[rehabob]

We are adding a half bath to the first floor. Lavatory drain is 1.5" and toilet drain is 3". (See attached drawing) Should I connect a vent line directly from the toilet drain to the lavatory vent in the ceiling (red line in the drawing)? If this configuration is acceptable, what size should it be? My second option is to connect the lavatory drain into the toilet drain. If this is acceptable, can I use the lavatory vent as a 'wet vent'? I prefer to use option 1 because option 2 requires drilling holes through floor joists to connect the drain lines. Any suggestions would be appreciated.....Thanks in advance
Location: OH

 

[TheEplumber]

You can connect the 1.5" lav vent to the toilet vent at 42" above finish floor if you want, don't need to go to the ceiling. Also, the toilet vent should be 2" not 1.5". Once you tie the lav vent in it can still be 2" all the way to the vent stack.
Also, the lav can tie into the 3" anywhere downstream of the wc vent, doesn't have to be on the vert. as you show it.

 

[rehabob]

I've tried to decipher the Building Code on this question and gave up. Thanks for complete & informative answer!:thumbup:

 

[TheEplumber]

glad to help! Just remember that codes vary across the country. But I think you're good to go:thumbsup:

 

[Alan]

Just for ease of use as far as height of your vent travelling horizontally, we drill our holes at 50-1/2 " off the bottom plate to the center of our holes. That puts them above where the electrical boxes need to go so that they are out of the electricians way.

I'm very impressed with your drawing, by the way. Much easier to give advice when someone makes a complete sketch like that. Good work. I hope your project turns out as meticulous as your drawing did.

:thumbsup: