How to Seal Vent Flashing
If the flashing around your vent (called a flange) is old or failing for any reason, you will need access to the area of your roof beneath it. This is a bit of a task, so read it thoroughly before you begin, because it will involve both removing and replacing shingles and may prove tedious enough that you'll want to hire someone to do it for you.
||First you'll need to remove the shingles that cover your vent flashing's flange. To remove shingles, use a shingle ripper or hacksaw to cut any nails holding them in place and remove them. If any are damaged, it is a good time to replace them with new ones. Then cut the nails anchoring the vent flange and lift it off.
||Place the new flashing and flange over the vent pipe and secure with galvanized screws (or galvanized nails, which are not as secure but will be easier to install). Place the anchors to the outside so that they will be covered when you replace the shingles.
||Replace the shingles, making sure to cover any nail and/or screw heads with roofing cement. Place a generous bead of cement around the top of the flashing where it meets the vent pipe.
||Talk about your vent flashing to other DIYers in our Roofing forums; you can share tips or ask questions.