Replacing a vent pipe flashing on a worn out slate roof.

Written by Dennis Crookshanks

 We don't always get what we want.

Often in the roofing business we need to compromise on our idea of the perfect job to allow for
both economic concerns and design preferences of the homeowner. 

This was a small project in which a local contractor was remodeling an existing bathroom in a century home.

Old Lead Roof FlashingAll the existing cast iron plumbing for the bathroom was being replaced with new PVC, including the soil stack that ran through the roof.
The roofing is an old Pennsylvania soft gray slate that is near the end of its useful life but still keeping the water out of the house. The existing stack flashing is a piece of sheet lead cut to fit the pipe and nailed to the roof with galvanized nails through the shingles. It is sealed around the pipe by driving the lead into the bell housing at the roof line. I have seen more than a few vent pipes that come through the roof with an elbow and bell. Standard roof flashings will not work and you need to be creative to make a proper replacement. (Topic for a different post.)
Roofing tar was originally used to seal the lead flashing to the slate roofing. And more tar was added over the years as the old tar dried out, cracked and leaked.
In addition to the old flashing, the roofing slates with nail holes would also need to be replaced. There were also problems with the installation of a replacement aluminum gutter. Previous gutter installers had secured the new gutter by nailing the gutter straps through the eave course of slate roofing. Those slates would also need to be replaced.

The best option for us would have been to remove the existing slate, repair/replace damaged roof boards, install ice and water shield, drip edge etc. and install a new slate roof with copper flashings and a lead flashing for the pipe. An expensive option that was out of the question.
A good option for the owner would be to remove the old slate, replace/repair any damage etc. and install new asphalt shingles to match the main house. Not a bad idea as it would eliminate most maintenance for another 25 years, but, not what the owner wanted.



Even though it may have been close to half the cost of replacing the roof with new asphalt shingles, the homeowner wanted to keep the old slate roofing material for the looks, and just replace the stack flashing and repair the damaged slate shingles.
So be it.The remodeling contractor removed the old pipe and lead flashing and installed new PVC pipe through the roof. The contractor also supplied the aluminum and neoprene flashing as a lower cost alternative to a new lead full pipe flashing.
We simply removed and replaced the broken slate with matching salvaged slate, added a bit of new tarpaper, and installed the new flashing.

 

Depending on the amount of exposure to sun the neoprene flashing receives, it should last fifteen to twenty years before the collar will need to be replaced or re sealed. As long as there is no storm damage, or careless painters walking on the roof, or other incidents, the slate roof should also last another fifteen to twenty years. Maybe longer.

New aluminum stack flashing.