Reinsurers Will Largely Be Writing the Checks to Pay for Irma Damage

Those carriers all are required to buy ample amounts of reinsurance to help ensure they have money for their policyholders, because they don't have the fat capital cushions of the national carriers. These reinsurance firms are specialty insurers that take on the risk of some of the policies sold by primary insurers. They send insurers money to help pay claims once claims reach contractual, designated levels.

As a result, the reinsurers "might end up holding the bag" for much of Irma's damage to residential properties, said Taoufik Gharib, a senior director at Standard & Poor's Global Ratings.

In addition to reinsurance, the U.S. government's National Flood Insurance Program will face payouts to those homeowners who hold its policies. Under standard homeowners contracts, insurers cover wind damage but exclude flooding. Much of Irma's damage is expected to come from storm surge.

The use of so much reinsurance introduces a few worries into the marketplace. The home insurers are exposed to potential disputes with their reinsurers over claims payments, industry analysts note. It also ties the home insurers' fates to the financial health of their reinsurers.

Irma's arrival is well-timed from one perspective: The global reinsurance industry is awash in capital. As of March, it had a record $605 billion capital cushion, which was built up thanks in large part to relatively few major natural disasters in the U.S. since 2005.