Vent pipe through the roof...

Quick question on the size of vent pipe I should run through my roof.

I have a basement bathroom with tub/shower, toilet, sink and bar sink. The bar sink has a grey water pump and there is an ejector pump. Pretty much everything is vented with 2" pipe, and all those go into a pre-existing 3" pipe that the builder had put in. This 3" pipe goes up 2 stories to the attic. Can I neck down the last 6 feet or so, to go through the roof with 2" pipe or should I stick with 3"?

Also, do I was planning on protruding through the roof about 12-18"...

So, 3" or 2" through the roof?

Thanks...Mike

I'd stay with 3" with that number of fixtures being vented. Check your building code though, or call your city/county inspector and ask to make sure!

you cannot reduce the vent, only increase. If you wanted it to be 2" then it needs to be 2" all the way. 12-18 inches sounds excessive. Depending on your local code it is usually less. UPC is 6" min but common practice here in hawaii is to vent thru the roof 10 inches.

In northern climates 18" through and 3" diameter is usually minimum.