From the side of the house measure from the corner along the wall 12 inches (30. 5 cm) and mark the spot with a pencil. Make sure that this line is level using the bubble on your level. Then use a tape measure to measure the distance between the mark and the underside of the roof. Your roof ratio will be this vertical length divided by 12 (for 12 inches). Some skylights are also designed specifically for use on corrugated metal roofs.
If there is anything in the way, it is usually easier to simply choose a new place for the skylight. Otherwise, it is possible to re-route plumbing and wires around the location. The opening should fit in between 2 rafters to prevent structural damage. If you are installing a skylight on a corrugated metal roof then it should be positioned just below the lap of the roofing and aligned with the grooves on the skylight fins.
Remove any drywall and insulation you cut through.
Be careful not to put weight on the cutout. These roof cuts are not reversible so make sure they are accurate. If making cuts on a corrugated metal roof you will need a special blade to cut metal.
To attach the sheathing for frame in place skylights, nail it down around the perimeter of the opening on top of the roof. [4] X Expert Source Ryaan TuttleHome Improvement Specialist Expert Interview. 24 September 2021. Then attach a strip of self-adhesive membrane along the bottom edge of the opening. One inch (2. 5 cm) of this adhesive should be folded over the edge into the opening of the roof. To create the curb for curb-mounted skylights you must measure the sides of the opening and cut four 2x6s (5 cm by 15 cm) to fit along the upper edges. Nail the four pieces together into the shape of a rectangle. Make sure this box is square and then toenail it into place around the roof opening. Toenailing involves driving the nails in at an angle to securely attach the curb to the roof. [5] X Research source
Be careful when working with the skylight at this point so that you do not damage it.
Skylights for corrugated metal must be slid under the upper flap of the roof. To slide it under the top flap of roof you will need to make two cuts in the roofing so that the skylight can be slid into location. This protects the roof from water leakage.
Skylights in corrugated metal roofs will be secured with 1 ¼ inch (31 mm) self-tapping sheet metal screws at 3 inch (7. 5 cm) intervals.
Start at the bottom edge when applying the membrane. Allow the ends of the membrane to extend past the corners. Then cut the membrane at a 45 degree angle from both corners to create two points. Secure the bottom point to the roof and the top point around the corner of the skylight frame. After applying the membrane on the bottom, put it on the sides and then last on the top edge of the skylight. Skylights in corrugated roofs should be sealed using roofing-grade silicone sealant. Apply a generous amount of sealant around the opening 1 inch (2. 5 cm) from the edges. [6] X Research source
The bottom sill flashing for skylights with a frame in place will be nailed directly to the roof at the top outside corners of the sill. The flashing of curb-mounted skylights will never be nailed to the roof. These flashings should only be nailed to the sides of the curb.
For the next piece, overlap the next step flashing piece on top of the shingle, again securing with a nail on the top outside corner. Place another shingle on top of that step flashing piece. Continue alternating step flashing pieces and shingles on both sides of the skylight.
The counterflashing should simply snap into place. Counter-flashing is essential for protecting against wind-blown rain and snow.
You will likely need to cut the ends at an angle to fit securely against the ceiling and roof surfaces.
Again use 2x4s (5 x 10 cm) to create these beams and nail them into place.
