The former St. Francis School on Saint Clare Road could be converted into an 18-unit apartment complex. On Tuesday, the Board of Appeals will hold a public hearing on a request for zoning relief filed by Waypoint Development LLC of Boston. Approval is needed because the apartments would be located in an area zoned for single-family housing. Relief from front, side, and rear setback requirements is also requested. The hearing will be held at 7 p.m. in Room 201 at City Hall.