Tiny houses are all the rage. They attract environmentalists, adventurers, and scrooges alike, by offering their owners sustainability, mobility, and debt-free living. But tiny homes are often illegal.

While new homes in the United States now average 2,600 square feet, tiny houses can be as small as 100 square feet. And they're gaining in popularity. Tiny houses are cropping up in urban alleyways in progressive communities like Portland, Seattle, and Washington, DC. In July 2014, the television show Tiny House Nation debuted on FYI. And the Tiny House Conference will hold its second annual meeting in April 2015.

Tiny solutions for large problems

The tiny house movement may be a countercultural trend, but it's more than just a fad. Tiny homes are popular because they offer entrepreneurial solutions to serious social problems.