Those who share housing have less of an impact on the planet than if they were all in seperate dwellings-each person's carbon footprint is smaller. Sharing Housing also allows for sharing:
Due to House-Mates sharing housing each person requires less stuff.
Sources: Sharing Housing: A Guidebook for Finding and Keeping Good Housemates
Contributors: Annamarie Pluhar
Recommended Books: Sharing Housing: A Guidebook for Finding and Keeping Good Housemates