New plumbing vent question

[Bogucki]

Can I vent fixtures where they meet, or just before where their arm meets the main drain line?

Due to existing roof penetrations and stacks, it would be much easier to vent these fixtures on the top side of bathroom rather than on bottom side and running vent lines all the way around the bathroom back towards the top wall.

 

[Caduceus]

I deleted my previous post because I may have misinterpreted your drawing and description of how you want to do the installation.
Looking at it in two dimensions it looks like you want to run the vents off of the main for the fixtures unless what we are really looking at are the vents above the main and going through the walls?

 

[Bogucki]

This bath is on a second floor and I'm trying to tap into the existing roof penetrations. The wall behind the toilet is attic space, so I'm running the main drain right behind this wall in the attic. Normally I would vent the vanity and tub on their own wall, but in this situation I would have to bring the vents all the way around the tub and back towards the stack on the far left. If I can vent these fixtures behind the toilet side wall, it will make my vent runs about 8' rather than 20'.

The drawing is oriented as if you were laying on the ceiling looking down. Floor joists run parallel to drains and tub, terminating at the top wall so that I can run drain pipe right along the outside of this wall, in attic space.

 

[johnjh2o]

The way you have it drawn the vents for the tub and lav. are too far from the fixture.

 

[Bogucki]

How about venting here between the floor joists, closer to the traps?

 

[johnjh2o]

A horizontal vent must be 6" above the flood rim of the fixture. That would be 42" above the floor.

 

[Bogucki]

Thanks John,

So a lav that is 36" above the floor would require a vent to be 6" above the flood rim before turning horizontally; making the vent turn at a minimum 42" above the floor. That definitely kills my hope of venting close to the attic side wall.

I guess that means I will have to vent each fixture in the wall they are on, meaning I will have to run the vents all the way back around the bathroom.

So I'll bring the lav vent up the wall 42" before turning across and then tie tub vent with it, then take that all the way around the bathroom walls and take it out a roof jack. Does that look proper? My major concern with this run is making sure I maintain .25" slope from end to end with no dips.

 

[johnjh2o]

You got it. But to make it easier why not put the head of the tub and the sink on the same wall as the toilet.

 

[Bogucki]

Yes sir, I wish I could. The problem is that this bathroom has a sloped ceiling. It is part of a 1940's attic that was converted to living space many years ago.

The back wall is about 4' high, enough to accommodate a toilet and the back portion of the shower, but not tall enough to support a mirror/lav and shower head. The bottom wall, where the shower head and lav are going, is the stairwell wall and almost directly above it is the ridgeboard of the house, so I want to avoid making another roof penetration this high up the roof, although it would be much easier.

Preceding this, I had to rebuild the entire second floor since they utilized the original first floor 2x4 ceiling joists as floor joists for the second floor. I'm actually amazed how much wood will deflect before completely failing. This is what we found when we tore out dinning room ceiling; we knew we'd had no choice but to tear it all out and start over. And yes, those are scabbed 2x4's spanning over 12' supporting a bedroom.!

 

[uplumb]

It never ceases to amaze me what some people will do..

 

[plumber78]

I am not sure if air admittance valves are legal in your area but this is an example of how we would plumb it in this situation in most areas of ohio. While AAV's have been abused they do have their place. Just be aware that they can fail over time. In the diagram, I am using an AAV under the lav to wet vent the tub and then installing a relief vent where it goes under the opposite wall. The toilet would have it's own individual vent. I hope that I am understanding correctly what you are trying to do.

 

[Bogucki]

That would definitely be easier, I'm just not familiar working with them.

 

[johnjh2o]

There would have to be access to the AAV.

 

[Bogucki]

I understand John, that it would be exposed under the sink above the p-trap.

For some reason I feel like there's a stigma with AAV's, and that they are frowned upon using.

 

[plumber78]

They are frowned upon because there are some badly designed AAV's out there. There also some very badly designed plumbing systems out there to using nothing but AAV's and not even having one vent through the roof. AAV's are great for preventing a trap from syphoning. They allow air to be pulled in and then close keeping sewer gases trapped inside. As a result of this design, they do nothing about positive pressure and can cause problems if proper relief venting is not applied. They should not be used on anything that is pumped either, i.e., washer, sewage ejectors. Following those guide lines and keep in mind that you may have to change it in the future when it fails and they can be very useful.

 

[plumber78]

Studor and Oatey both make a decent AAV.

 

[Bogucki]

Yes, common sense told me that an AAV will do nothing to combat positive pressure. But then I thought, it would take a heck of a large and sudden pressurization of the waste lines in order to blow out the 2 existing vent stacks and still force gases up through the trap.?.

The part I still don't like is that an AAV requires inspection and replacement, where as a proper vent through the roof is the time tested proven way to do it.