Renovating in a Hamptons flood zone: the 50% rule

In the Hamptons flood codes we reviewed, work costing 50% or more of a building's market value is substantial improvement, and the building must then meet current flood rules, including elevation to 2 feet above the base flood elevation. The Town of Southampton adds up improvements over 10 years. Flood barriers cannot be used to bring such a house into compliance.

The most expensive surprise in a Hamptons flood zone is a renovation that turns into a requirement to raise the house. It happens when the work, or the damage being repaired, crosses 50% of the building's value.

The 50% rule

In the flood codes of the Town of Southampton, the Village of Sag Harbor, the Village of Quogue and the Village of West Hampton Dunes, an improvement is "substantial" when its cost equals or exceeds 50% of the structure's market value, and damage is "substantial" when repairing it would cost that much (Southampton §169-4, Sag Harbor, Quogue, West Hampton Dunes). We did not find the definition in the East Hampton Town overlay article; ask the Building Department.

When a project is substantial, the whole building has to meet current flood rules. In these codes that means the lowest floor at 2 feet above the base flood elevation (the lowest structural member in V zones), and only parking, access or storage below it, with flood openings.

Southampton counts 10 years

The Town of Southampton's flood law, as amended through 2023 (Chapter 169, definitions), goes further:

• Cumulative improvement. Improvements are added up over 10 years, so a kitchen one year and an addition a few years later can together cross 50%.
• Repeat damage. Flood damage on two occasions in 10 years, averaging 25% or more of market value each time, counts as substantial damage.
• Coastal A Zone. Southampton treats the Coastal A Zone, where waves of 1.5 feet or more are expected, like a V zone for elevation.

This applies in the Town outside incorporated villages. Sag Harbor, Quogue and West Hampton Dunes count each project separately in their codes.

What the State code adds

New York requires 2 feet of freeboard statewide, and the 2025 Uniform Code applies to permit applications from December 31, 2025 (NY Department of State). The March 2025 draft residential code would add 18 inches for sea-level rise next to tidal water (draft R306). Confirm the required height for your permit with the building department.

Where barriers fit

• Not for compliance. FEMA says sealing may not be used to bring a substantially damaged or substantially improved house into compliance (FEMA, chapter 7), and these codes allow watertight floodproofing only for nonresidential buildings.
• For houses that stay as they are. If your project stays under the threshold, barriers on doors and garages can help against shallow water, within FEMA's 2 to 3 foot limit and away from waves. See DIY vs installed flood barriers.
• Things that count in any project. Flood openings in enclosures and raising equipment are required in new work and can lower NFIP premiums; see flood barriers and flood insurance.

Before you design

1. Get the elevation certificate and the flood zone for the lot.
2. Ask the building department for the building's market value basis and, in Southampton, the improvements already counted in the last 10 years.
3. Price the project against the 50% line before the design is final.
4. If the house will be raised, involve an architect who works with flood elevations from the start.

For the full rules by town and village, see flood protection for Hamptons homes.

Frequently asked questions

What is substantial improvement?

In the flood codes of Southampton, Sag Harbor, Quogue and West Hampton Dunes, it is reconstruction, addition or other improvement whose cost equals or exceeds 50% of the structure's market value. Substantial damage is damage that would cost 50% or more to repair. Either one means the building must meet current flood rules.

Does Southampton count past renovations?

Yes. Southampton's law, as amended through 2023, counts substantial improvement cumulatively over 10 years, so several smaller projects can add up to the 50% threshold.

Can I use flood barriers instead of raising the house?

Not to meet the rules. FEMA says sealing may not be used to bring a substantially damaged or substantially improved house into compliance, and the five codes we reviewed allow watertight floodproofing only for nonresidential buildings.

Who decides whether my project is substantial?

The local building department, which acts as the flood administrator under these codes. Ask before you design the project, not after.