So soon I am going to be installing a standard 6ft French door in the back of my garage. The wall is unfinished so I am looking at the studs. The garage was built a number of years and owners ago and had a small garage door big enough for a riding lawn mower, it has since rotted so I removed it. My question is the original rough opening in the framing was 6ft wide, but the garage door was not that wide so they built it in, I tore it down to the original, but on the outside the hardiboard siding and molding go over the rough opening into the door way. Can I draw a line and use a circular saw to basically cut off about 2 inches Harbiboard and plywood underneath? Is that the proper way to do it or do I need to remove each piece and cut individually?