Hello again, I am wondering if I can run a 2 inch vent into existing 1 and 1/2 inch vent or do I need to run 2 inch all the way to the roof? Grandfathering ???

Grandfathered or not do what makes your system work best.
Certainly don't want issues with drains later
if there is a toilet on this line then that means 2" by code.

what I have is a toilet and a bath sink to vent into the kitchen sink vent of 1 and 1/2 Kosher?

Whether it is "Kosher" or not depends on your local plumbing code. However, it will work regardless of the code.

ask your local inspector. you never know....

You can but I doubt it would pass inspection.

Toilet needs to have a 2" vent. Vent cannot be reduced in size.

You can run 1 1/2 into a 2 but not the other way around.

Can you make the sink vent 2"? What s the size of the sink drain?
Like other said, local code vary.

well the inspector said it has to be a 2 inch vent so I am gonna go up and through a closet and then up through the attic to the rooftop. My only question is does it matter how many bends I can throw in there to get it to work or is there some code about that too??? Thanks for the input



Edited 1 times.

always best to check with the inspector if you don't know the code.
you don't want to get the pipe in and fail inspection.

You can use as many bends as you need to, just keep the vent sloping upward at all times.

Its air, a gas, not water or waste, so no limitation.

Most if not all inspectors would made you bring it up to code (2" thru the roof.