Home Plumbing: Multiple Waste Line Vents?

[5030tinkerer]

I am in the process of building a new home and noted that some homes have multiple roof penetrations for multiple waste line vents. Is there some reason/benefit for having more than one of these in lieu of just tying the various lines together in the attic or between floors? It would seem that the fewer roof penetrations you have, the better.

 

[beenthere]

Try to find the codes that control the limits of vents. It may be code, and it may be cost. I have three on a 1440 sqft home. They've never caused a problem in 38 years.

 

[AndyM]

I have only one in a 1840 square foot house, but all of my plumbing is along one wall of the house (but on two floors). All of the vents connect together in the atic before going through the one hole in the roof.

 

[plumboy]

Our code is to take out at least two 3" lines if you have 4" brought into the home,that would be for a home with 4 or more toilets.I go out 4 times on some smaller 1800 sqft 2 bath homes because of plumbing being so spread out and the vaulted cielings.Its alot easier/cheaper to go out with a $5 roof flashing than to make a bunch of turns and lengthy runs.I think it is better to go out mutiple times and keep the plumbing as short as possible.

 

[EddieWalker]

Code varies all over the place.

For more than one toilet, you need to have at least a 3 inch vent. If the other lines are close, you can add them to the three inch vent without any problems.

Eddie