Installing vents with roofs covered in metal roof flashing is actually much easier than you might imagine. All plumbing systems need to be vented to work properly. Venting opens the system up to air and also helps to get rid of noxious gasses. When installing these systems it's essential that you replace the flashing properly so that your roof is fully watertight.
Step 1 - Prepare
Make sure that you purchase any materials and equipment that you don't already have. When buying replacement flashing to install the plumbing vent you should ensure that this is the same type as the flashing on your roof at the moment. This will make sure that it fits properly and ties into the roof.
Step 2 - Remove Shingles
Remove the shingles from the immediate area around where you want to fit the vent. This is necessary to access the flashing which will be laid underneath the shingles. There may or may not be flashing on the area of roof you are working on, but it always pays to take a look.
Be gentle when lifting shingles so that you break as few as possible. Use a pry bar to prize these up off the roof. If you do break any then you will need to replace these later on.
Step 3 - Remove Flashing
The pry bar should be used again to remove the flashing, a block of wood can also be used to remove the flashing. Take care not to break any of the other shingles on your roof.
Step 4 - Fit the Vent Pipe
The plumbing vent pipe now needs to be fitted as normal. Cut a hole through your roof and fit it into place. Make sure that the hole through the roofing felt is as small as possible to minimize the chance of leaks.
The vent pipe should be fitted according to the manufacturer's instructions. Every house will be different and so you need to choose the best route for the pipe.
Step 5 - Add Flashing
Pull out any nails which are still in the roof, but take care not to dislodge the vent pipe. Now the piece of new flashing can be placed over the pipe and put into place. The flashing needs to be flat when installed and should be held in place using roofing nails.
Step 6 - Replace Shingles
Spread an even layer of roofing cement over the roof and flashing. Then bed the shingles down into this roofing cement. Lay the shingles on the roof and start fixing them from the bottom up. The shingles can be fixed using nails and the nail holes should be filled with roofing cement.
If you broke any of the shingles then you will need to replace these with new tiles, preferably of the same type and size as your current roof. This will ensure that they can be fitted easily and evenly.