reducing vent size

[straightjacket]

Remodeling a master bathroom. The old vanity covered the vent stack coming up through the floor out of the basement. The new vanity will not.

There's a joist almost directly under the base plate. I'm wondering if I can reduce the 3" vent down to 2" for a short run to get it through the base plate and the joist underneath. My plan is to drill a 3 1/4" hole in the base plate and the joist underneath. This should allow me to route a 2" pipe with an elbow attached. I'd then run the 2" back into the 3" main in the basement.

There are 4 pieces tied into this vent - toilet, shower, double vanity, and a utility sink.

Any problems or suggestions for my proposed idea?

[hj]

1. If you drill through the joist you might as well cut it off, because that is what the hole would do anway.
2. If that is a 2x4 wall a 3" fitting would be about 3 3/4" o.d., completely filling the cavity, and still project outside the stud, which does not appear to be the case in that picture.
3. I would opt for a different method, but would have to be there to see what is possible.

[straightjacket]

1. If you drill through the joist you might as well cut it off, because that is what the hole would do anway.
2. If that is a 2x4 wall a 3" fitting would be about 3 3/4" o.d., completely filling the cavity, and still project outside the stud, which does not appear to be the case in that picture.
3. I would opt for a different method, but would have to be there to see what is possible.

It's a 2x6 wall and the joists are 2x10.

Maybe this would be a better option...



I'll notch the 2x6 to the right (not load bearing) and run the 3" through that. This will now be behind the vanity. I'll cut another hole in the subfloor and run the 3" down into the basement and then elbow it back over to the left.

[MACPLUMB]

Yes; thats exactly to the way it should be done; you never ever put a reduction in the pipe the way you showed the first time!!!


JERRYMAC MASTERPLUMBER & MASTER DRAINMAN