Vent Terminal Size

[Seaneys]

Hello,

I live near Chicago and am subject to the Illinois Plumbing Code

For some reason, I thought that I needed to expand to a 4" vent terminal poking through my roof. Section 890.1440 of the Illinois Plumbing Code says that I only need a 3" vent terminal.

I have two vent terminals covering about 3.5 baths. Is there something I am missing? I was thinking it would be a good idea to do the roof work before the snow hits tomorrow.


Any ideas why I thought I needed to jump to 4"?

Thanks,
Steve

 

[hj]

vent

The Chicago code used to require a one size increase with 4" minimum. The purpose of the increaser is to minimize the possibility of closure due to hoarfrost. A 4" increaser is almost twice the size of a 3" one so it would give a greater degree of protection.