Roof vent caps

Is there a size (diameter) of roof vent pipe that requires a (rain) cap?

Oftentimes a sink or toilet vent pipe will be 4" or more.

When does a roof vent pipe require a cap?


Attic vents need caps and plumbing vents do not.

Keep studying and it will all click.


Generally speaking, all roof penetrations need a cap EXCEPT plumbing. All plumbing vents (should) go to sewer/septic. Follow the vent pipe down… where does it go?

White PVC exhaust and supply for high efficiency boilers and furnaces don’t need them. The supply is usually turned downward though.