Since sprawling, high­rise apartment buildings are relatively scarce in D.C., group houses are a common rental option and come with a unique set of leasing issues. A number of people sign a lease, in a group house, says Ann Marie Hay, director of the D.C. Law Students In Court Program, but then people sequence through the house. Some move out, new people move in ­­ and then some of the people who originally signed the lease are no longer there. Under a concept known as joint and several liability, if legal disputes arise or back rent is owed, the house`s landlord can pursue all the original signers of the lease for remedy, or he can just concentrate on the one or two left in the house.