Pre remodel plumbing question

[skylarkguy]

Ok, first post says galvanized and the second says cast iron- minor difference in the big picture but it helps me understand. I’m guessing the “rat” is the remodel. The 4” line could have been an old vertical stack that was later abandon in favor of the other vents- this probably occurred with the remodel.
With all those other vents on the roof this vent can’t be serving that much. Verify it’s not serving over 24 fixture units- that’s like 3 full bathrooms, a kitchen and laundry. Just google “plumbing fixture units” if you want to verify the numbers for each fixture. If it’s not over 24 units, cut the cast/galvanized pipe down in the crawl and run a 2” line to the roof from there. Since you have already done roofing I’d switch the roof jack to a 2” as well-going back to 4” isn’t code.
ABS or PVC is fine- I like ABS. Use the correct fittings- 4” no-hub coupling, little piece of 4” ABS, 4” ABS coupling, 4x2 ABS bushing reducer and away you go with the 2” ABS.

As a technicality- I believe your area is using UPC instead of IRC. They have a few differences regarding fixture units. They also have differences with AEVs and island vents. Some of that stuff is hard to change for the inspector.

Yep I mis-typed in the first post...the pipe is cast. I'm thinking i will replace with 4 inch where needed and do all venting with 2 inch. Those no hub couplings are pretty slick...I've used them before. Thanks for the advice.

 

[skylarkguy]

This is a new, old school tactic used by architects/contractors with an eye for aesthetics

My house is no architectural marvel...so I'll take any aesthetic improvement I can get.

 

[radioman]

I seen huge 4 inch inside diameter cast iron venting in city of Rochester when i was replacing roof on older homes. So there are no rats here. That being said.. Thinking about what op said.. I beleive if seperate multiple vents joined in the attic into the cast irpn pipe.. He should be fine. The number of angles shouldn't matter much as long its part of dry vent and minmize thw turns of wet vents. Be sure you read up on the type of elbows to be used for dry and wet vents. There is a reason for this and juat follow the guidelines will keep you trouble free with your drains and venting. With op asking questions if he can use mulitple lunes just tells me he is not familiar with plumbing venting and its pretty important. Terms like short elbows, sweeping elbows ,wye vs t's, direction of the sweeps for water and vents, etc all should be read up on before attempting the remodel. I strongly suggest a mockup before glueing and call in the town inspector or plumber and take a look. Yes permits cost money and plumber cost money but well worth it. It just ensures u doing it right and if they have auggestions just gladly change it and it will juat simply pass with flying colors. I treat all my remodels this way for my customers . i pretty much tell them we ahould pull permits becuase it protects them but really.. If i overlooked something or they have suggestion it just prevents a callback for me. Things and codes is continuously changing and i cant keep on top of it all. Heck .. Some towns are so lax it just scares me.