A vaulted ceiling is a slanted wall, and is insulated similarly--by installing paper-backed fiberglass insulation between the wall studs before you drywall. The main difference is that the strips of insulation tend to fall as you're installing them, so you have to adjust your working method to prevent that.
Instructions
1. Measure one side of the vaulted ceiling from the top of its peak to the bottom where it meets the lower walls of the room.
2. Place a piece of scrap plywood or cardboard under the area of the floor on which you are going to cut the insulation. Roll out the fiberglass insulation on the floor, paper-side up; roll at least a foot more than your measurement.
3. Place your tape measure next to the strip of insulation and extend it to the measurement you took. Press a square across the width of the insulation at that measurement, and cut it with a razor knife. Compress the insulation with the square to get the knife through.
4. Take the cut piece up to the peak. Hold it between two of the studs, with the top end of the piece at the peak and the bottom hanging down. The bare side of the strip faces the ceiling, and the paper faces you. Staple through the paper to secure the piece to the sides of the studs.
5. Work your way down the strip of insulation, shooting staples into the studs every one to two feet. Set the piece entirely into the cavity formed by the studs.
6. Follow the same procedure to cut and hang fiberglass pieces between each pair of studs.
Tags: fiberglass insulation, peak bottom, piece peak, strip insulation, vaulted ceiling