I am remodeling a home and we have 3 bathrooms in it. Two full baths and one 3/4 bath. The old plumbing system had one 3" vent and one 2" vent. We are changing the layout of the home a little bit and want to make sure we vent it properly. Does each toilet have to have a 3" vent sticking out of the roof? Can you get by running 2" vent up through the walls and then joining it to the 3" stack? Can you run two toilets to the same 3" vent stack? Thanks in advance for any feedback.

Do some study on wet venting.

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Does each toilet have to have a 3" vent sticking out of the roof?

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No, On our new construction we install one 3" main vent. Usually the kitchen vent.

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Can you get by running 2" vent up through the walls and then joining it to the 3" stack?

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Yes, this is called "reventing".

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Can you run two toilets to the same 3" vent stack?

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Unless local codes mandate a vent for each fixture you can follow Dougs advice and install a typical bathroom rough in using a wet vent. Let me show you how we install bathrooms in my area. 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. Good luck, Tom