We want to convert the 6'9" x 8'4" sitting room off of the master bedroom in the 2nd story of our 1898 foursquare to a bathroom. We have all of the plumbing worked out, and have read on the forums that it's best to pull all of our plaster and lathe from the walls and ceilings. While we should be able to reinstall cement board and/or moisture resistant drywall on our ceiling and two interior walls, what do we need to do on the two exterior walls that were plaster directly over brick? Can we install drywall or cement board to the brick without studding them out using screws or glue? Do we have to put up stud walls on the exterior brick? If so, can we use wood smaller than 2x4s? Space is at a premium we don't want to reframe and retrim our 4.5' wide x 7' tall window on the 8'4" wall. The shower will be located in a corner of one exterior and interior wall, tiled floor to ceiling. And we'd like to tile the floor and all walls up to 5' high.