Certainly depends on the family, but my family of 3 lives in 306 square feet and we love the simplicity of our home. I designed it and we built it ourselves in 10 weeks for $10k. It's solar powered, rain water catching and fully sustainable. It uses 1/2 a cord of wood for a average 18 degree winter. It's on 1 acre or 5 city lots and we'll be debt free in 10 years. the house should be paid off this year, leaving only a $403 monthly payment for the next 9 years
I'll be travelling by motorcycle once I get it paid off!