The sunset streamed through the warehouse windows where René Píerre carved float props out of Styrofoam, carefully adding details to dozens of decorations for this year’s Mardi Gras celebration on Tuesday.

Mr. Píerre owns Crescent City Artists and has worked as a Mardi Gras float artist for 34 years. But he needed to figure out a new way of doing things this time. Parades were canceled by the city to prevent large crowds from gathering, so he and other celebrants decided to build floats in front of people’s houses instead.

It was mid-January, and with just weeks to go before the celebration, Mr. Píerre’s clothes and hands were covered in paint. Two float artists he mentors and a veteran float carpenter worked alongside him. “I’m running on fumes now,” Mr. Pierre said.

Mr. Píerre wasn’t sure the celebration would happen at all.

As the coronavirus spread, tourism was one of the first activities to disappear. That is no more evident than during the Mardi Gras season, which typically brings in millions of dollars to New Orleans starting every year.

The loss of parades is both financial and spiritual. Since the first Mardi Gras in New Orleans in 1857, elaborate floats have paraded through the city on the last Tuesday before Lent. Thousands of people fill the streets, and marching bands and dance teams come from all over to perform, their horns and drums echoing off buildings. Social clubs and groups of artists and organizers — that go by names like the Krewe of Orpheus and Krewe of Muses — spend practically every month of the year preparing floats and celebrations.

But not this time. Marching bands will not march. Bars throughout the city are closed. When parades were canceled, dozens of float artists and carpenters were laid off.

But the city was not ready to give up. Soon after the cancellation was announced, one woman, Megan Boudreaux, said on Twitter: “It’s decided. We’re doing this. Turn your house into a float and throw all the beads from your attic at your neighbors walking by.”

The idea took off, and krewes like Muses and Red Beans began working on homes almost immediately.

Ms. Boudreaux formed the Krewe of House Floats, which is keeping track of the number of installations that they and others have been building around town. There are roughly 3,000 house floats in the greater New Orleans area.