Roof Flashing for Bathroom Fans Video
First, if you are not comfortable working on the roof, do not attempt this project. Falls resulting in injuries or death are possible.
From inside the attic, locate the hole where the vent will go through the roof. It must be located between two roof joists. Once located, drive a large nail up through the roof from the attic. Once back on the roof, you can locate the center of the hole from the nail. There should not be any chimneys, other vents or other objects within two feet of the center of the hole.
Mark the hole on the shingles with any marker you can see on the roof shingles. Make the hole slightly larger then the diameter of the vent tube. Use a reciprocating saw to make the cut in the roof. You can cut right through the shingles at the same time you are cutting the roof sheathing.
Shingles are overlapped so the rain will run off the roof. The upper shingle is always on top of the lower one with part of the lower shingle underneath the one above it. The flashing on the bathroom fan vent works like a shingle. If it just laid on the roof, the flashing with be above all the shingles and the roof will leak. The top edge of the flashing has to go under some shingles.
To do this, some nails have to be removed from the shingles. The nails should be located directly above the slit in the shingle. Lift the shingle and located the nail. Use the flashing to determine which shingles are affected. Use a flat pry bar to remove the nail(s). If the part of the vent is not round, some of the shingles will have to be cut to match the vent. Put the flashing in the hole and outline the flashing edges. Cut the shingles so they are about 1/2" inside the edge of the flashing markings. A razor knife can be used to cut the shingles.
Once cut, slide the upper part of the bathroom fan vent flashing under the shingles at the top. The vent flashing will sit on top of the shingles on the down roof side. Nail the roof flashing in position. Apply caulk over any nail head that is not under a shingle. This will keep that nail hole from leaking.
Done properly, your roof vent will not leak.