Pro Tip 2
Depending on your roofing material and roof slope, there are different types of plumbing vent flashing that can be installed and NO – roofing cement is NOT one of them.
Plumbing vent flashing manufactured specifically for this application creates a waterproof / watertight seal around the roof-penetrating pipe without the use of any sealants. The most common types of materials used for this purpose are:
• neoprene rubber
• sheet metal with a neoprene rubber insert
There are also more sophisticated and expensive copper or galvanized steel plumbing vent flashing types assembled from two or more pieces. While serving the same purpose, they also add appeal to your house’s roof.
Neoprene rubber flashing and sheet metal with neoprene rubber types are very easy to install, but you have to keep in mind that water will penetrate it if you fail to do it right. The most common mistake is placing the flashing on top of the sloped roof surface material (shingles, rolled composition, metal, etc.) and applying roofing cement or caulking around it.
Top and side edges of the plumbing vent flashing apron (this section is mostly hidden under the roofing material) have to be inserted under the slope roof surface material with the bottom edge exposed. That open bottom edge prevents any possible condensation from the pipe sweating from being trapped under the roofing material, and can eventually cause roof decking damage or mold growth in the attic. Any other installation is un-professional and will most likely fail over time.
Although neoprene rubber has a long life span, it might eventually crack along the seam with a plumbing vent pipe, and at that point, I would definitely recommend replacement. If you’re able to pick a warm day for this procedure, it might be possible to slightly lift the top shingles (they will split / break if it’s cold and you will need to replace them) and replace the flashing without causing any damage. You can use a hacksaw blade to remove nails holding down shingles located above the plumbing vent stack and the vent stack flashing itself. Just slide the blade underneath the surface and cut any nail that prevents flashing removal.