated so that the bottom of the structural frame (I-beam) or the lowest point of any attached utility (this includes duct work and ground mounted air conditioning units), whichever is lower, is elevated at or above the regulatory flood elevation
- The home must be securely anchored to an adequately anchored foundation system to resist flotation, collapse or lateral movement. Methods of anchoring may include, but are not to be limited to, use of over-the top or frame ties to ground anchors. This requirement is in addition to applicable state and local anchoring requirements for resisting wind forces.
- An Arizona licensed installer or an Arizona Registered Professional Civil Engineer must certify that the installation of a manufactured home meets all of the requirements of the Floodplain Use Permit.

RECREATIONAL VEHICLES

Must be on site for fewer than 180 consecutive days and 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 to a physical site.
OR
Obtain a floodplain use permit and be securely anchored to an adequately anchored foundation system to resist flotation, collapse or lateral movement. Methods of anchoring may include, but are not to be limited to, use of over-the top or frame ties to ground anchors. This requirement is in addition to applicable state and local anchoring requirements for resisting wind forces.

DETACHED ACCESSORY RESIDENTIAL STRUCTURES, NOT FOR HABITATION

Accessory residential structures, not for habitation, must either follow the elevation requirements specified for site built residential construction or be designed and constructed so that:

Any portion of the accessory structure below the regulatory flood elevation is built using flood-resistant materials
The accessory structure is adequately anchored to prevent flotation, collapse and lateral movement
Any mechanical and utility equipment in the accessory structure must be elevated or flood-proofed to or above the regulatory flood elevation
The accessory structure must be designed to allow for the automatic entry and exit of flood waters

APPLICABLE ADOPTED STANDARDS

The County has adopted ADWR STANDARD 6-05 - "Development of individual Residential Lots within Flood-prone Areas,” which provides guidelines for site plans for individual residential lots to be used for all new construction.