Check out the photo below. Do you see the problem?
The white pipe sticking up out of the roof is a plumbing vent. The rubber boot at the base of the plumbing vent is part of the flashing kit for this vent, and the boot has dried out and split. Here’s another photo of a split rubber boot, taken from the same roof at a different location.
And here’s another one.
This is what happens to rubber boots over time. They seem to last about 10 – 15 years here in Minnesota. Here’s water damage at a bathroom ceiling, which resulted from this defect.
There are three ways of addressing this defect. The first is to replace the plumbing vent flashing entirely. This is the most labor-intensive option, so I can’t imagine anyone doing this.
The second is to slip a new rubber collar over the existing collar. You can find new collars at home improvement stores for under $10, and there are no tools needed for this repair.
It’s a simple product that can be easily installed in minutes and comes with a lifetime warranty. Home Depot sells them for around $25, which is a more expensive option than anything else, but well worth the price. They come in 1-½”, 2″, 3″, and 4″ sizes.