[pment]

I am completing an upstairs addition in Houston, Texas, that includes a toilet, shower, sink, and a bar sink. The drain lines were previously installed. It consists of a 3" stack to the 2nd floor. There is then a horizontal 3" line that has the toilet, then the sink, and then the bar sink. A 1-1/2" line connects the shower to the fitting at the junction of the 3" horizontal and vertical line. The shower trap is 2' from the stack. The toilet flange is 5' from the stack. The sink is 8' from the stack. The bar sink is 15' from the stack.

There is an existing 1-1/2" vent thru the roof for a half bath (toilet & sink) on the first floor directly below this bathroom. It is at the extreme end away from the septic system of the existing drain system on the first floor.

When I continue the stack up to the roof, are the toilet & shower close enough that they don't require an additional vent line? I plan on connecting the two 1-1/2" sink vents to that stack also.

If I decided to use the existing location of the vent thru the roof for the new stack vent and tie that old 1-1/2" vent into the stack vent in the attic, what is the smallest size I can make the stack vent? Can it be 1-1/2" since the drain on the first floor at that location is probably still 3" and the vent would be half the drain size?

 

[TheEplumber]

How about a drawing? I'm a little confused

 

[pment]

The red pipes in the attached picture are what I need to add. I want to find out if I can use all 1-1/2" for the vents or do some need to be 2". Using 1-1/2" means I don't have to get on the 14/12 pitch roof.

 

[plumber666]

My Codebook's in the truck, and it's Canadian anyways, but it'll definitely work. You seem to have a pretty good handle on what you're doing. Be sure at the top of the stack by the shower, to extend the vent height to min. 42" before you run it horizontal.

 

[pment]

Can the 3 horizontal lines shown in red be truely horizontal or do they need to have any slope? I now know to move the lower of the 3 lines up to 42" above the floor.

 

[plumber666]

Can the 3 horizontal lines shown in red be truely horizontal or do they need to have any slope? I now know to move the lower of the 3 lines up to 42" above the floor.

A vent should have a small amount of grade so moisture, condensation will drain back towards the drainage pipes. Depending on where you live and what code you follow, this amount of grade varies greatly. A 1/16th or 1/8th inch per foot is plenty in my books.