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"?