Plan your installation: Measure interior position of skylight and mark. Drive nails from inside through the roof at four corners to locate the correct area from above.
Cut away the roof: Find exterior position of skylight and remove shingles to 2" away from the corner nails. Double check the dimensions and cut away the roof to the nail lines.
The roof curb: Build your roof curb ahead of time using 2" x 4" or 2" x 6" lumber to inside dimensions of roof opening. Apply sealant along bottom of curb and place.
Sill and step flashing: Form sill flashing and rest on shingles. Form step flashing beginning at bottom.
Install skylight: Now you are ready to install your skylight. Apply 1/2" thick bead of non hardening caulking on top of the roof curb. Set skylight firmly upon the curb. From interior, screw the skylight to the curb through the pre-drilled flange.