On a cross-country drive with his 11-year-old son in 2007 to install the first cabin in his new prefab building venture, Andrew Kelly passed a smallish log cabin. It was dingy, with a tar paper roof, asphalt creeping up to its porch and a soupy puddle wrapped like a moat along one side.

He posted a picture of it on a blog he’d started to chronicle the journey. He mockingly titled it, “My Competition.”

Five years later, the self-taught Miami industrial designer and his wife, furniture designer Gayle Zalduondo, are well on their way to establishing what could be Miami’s first successful eco-friendly prefab construction boutique, Cabin Fever.

They’ve completed 48 cabins already – including a ferry station in Homer, Alaska. Other projects under way include a San Diego campground and a Florida Panhandle communal housing development.

In the first six months of the year, the couple say they have racked up more than $1 million in revenue and sold about 20 small structures. The cabins range in size from 120 square feet to 800, and cost between $20,000 and $80,000. They can also be custom-designed for more space. Clients have used them for offices, guest quarters or even small homes. Several musicians have purchased them for backyard music studios, while one client Kelly described as an “off-the-grids, tear-up-the-credit card” type, installed a cabin in New Mexico. The place was so remote it didn’t have an address, just GPS coordinates.

Made from recycled steel that has “already been through several life cycles as cars or refrigerators,” the cabins are bright and airy, with maple veneer on the walls, exposed roof beams and clerestory windows. Those used for housing include an IKEA kitchen with butcher-block counters, a bathroom with a shower and a washer and dryer tucked in a closet.

And they can be built quickly. At last year’s International Contemporary Furniture Fair, where Kelly marketed his Zip cabin as a backyard structure, it took two workers just seven hours to erect one.

While originally designed to create extra space for existing homes, over the years they have transformed into single-family homes, an idea that Kelly continues to refine and one increasingly attractive to a new generation of homebuyers, said University of Miami architecture professor Rocco Ceo.

“People want energy efficient houses or cabins built in a way that’s more in tune with the environment in a lot of different ways,” Ceo said. “You can’t build out of pressure-treated (wood) and then have an organic garden next to it.”

As orders increased, Kelly added designs. He created the one-room Zip with its slanted roof and glass front, small enough, to “fly under the radar of permitting because of the size.” That first cabin, the Maxwell, with a curved roof and clerestory windows, can now be built large enough to accommodate two bedrooms and two baths.

And even though they are prefab, that does not preclude them from being personalized. Cabins built in Miami meet hurricane code while those in California can withstand earthquakes, Kelly and Zalduondo said. A mountain cabin might have more glass, to maximize the view, than an urban backyard cabin. Kelly designed another cabin for a Haiti project with a Dutch door, he said, so children could be kept in and animals kept out.