Proper Venting Question

[gkull]

I'm having trouble fining a clear answer to the this question in the NSPC book...

After a toilet vent extends vertically up a wall cavity into the ceiling, is there a limit to how far that vent may extend horizontally before it reaches the vertical part of the main vent stack that extends to the roof? Also, is there a maximum number of bends allowed?

I know toilets require their vent to be no more than 6 feet away, which is not a problem for me to achieve in the piping under the toilet and in the wall next to the toilet. However, to avoid creating very problematic bump outs in the bedroom above this bathroom, I need the vent pipe to make a 90 degree turn in the joist bay above the bathroom, extend approximately 8.5 feet horizontally in that joist bay, and then make another 90 degree turn through the joists and extend another 8 feet to reach the main vent stack that extends to the roof. I attached a pic of my proposed schematic to hopefully make more sense of this question. The 3" pipes colored red are the ones in question. Are there any pros here who might be able to answer this question? Thanks in advance for any insight you might be able to provide!

 

[Twowaxhack]

If this is in a house I doubt you’d ever exceed vent length limits.

 

[Zanne]

There tend to be limits when it involves the part of the vent that is likely to fill with water. The whole point of the trap arm length is to prevent the pipe being completely blocked with water. So, you don't want your trap arm length to be so long that at 1/4" slope the water will block the trap weir. For vents that do not have water going through them, I don't know if there is any maximum length. I think that limit would be based on how much space you have to get the proper slope. I have never seen any rule about the horizontal runs of vents after the trap arm (aside from needing 1/4" per foot slope).

I'm no pro, but your drawing looks fine to me. You don't have to worry about bends so much because air flows easily.

Will these pipes be in an interior or exterior wall? There are building code rules on how many studs can be pierced on load-bearing walls, but I think that can be mitigated with support plates & sistering up studs. I can't remember the exact number. You will also have to make sure to add nail plates to each stud over where the pipes pass through and make sure they don't conflict with any other obstacles-- like ductwork or electrical.

 

[gkull]

Thanks very much for the replies. These pipes will be in the interior of the house. No load bearing walls will be pierced, but good point about the maximum holes in the joists. I'll check that. They're full 2.75" x 9" old growth timbers, but I'm sure there is a limit.

 

[Zanne]

Thanks very much for the replies. These pipes will be in the interior of the house. No load bearing walls will be pierced, but good point about the maximum holes in the joists. I'll check that. They're full 2.75" x 9" old growth timbers, but I'm sure there is a limit.

If you will be going over the limit you can reinforce to mitigate. If its not load bearing it really shouldn't be a problem, but nail plates and/or stud shoes will help. Stud shoes are designed to go around where the pipes go through the studs- they act as nail plates and reinforce the studs.