On the first day of hurricane season, a flood insurance requirement has become unavailable after federal lawmakers failed to extend it for a fourth time in recent months.

The National Flood Insurance Program, which is available to homeowners in some flood-prone areas, expired at the end of May after Congress temporarily renewed it in April. The lapse creates at least an eight-day window during which some buyers won't be able to purchase their homes, causing them to delay their closings.

Some mortgage companies require flood insurance. And for homeowners who live in federally designated flood zones, the federal insurance program is their only option.

Most homeowners in that flood zone rely on the federally provided insurance, said Ryan Castle, who oversees government affairs for the Charleston Trident Association of Realtors. He and other people familiar with the issue said they believe the program will be extended again soon, but the holdup creates a hassle.

"We're talking about the economy here," Castle said. "Buying and selling real estate is one of the things that keeps the economy moving, and that's not happening when closings are delayed."

Homeowners who already have flood insurance through the program are not affected.

Congress will have to renew the program in order for homeowners to be able to buy new policies. House representatives extended it until Dec. 31, but Senate leaders left last week for a week-long holiday break without authorizing an extension.

Congress returns on Monday.

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It's unclear how many local home sales are affected by the expiration. In March, the Charleston Trident Association of Realtors estimated that 40 percent of home listings were situated in a flood zone.

But some homeowners have been able to avoid the problem, said Patty Scarafile, chief executive of Carolina One Real Estate. She said most of her agents were able to either sign up for the insurance early or transfer the existing homeowner's insurance over to the new owners.

"One way or the other … we don't think many people will be delayed in closing," she said.

Reach Katy Stech at kstech@postandcourier.com or 937-5549.