[patads]

I am building an addition that will increase the size of my kitchen and bath. My main waste line is not vented and is tied into a septic system. The house is 100 yrs. Old. My question is if I run a 3" pvc line of the main line and vent it straight out to the roof using 3" pvc pipe do I have to vent each fixture separately and tie into this vent or is the 3" stack adequate. there wil be a kitchen and bathroom sink, tub and toilet all with 10 feet of the 3" stack.

[massplumber2008]

Hi Patads:

You definitely want to have that three inch pipe penetrate the roof by itself.

Then you will need to run an individual 1.5" vent for the kitchen sink and will need to run a 2" vent from the lavatory to vent the lavatory and WET VENT the toilet and tub (depends on layout... may need to add another vent for the tub). Basically as this diagram below shows (study the waste vs the vent). This picture is not exactly how to do things.. but should give you an idea of how it goes.

All these vents can come together in the attic and should connect into the three inch vent pipe just before it penetrates the roof.

Hope that helped. Let me know what you think... MARK

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[speedball1]

if I run a 3" pvc line of the main line and vent it straight out to the roof using 3" pvc pipe do I have to vent each fixture separately and tie into this vent or is the 3" stack adequate.

Every fixture that has a trap will have its own vent or be wet vented. That said, Mark put up a great diagram, let me see if I can add a bit to it. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim. In my area a 3" vent's mandatory. We usually run it on the kitcken vent and continue on with a 3" drain to the 4" main. Good luck, Tom