Use a hammer to bend the top edge of the soft lead roof jack down into the vent pipe.
What does a roof jack look like.
It might be something.
Also before you start installing your flashing you need to look to see if the wall in question has a corner on the roof face as in the image below.
You can usually feel sheathing nails which are driven into rafters through the underlayment attach a jack by driving two 16d nails never roofing nails into a rafter.
Cut roof shingles to fit around the roof jack and insert them under the existing shingles.
If you can see a dip curve or swag on the peak when standing in the street your roof has a problem.
If it doesn t have a corner and simply looks like the image below follow the second installation procedure.
Nail the new shingles down with roofing nails so the nails are covered by the shingle above.
What causes a sagging roof line.
Roof lines should be arrow straight.
Standard 2 by 10 inch lumber with fit into the channel on most roof jacks and should be available at any lumber yard.
Avoid using short pieces as the risk of a length of lumber tipping upward if you should happen to step onto the end of it is greatly increased.
Roof jacks provide a stable surface to work increasing safety and making it easier to apply roofing.