We added a new 1/2 bath the plumber installed an inside vent which I do not like.
Is this legale can it be vented to the other bath vent? How much will it cost to have it vented to the outside?

Hobert...

Was a plumbing permit pulled on the job? If it was I am sure that it is legal in your area to use an an air admittance valve (called a provent sometimes... see pictures). A plumbing permit is required for all bathroom remodels... including electric permit and sometimes, if job involves moving walls, etc. a building permit.

If permit not pulled, well then hard to say if a provent is legal in your area or not. You would need to call the local plumbing inspector to find out and that would mean that you would probably be fined (double cost of permit) and have to pull all appropriate permits.

Then you may or may not have to run a 2" vent from the bathroom to the attic where it can connect into a 2" vent up there or it can penetrate the roof by itself.

Hard to say on cost here without knowing distances and just how much wall and ceiling would have to be disturbed.

Let us know if need more info.

MARK

I don't think I understand what you mean by saying "....inside vent...".

In residential applications, all vents should be inside the wall. Yes, vents can be combined with other vents from other bathrooms. Yes, vent can be run independently all the way through the roof. Here, you have to cut the wall, and roof, to run the pipe. Than install flashing on the roof.

How much? It is hard to estimate. There are too many variables to estimate labor costs. But, it should be part of the "per fixture" cost original plumber charged you when roughing-in your 1/2 bath.