The FEMA 50% rule is a minimum requirement for participation in the NFIP. It limits the cost of improvements (additions, alterations, and/or repairs) to non-conforming structures to less than 50% of the “market value” of structure prior to the start of work.

On Sanibel Island, Florida—renowned as the "Shelling Capital of the World"—the 50/50 rule is the standard advice for cleaning and preserving the treasures you find on the beach. After a day of "Sanibel Stooping," you should soak your shells in a 50/50 solution of water and bleach for several hours or overnight. This solution is effective at removing algae, debris, and the "ocean smell" without damaging the shell's structural integrity. For sand dollars, a shorter soak of about 5–10 minutes in the 50/50 solution is recommended to turn them white, followed by a thorough rinse; soaking them for too long can cause them to become brittle and crumble. After bleaching, many collectors apply a light coat of baby oil or mineral oil to restore the shell's natural shine. A vital legal companion to this rule: never take "live" shells. It is strictly illegal on Sanibel and Captiva islands to remove any shell that still contains a living organism, including sea stars and sand dollars. Always check the "underside" for movement before placing a find in your bucket.