The Zoning Board of Appeal on Tuesday unanimously approved a plan by the Gavin Foundation of South Boston to turn the former St. Gregory convent at 2200 Dorchester Ave. in Lower Mills into a 30-bed halfway house for women trying to recover from substance abuse.

Gavin CEO John McGahan said the exterior of the former convent building would remain the same; all the work would be done inside.

McGahan said women accepted into the program would spend four to six months as residents, with personalized treatment programs aimed at helping them deal with their substance abuse and gain skills to find jobs after they leave. He said the center would be staffed around the clock - with five full-time workers during the day, three in the evening and two overnight.

He said that although the program will accept women from Mass and Cass., they will come to Lower Mills only after completing medical detox and then a further clinical program first.

He said the program will be aimed at single women. However, women who are pregnant when they arrive will be allowed to stay with their child in the program for up to three months if they give birth while still a participant.

The mayor's office and City Councilors Frank Baker (Dorchester), Michael Flaherty (at large) and Ed Flynn (South Boston) and state Sen. Nick Collins supported the proposal.