Single-Family Addition - Special Design Review

Special design review requirements

Verify the applicable zoning district, flood hazard areas and Base Flood Elevation(s) (BFEs) using GIS Map Viewer and FEMA Flood Map Service Center (MSC). The Map Viewer provides parcel detail to determine what government regulations and services are applicable to the parcel. While the MSC is the official public source for flood hazard information produced in support of the National Flood Insurance Program (NFIP). Parcel details can also be obtained from the Hillsborough County Property Appraiser website.

• Additional requirements apply for all properties located within the Special Flood Hazard Area. Any improvement to an existing structure requires a Substantial Damage/Improvement Worksheet.
• If the property is located within a Community Planned area, the areas require additional design review that govern the development per applicable code requirements
• If the property is located within a Coastal High Hazard Areas (Zone V) and Coastal A Zones or areas known to have muck soils, highly organic suspect soils, or where there is erosion, scour or settling of underlying soils, a soils and foundation analysis (geotechnical report) may be required
• If the property located inside the Wind-borne Debris Region, these areas require additional design requirements

Zoning

Unincorporated Hillsborough County has two (2) types of zoning districts, a standard zoning district and a Planned Development zoning district. Parcels located within a Community Planned Development (or Special Overlay District) area; these areas require additional architectural design review that govern the development per applicable code requirements.

All proposed projects located within Planned Development (PD) zoning districts must clearly demonstrate compliance with the criteria established within the conditions of approval, subdivision construction grading plan and must be consistent with the goals, policies and objectives contained within the Comprehensive Plan.

Special Flood Hazard Area (SFHA)

All properties located within the Special Flood Hazard Area (SFHA) shall have full compliance with the requirements of the Hillsborough County Construction Code, Hillsborough County Land Development Code, ASCE 24, the Florida Building Code and all other applicable laws and regulations that govern the standards set forth within the National Flood Insurance Program; most restrictive shall apply. 

If the property is located within a Coastal High Hazard Areas (Zone V) and Coastal A Zones or areas known to have muck soils, highly organic suspect soils, or where there is erosion, scour or settling of underlying soils on the property; more information may be required to ensure the project meets the applicable code requirements for all development within these areas.

Note: A soils and foundation analysis (geotechnical report) may be required to be provided by a Florida Registered Engineer that shows supporting information and a recommendation for the foundation design of the proposed structure.

Elevated structures within the SFHA

All enclosures (including an elevator shaft, a garage, or a crawlspace) of Areas Below Elevated Structures must be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Hydrostatic Flood Vents and flood resistant materials must be installed in compliance as per applicable code.

The total number of openings and the adequacy of the net open area of the openings depend on the type of opening and whether Engineered or Non-engineered openings are installed.

The following criteria must be met to satisfy the proper openings (hydrostatic flood vent) requirement:

• Every enclosed area is required to have a minimum of two flood openings of the exterior walls. Flood openings should be installed in at least two sides of each enclosed area, having a total net area of not less than 1 square inch for every square foot of enclosed area.
• The bottom of each flood opening must be positioned no higher than 1 foot above the highest interior or exterior adjacent grade below each opening.
• When multiple enclosed areas are present, each area must have openings in its exterior walls. In some situations, openings in interior walls or partitions may be required to ensure that floodwater can reach all enclosed areas and minimize unbalanced hydrostatic loads on interior and exterior walls. When openings are used in interior walls, the total number of openings and their net open area should be based on the size of the enclosed area, but openings in interior walls are not counted toward the required total opening requirement based on the exterior measurement of the enclosed area.
• Plans must reflect flood vents and flood resistant materials that will need to be installed in compliance as per applicable code. Area Calculations for flood opening; including the location / placement for the openings; the total square feet of the enclosed area below base flood elevation, the number of square inches required, and the number of square inches supplied.
• Engineered flood openings (Smart Vent, Flood Flaps, etc.) must be designed and certified by a registered design professional for a specific building and site-specific conditions; Provide the Florida Product Approvals and the ICC-ES Evaluation Reports that are provided by the International Code Council’s Evaluation Service (ICC-ES).
• Non-engineered openings require design detail to be shown on plans (turned block, weep holes, etc.)

Construction within the regulatory floodway

When floodways are designated within the SFHA on the Flood Insurance Rate Map or within the Flood Insurance Study, additional criteria will be met. Since the floodway is an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and erosion potential, notwithstanding any of the above, the following provisions shall apply:

• Any encroachment or placement of an obstruction is prohibited, including fill, any new construction, substantial improvements (includes replacement of an existing manufactured home, unless it is a DCA Certified modular home), mounded septic systems, docks, and other development unless it has been demonstrated through a no-impact analysis (hydrologic and hydraulic analyses that are also referred to as a No Rise Impact Analysis) with supporting technical data submitted by a State of Florida Registered Engineer demonstrating that the proposed encroachment shall not result in any increase in flood levels within the community during the occurrence of the base flood discharge. Background and analyses details shall be provided pursuant to the Federal Emergency Management Agency bulletins provided for said process. All new construction shall comply with all applicable flood hazard reduction provisions per the HC-LDC and those within the HCCC.
• The placement, or replacement, of any manufactured home, except in a pre-FIRM manufactured home park or subdivision that has not had a manufactured home flooded, is prohibited within the designated floodway.

Substantial improvement or damage to existing structures

Substantial Improvement Worksheets are required for all projects within the SFHA and shall comply with all applicable flood hazard reduction provisions; any alteration, repair, addition, reconstruction or improvements to a building shall have a Substantial Improvement Worksheet completed and uploaded with construction plans for review and recording with the permit application.

• Substantial improvement (SI); as defined in Title 44 of the Code of Federal Regulations § 59.1, means any reconstruction, rehabilitation, addition or other improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the “start of construction” of the improvement. This term includes structures that have incurred “substantial damage,” regardless of the actual repair work performed.
• Substantial damage (SD); as defined in Title 44 of the Code of Federal Regulations § 59.1, means damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.
• If the cost of improvement equals or exceeds 50 percent of the market value of the structure before the start of construction of the improvement, the project will be deemed a substantial improvement; then the existing structure must be evaluated to determine if the structure must be brought into compliance with all applicable laws and regulations for floodplain management and building code requirements.
• The cost of any previous work (during a 12-month period following the date of final inspection) shall also be added to the cost of the improvement, to include overhead and profit.

Note: A final Elevation Certificate on the current FEMA form will be required to be uploaded prior to project completion or Certificate of Occupancy for all development within the SFHAs.

Model dwelling units

• All Model Home development must meet the criteria pursuant to the HC-LDC Section(s) 6.11.62 and 10.01.05.C.8. Provide all items specified above to address construction lots for model dwelling units and parking.
• Provide ONE of the following:
• Alternate parking lot plan designed by a professional engineer or surveyor, OR
• Model home center parking lot site plan approval letter; OR
• Parking plan per the Transportation Technical Manual TD-19. Plan must include the lot with the parking layout and the ADA access from the parking lot to the model home.