So much of what is in our homes these days is factory-made — toasters, furniture, toys — but not the homes themselves.

Most are still built on-site, as opposed to being prefabricated and trucked in. That doesn’t make sense, says Sheri Koones, author of four books on prefab housing, including the new Prefabulous and Almost Off the Grid: Your Path to Building an Energy-Efficient Home (Abrams).

“Would you want your car to be built in your driveway?” asks Koones of Greenwich, Conn. “Of course you wouldn’t. You want your car made in a climate-controlled factory by skilled professionals on an assembly line. Wouldn’t you want the same thing for your home?”

Prefab housing, a concept that’s been around at least since Sears and other companies introduced mail-order kits in the early 1900s, generally refers to factory-built modular and panelized housing. They are built to the same code as traditionally built homes, with additional structural requirements to make sure they withstand being transported. Depending on the home’s size, multiple pieces (or modules) are delivered to a site and secured together onto the foundation in a matter of hours.

Prefab homes are typically 60 percent to 90 percent complete at the time of delivery, but often require an additional two or three weeks for finishing touches.

By contrast, mobile homes, which carry much of the stigma against prefabricated housing, are built to a more lenient federal code, arrive on their own wheels, depreciate quickly and are not generally zoned for urban use.

Because modular prefab homes are indistinguishable from site-built homes, they have become increasingly popular, pushed by the growing interest in green building.

“Prefab homes are much more efficient and environmentally friendly. There is so much less waste in the manufacturing process. Any excess materials can be recycled into other homes or sent back to the manufacturer instead of ending up in a dumpster,” Koones says. “Because the materials aren’t exposed to the elements, prefab houses avoid problems with mold, rot and bacteria… .”

She also cites worker health and safety as a benefit to building homes off-site. “Prefab construction professionals can work year-round, indoors, without being exposed to the elements.”

Still, some consumers remain unsure of what a green home built off-site would entail.

Greenfab, a Seattle company, recently used a newly built prefab home as a teaching tool. After producing the first platinum LEED-certified prefab home in Washington state, Greenfab opened the modern house to the public for three months. School groups, builders, buyers and nonprofit groups toured it.

“People in the neighborhood just saw a foundation in the morning, and came home to find a completed house,” says Johnny Hartsfield, founder and president of Greenfab. “Our main goal as a company is to educate the public on the benefits of green and prefab.”

He also lists cost as a reason to go prefab. Since the homes are pre-designed, he says, there are no architect fees, time delays or cost overruns.

“Site building is loud and stressful,” Hartsfield says. “We want to make building your home more exciting and fun — we don’t want you to hate it or get divorced over it.”