Hi,
I’m adding a bathroom in the back area of a house I’m renovating. The front portion of the house has a 6/12 pitch roof, but the back has a 3/12 shed type roof with rolled roofing. I plan to add the bathroom all the way back on the rear exterior wall where there is maybe 6 inches clearance in the ‘attic’. In planning for the waist pipe venting, I would like to avoid penetrating the low pitch roof and had two options in mind:
1. Run a vent pipe up to the ceiling, then follow the ceiling rafter to the main portion of the house and create a vent pipe through the roof there
2. Just use air admittance valves in the rear area.
This one wall will have a shower, lavatory and toilet on one side and a washing machine on the other side of the wall.
Am I mistaken in not wanting to penetrate the 3/12 roof? There is one penetration there already for a gas exhaust vent, but it comes out of the roof underneath the overhang of the roof of the main house, I was going to have it covered up, but possibly could use it as well.
Thanks in advance.
Jon
Replies
You can maybe use an AAV for a single sink, but for an entire bathroom I think it would be a bad idea, even if code does perchance permit it in your area.
Generally, you can run vent pipes horizontally (though slightly pitched for drainage) for a fairly long distance (not sure if there is any code limit). So you can run your vent to a place where a penetration is more to your liking, or even run it to join up with an existing vent.
Local code vary, so check yours before using an AAV. My state and local code only allow tehm in very few instances.
An AAV for your bath roomfor a full bath would need to be 3" minimum, so fitting it inside a standard 2x4 frame wall would be problematic, as 3" is the ID of the pipe. The OD of a 3" AAV is slightly over 4". It will fit in a 2x6 wall, but agian check with your AHJ.
If your current house stack is 4", I would just run to it and cut in a tee. I have run ventsas long as 30' to make a tie in and had them approved, but there is a limit on the number of elbows you can have in such a run (ICRC).
Another warning.
I have seen AAV's fail. A real pita to replace if they are burried in a wall.
Thanks much for the advice.
Since the distance from the exterior wall to the main house with the 6/12 pitched roof is only 12 feet, I think I'll just run it through the ceiling and up through that roof.
The main stack is cast iron and I don't want to try to tee into that, it's been there for many many years and surely does not want to be disturbed. :)