The Web site for the City of Moore, Okla., recommends “that every residence have a storm safe room or an underground cellar.” It says below-ground shelters are the best protection against tornadoes.

But no local ordinance or building code requires such shelters, either in houses, schools or businesses, and only about 10 percent of homes in Moore have them.

Nor does the rest of Oklahoma, one of the states in the storm belt called Tornado Alley, require them — despite the annual onslaught of deadly and destructive twisters like the one on Monday, which killed at least 24 people, injured hundreds and eliminated entire neighborhoods.

It is a familiar story, as well, in places like Joplin, Mo., and across the Great Plains and in the Deep South, where tornadoes are a seasonal threat but government regulation rankles.