What's the deal with vent Sizing?
Posted by cris on July 03, 19100 at 10:21:33:

I was told that for my vents (stink pipes) that 1 must be 4" all the way through, and the other could be reduced down as far as 1/2 or 2". Right now it looks like have one thats a 3" all the way.. The other one from the basement up to floor level on 2nd floor is a 4". That's as far as I got with the project. Now I have 2 choices: 1) shim the wall out to hide the 4" pipe or 2) reduce down to a 3" which happens to fit perfectly and then at the attic ceiling go back to the 4" up and out. I was told that this is illegal, according to the Rules (code). What is the theory behind this, i.e. Why? I have an old plumbing book (1985) that shows diagrams with 3" pipe all over the place with several fixtures tied in. My house is 111 years old, I really need to use the 3" now, but I don't want to pose a danger to anyone? Is this safe?
