. >> reporter: lisa berkman, a professor of public policy and epidemiology at harvard university says that cohousing harkens back to the kinds of communities that used to naturally dominate our societies. >> you know, when you think about the apartment buildings that were designed at the turn of the century, they were designed as two-family houses or three-family houses, each on a floor. and those enabled multi- generation households to live together and still have their own housing. >> reporter: berkman says that cohousing can reduce social isolation and the detrimental health effects associated with it. >> social isolation relates to the number of ties and the quality of relationships that you have: religious ties, community ties, work ties. people who are very isolated, who are disconnected, have a mortality rate that's about three times as high that is, they're about three times as likely to die over maybe a decade, as people who have many, many more ties. >> reporter: 70-year-old jytte helle has lived in saettedammen for 30 years. >> it's important to me to be with a mixed group,