[Alan]

Not sure what California code is, but Oregon requires the same cross sectional area to be going out through the roof as what the minimum required building drain is.

For example, if you have a 3" drain, Oregon would require you to have either :

1 3" vent
2 2" and 1 1-1/2" vent

or any other combination where the area of each meets or exceeds the area of the 3" drain.

If your fixture load requires a 3" drain and you have a 4" drain, then you still go by the surface area for a 3" drain.

 

[niecyt]

Thanks for your reply. I think what is going to happen is that the sink and toilet are joining together and going out the roof with a 4" vent. The shower is installed where the sink was so that vent will remain the same, it is some old cast iron job and think its 2" but can't swear, might be 2 1/2. I
just want to make sure stuff is done right on this job so that when I decide to sell I don't have to re-do everything since this area isn't the richest in town and most folks buying will be going FHA,,very picky about inspections!
Thank You