roof pipe extension

[highway]

I just did a roof over and the vent pipe from the bathroom had a plastic vented cap over it. I needed to raise the vent 4" so I hope I did the right , I added a 1 1/2 collar and a piece of pipe and put the rubber boot around it..... is there a need for the plastic cap ?

[Greg]

Often the cap has a screen to keep bugs & critters out. Other than that there is no real functional reason for them.

Greg