The Town of Hilton Head Island participates in the National Flood Insurance Program (NFIP) to ensure that Federal flood insurance is available to all residents in the community. As a requirement of the NFIP the Town has adopted local ordinances to manage development so that future flood damage is minimized within the areas of the Island subject to the risk of periodic flooding. This area is delineated on Flood Insurance Rate Maps (FIRMS). It is referred to as the 100 year floodplain and covers more than eighty percent of the Island. Zones of the 100 year floodplain on the FIRM designated as "A" are subject to rising water with moderate tidal flooding and moderate wind. Zones designated as "V" are subject to strong winds and waves more than 3 feet in addition to tidal flooding.
Floodplains perform important natural and beneficial functions. These include temporarily storing flood water, protecting water quality, recharging groundwater and preventing erosion. Floodplains provide habitat for wildlife, open space for recreation and buffers of native vegetation to preserve the aesthetic beauty of the Island. Floodplains and their associated wetlands should be preserved and protected.
When development does occur in a 100 year floodplain the NFIP requires that the Town issue a permit. Development includes any grading, filling, dredging, subdivision of land or the construction or improvement of structures. Development may not begin until all Federal, State and local permits are issued. Proposed development should be the minimum necessary for the project so that the risk of flooding is not increased and flood water is not diverted on to adjacent property. All structures must be constructed to minimize any potential damage from flooding. Construction regulations for commercial and residential structures are contained in the current edition of the International Code Series and Title 15, Chapter 9 of the Town of Hilton Head Municipal Ordinance.
Damage to new and substantially improved structures in a 100 year floodplain will be minimized when the structure is elevated above the level required on the Flood Insurance Rate Map. The use of enclosed areas below the first elevated floor is strictly limited to parking, storage or building access. All enclosures must have at least two vents on two different walls to allow water to move freely so pressure on both sides of the walls is equalized. One square inch of vent opening is required for every square foot of area of the enclosure. The vents must be within one foot of grade. Construction materials used for any portion of the building below the base flood elevation must be classified as flood resistant and may not sustain damage when submerged in flood water. All electrical receptacles and devices such as heat pumps, air conditioners, hot water heaters, and plumbing fixtures such as toilets, sinks, tubs and showers must be elevated above the base flood elevation. Propane gas tanks must be elevated or firmly anchored to foundations to prevent flotation or lateral movement.
Zones designated as "V" on the Flood Insurance Rate Map and commonly called "velocity zones" are areas where hazards exist in addition to coastal flooding due to high wind, storm surge and strong wave action. There are special construction requirements in these zones. Buildings must be elevated on pilings or columns so that the bottom of the lowest supporting floor structure is above the base flood elevation. The area below that floor must be kept open to allow the free movement of water under the structure. Special break away walls designed to collapse without causing damage to the building may be constructed. Propane gas tanks must be elevated or securely buried below the line of potential erosion.
To verify that a building has been properly elevated the Town requires that a preliminary Elevation Certificate marked "under construction" be submitted after the lowest floor is in place. This form is signed by a Registered Engineer or Land Surveyor and it becomes part of the permanent Building Permit record. A final Elevation Certificate marked "finished construction" must be submitted completely filled out, signed and sealed prior to any legal occupancy of the building. In addition to the Elevation Certificate the owner of any new or substantially improved building or addition with a crawl space having a clear height more than five feet, of any garage or any accessory building must complete the Non Conversion Agreement form. In the Agreement the owner certifies that they acknowledge that they are constructing a building in a Special Flood Hazard Zone and that they will not modify or convert the enclosure below the base flood elevation for any use other than limited storage or parking. This Agreement must be submitted prior to approval of the Rough-In Inspection. It will be retained as part of the permanent Building Permit record and filed with the Beaufort County Register of Deeds.
Manufactured homes have the same elevation and construction requirements as other new buildings when they are placed in a Special Flood Hazard Area. Recreational vehicles are allowed in Special Flood Hazard Areas without elevation requirements if they are fully licensed and highway ready at all times.