Greetings,
I am putting in a master bath and am looking for my best venting options.

I have read that all vents must go vertically until they get 6" above the flood rim of the fixture they are venting.
I have also read that, as far as codes are concerned, 45 degree drops can be considered as vertical. I am hoping this applies to vents below the flood rim as well.

I'd like to vent off my 2" shower drain using a 2" combo wve set at a 45 degree angle. This will take me over a few inches, to where I am below the wall, where I will use a 2" 45 elbow to take me straight up through the wall.

Any problems with doing it this way? I've included a birds eye view drawing of the bathroom DWV system. Any thoughts on better or different ways to do this would be appreciated.

the toilet doesn't need a seperate vent as long as it is within a certain distance from the lav drain and vent. keep the lav drain and vent 2 inch. the distance the toilet can be from the lav varies by different codes. it is at least 6-7 or even 8 feet.
as for the shower, the code doesn't say it needs to run 'vertical', it says it can not run 'horizontal'.
45 degrees or greater is not considered 'horizontal'..
just curious.. are you running the toilet drain thru all those joists?
it might save some work to put the 3 inch long sweep in the same bay as the toilet, use a 3 x 2 "Y" for the lav. it can run off the 3 inch at a slight pitch because even though it is a vent for the toilet it is washed by the lav drain. again, a classic wet vent.

Thanks Packy for explaining the codes on horizontal vs vertical vents more clearly. I'm happy that will work for the shower.

Yes, I will have to run the drain through all those joists. They are 14" wood I-joists, which, according to the manufacturers literature, are good to go for a hole that size. This section of the joists is also a much shorter span than the joists are rated for. However, I will have to drill a hole through the exterior band board to get the pipe in there all in one piece, from the outside. Hopefully I can reuse the piece I drill out, reattach it from inside with a 2x4 and seal from the outside.



Edited 1 times.

making a hole from outside and sliding in a length is always a good idea.
been there-done that..

"it might save some work to put the 3 inch long sweep in the same bay as the toilet, use a 3 x 2 "Y" for the lav. it can run off the 3 inch at a slight pitch because even though it is a vent for the toilet it is washed by the lav drain. again, a classic wet vent."

I have been thinking about this and want to make sure I understand the logic. Normally horizontal venting (less than 45 degrees) below the flood rim is against code, but it is ok if the horizontal portion is washed by another fixture ( and goes vertical within the critical distance from the trap). The idea being that a dry vent that is horizontal might be plugged by waste over time and cease to function well as a vent. However, wet horizontal vents are ok because the washing would keep the vent from plugging with waste. Am I understanding this correctly?

Yes, you are correct.