drywall over horsehair plaster
Hang horizontal on old framing. You'd be lucky if the layout works where a tapered edge breaks on a stud every time standing the board up. If it doesn't, you'll have a cut edge butting to a tapered edge and will have a harder time finishing. Use the longest sheets possible to minimize butt joints (which should be staggered). Start with a 2' rip at the top (cut edge to the ceiling) and the other two full sheets under that. Ceiling gets hung first. The 3 floors would come out to 4200 sq.ft. of living space, which would take somewhere in the neighborhood of 350 sheets of 12' board if you're doing the whole thing. Quite an undertaking for a DIY'er. Best of luck.....
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