Skip to main content

Making Substantial Improvements (SI) Determinations

Information about making Substantial Improvement Determinations for Proposed Development in the Special Flood Hazard Area

Before improvements to buildings located in the Special Flood Hazard Area on FEMA flood maps can be performed, NFIP communities must determine if the building has been Substantially Improved. This is a formal determination of whether the cost of repairs and improvements will equal or exceed 50% of the market value of the structure before the improvement.

If proposed improvements are determined to be a Substantial Improvement (SI), the building must meet the same requirements in the community’s floodplain ordinance that apply for new construction. Communities may choose to adopt a higher standard (e.g., using a lower percentage to make the SI determination or adopting a cumulative SI provision) to further improve flood resilience in the community.

There are exceptions to the SI provision that apply for alterations of designated historic structures and corrections of existing code violations, as outlined in the community’s floodplain ordinance.

SI Resources

SI Determination Process for Community Officials

The steps that must be performed by communities to make an SI determination include the following.

Community Officials SI Determination Process Step

Step Resources
1. Review permit application to check if a Substantial Improvement determination needs to be made.
2. Verify the cost of improvements to the structure.
3. Verify the market value of the structure.
4. Make the SI determination and issue it to the property owner.
5. Permit development/ensure compliance with community ordinance.
6. Maintain documentation.