Are Tiny Houses Legal?

The closing lines of Thomas Wolfe's, "You Can't Go Home Again" speak to the tiny house movement in a profound way.  

"Something has spoken to me in the night...... and told me I shall die, I know not where. Saying: (Death is) to lose the earth you know; for greater knowing; to love the life you have, for greater life; to leave the friends you loved, for greater loving; to find a land more kind than home, more large than earth.'"

When we depart from the norm to forge a new path we leave the familiar for the sake of discovery.  In the search for a new way of living, one of the questions often asked by aspiring tiny house dwellers is: Are Tiny Houses Legal?