Venting question....

Forgive me if I ramble a bit on this one... I've seen alot of plumbing and lots of different methods and pretty much all work equally well. My idea for new construction is to install plumbing in such a way as what is best for the overall use and maintenance of the project and ideally maintenance free as well as ease of change, addition, and rennovation. The one question which has resulted from new construction is the final venting. I've seen vent circuits that start as a wye next to a cleanout in a basement and run two stories above that then out the roof with two 4" pipes. This appeared to be way overkill and resulted in serious roof leaks. The particular house I wondered about has a bath and laundry in the basement, kitchen and two baths on the main level and two full baths in a loft upstairs. The kitchen has a looped vent on it's 2" drain line which just goes up to about 42" then comes back down to a wye in the drain. All other fixtures are connected via 2" pipe to the 4" vent pipe from near the cleanout or the 4" main sewer stack. It's these two 4" pipes which run straight out the roof on separate sides of the house... can not locate photo's or I'd put them online. I guess that the question I'm asking is how you would terminate such venting? From everything I've seen it looks like one 2" pipe thru the roof would have sufficed very well and been much less destructive to the integrity of the roof. If I can locate the pics I'll post them.

You need to look at the code you are on, but under any code I don't think one 2" through the roof would come close to cutting it for the DFU's you describe. A single 4" would do it, and now we are just talking about the convenience ( or not) of joining vents stacks from opposite sides of the house together somewhere, for a single roof penetration.

Millions of homes are built each year with no leaks on the roof stack penetration, so whether you have one or two or three, they can be done reliably and if you have leaks, they were not done right.