Island Vent Install-with little clearance in floor below

[Northbeard]

Hello,
long time reader, first time poster! I really like this site and appreciate Terry and all the other guiding lights here. Thank you. I wasn't sure if I should join an existing thread or start one, I couldn't find a recent one that made sense so new thread. Apologies if this is not cool.
I am putting in an island vent to get rid of the ridiculous wall in the middle of my kitchen (osb on the right). There is not much clearance in the basement because of the joist direction and the drop-down ceiling. I had intentions of following the drawing I made but best laid plans...If I stack two combo wyes I get way too low and into the drop-down ceiling. The drain is about 5' away and the vent needs to go 6' then up.
I am curious what I can do at the ? to make this happen. I read a years old thread about rolling 45s...it seemed feasible but I can't seem to shake out the geometry of it for my application. I want to add a 45 wye at the ? but I don't like the directional flow it creates even if it is twisted a bit.
Thank you for taking the time.

 

[Reach4]

https://terrylove.com/forums/index.php?threads/island-sink-venting.43049/ has discussions on the merits of using an AAV for an island.

 

[Sponsor]

 

[Terry]

The wet portion of the Island Vent is 2" and the vent portion can be 1.5".
The clean out is under the sink and accessible.
For the downstream foot vent, you can use a 2x1.5" wye tilted up some and pull the foot vent off of that and coming off the wye head toward your far location. That will need a cleanout that is accessible too.

The combo below would be replace with a wye further downstream so that you can lay the combo on it's angle with a long 90 going up for the loop.
Maybe that's understandable. I have done them not so vertical below.

 

[Northbeard]

Yup, I have the cleanout in the island vent under the sink, tough to see but it is in the first picture, just below the p-trap adapter.
I am a little confused, I can put a wye where the last combo is and then the combo? or do I add a wye after the combo and twist it so the drain goes one way (down) and the vent the other?
Once the vent gets started it is pretty somewhat clear, same with the drain. I just need this transition situated.
I am trying to avoid an AAV

.
Thanks.

 

[Terry]

I'm sorry, the extra vent comes off the loop before it enters the waste portion of the line at the bottom. I'm having a hard time even putting it in my head right now. A 2x8 joist space doesn't give you much room. Most of my work has been with 2x10 or larger.

 

[wwhitney]

As I understand it, the foot vent needs to come off the vent loop at a higher elevation than the drain. To minimize the height gap between the horizontal foot vent and the horizontal drain, for my island bar sink (1-1/2" drain) I rolled the stacked wyes 45 degrees off vertical. And I used a street wye for the upper wye.

There's a photo below, looking up from the basement. The cast iron is the 2" main sink drain, which can be ignored for this discussion. The fitting with a cleanout is the underside of a combo, with the hidden upper inlet being the bar sink drain. The other leg of the vent loop comes through the floor at an angle at that blob of fireblocking foam that appears just to the right of the cast iron drain. Then the street wye provides the foot vent takeoff, and the bottom wye with the grey strap connects the drain to the vent loop.

Not 100% sure this is all up to snuff, but the inspector liked it fine. The cleanout is superfluous, so that combo could be a long turn 90 instead. And this arrangement is for where the horizontal drain and foot vent run in opposite directions away from the loop vent. But I bet something similar could be done for other desired directions of running the foot vent.

Cheers, Wayne

 

[Northbeard]

My drain and vent run in the same direction, then split 45 or so. My joists are perpendicular to the island vent so I need to get below them with as little contraption as possible. That's why I am abandoning my original drawing.



The upward (or downward) wye could do that but it doesn't seem right, that seems like a waste/vent combination.



I need to invent that fitting, a combo H for that vent/drain reunion.



I have 6" or so under the joist to work with, I thought if I could stick the top of those combos in the joist bay I could split but that seems unlikely.



What if there was a downward (45) wye, or a combo between them that headed to the drain? Triple combo?

 

[Northbeard]

As I understand it, the foot vent needs to come off the vent loop at a higher elevation than the drain. To minimize the height gap between the horizontal foot vent and the horizontal drain, for my island bar sink (1-1/2" drain) I rolled the stacked wyes 45 degrees off vertical. And I used a street wye for the upper wye.

There's a photo below, looking up from the basement. The cast iron is the 2" main sink drain, which can be ignored for this discussion. The fitting with a cleanout is the underside of a combo, with the hidden upper inlet being the bar sink drain. The other leg of the vent loop comes through the floor at an angle at that blob of fireblocking foam that appears just to the right of the cast iron drain. Then the street wye provides the foot vent takeoff, and the bottom wye with the grey strap connects the drain to the vent loop.

Not 100% sure this is all up to snuff, but the inspector liked it fine. The cleanout is superfluous, so that combo could be a long turn 90 instead. And this arrangement is for where the horizontal drain and foot vent run in opposite directions away from the loop vent. But I bet something similar could be done for other desired directions of running the foot vent.

Cheers, Wayne


View attachment 62389

Hey Wayne,

thanks for sharing. I think the advantage you have over me...if we wanna call it that...is that opposite direction. That seems to be an issue for me, that and the 8" joists that are perpendicular. I am starting to consider the AAV...sure would like a cocktail right now at that island bar!

 

[Northbeard]

Okay, if there is anyone with me...here is another idea.
The middle portion of this drawing is an overhead view sort of. My plan is to tie in the island drain to the downstairs kitchen drain (under the p trap). I planned on running the island vent (dotted line) separate and meeting up with the downstairs vent up the vent wall (above the upstairs flood rim). Does that drain tie-in help my situation or is that a wet vent or at least just still a waste/vent combination? There's no way air is going to get back up there right?

 

[Terry]

I think you will have less trouble down the road if you install the AAV there. A lot less fittings, less weird changes of direction and less chance if you snake it later on of winding up going the wrong way and getting stuck.

I think all the new homes in my area with Islands are going with a good quality AAV's.

 

[Northbeard]

NOOO!!!
Yeah, you're probably right. Man, it feels like quitting though.
Any input on a good one?

 

[Terry]

Oatey or Studor make good ones.

 

[wwhitney]

The AAV is surely the simplest solution. But if you are still interested in an island loop vent, a couple options:

Since the foot vent is only 1-1/2", and you only need to cross a few joists, you could just run the foot vent through the middle of the joists. With a 7-1/2" solid sawn joist, you can drill a hole up to 2-1/2" in diameter anywhere in the central 3-1/2" height of the joist. Since a nominal 1-1/2" pipe OD is under 2", that means your holes could rise up to 1-1/2", meaning you could run up to 6' through the joists, i.e. at 16" o.c. through up to 5 joists.

Or you could try a pattern similar to mine, with the drain and foot vent starting off in the same direction. You just have to flip the upper wye around 180 degrees (within the plane of the fitting), which means you can't use a street wye for it. So the pattern will be slightly less compact. It's possible cast iron would be a more compact pattern, as the wyes are all spigot ends for use with no-hub couplings, so you could go connect wye-to-wye directly.

Cheers, Wayne

 

[Northbeard]

With the two combos on top of each other I would be too tall even if I go through the joists. They are not the best joists to begin with, they have been "customized" over the years. I am actually going to be blocking throughout so the AAV route helps that too, less to work around.
Thanks guys, I appreciate the insight and talking it out, I really do.
Take care.

 

[Jadziedzic]

What about a combination waste & vent system for the island sink? If allowed by your local AHJ that eliminates the AAV and the loop complexity. (I read about this in a recent Fine Homebuilding magazine and it seemed intriguing. https://www.finehomebuilding.com/2019/09/10/a-new-old-way-to-vent-a-kitchen-island)

 

[Terry]

What about a combination waste & vent system for the island sink? If allowed by your local AHJ that eliminates the AAV and the loop complexity.

OMG
I saw that page earlier today. Almost none of those pictures would pass an inspection.
They show cleanouts on the wrong side, the wrong fittings on the horizontal, S traps and more S traps.
It hurts my eyes just looking at the pictures there.

 

[Lukewalker64]

The wet portion of the Island Vent is 2" and the vent portion can be 1.5".
The clean out is under the sink and accessible.
For the downstream foot vent, you can use a 2x1.5" wye tilted up some and pull the foot vent off of that and coming off the wye head toward your far location. That will need a cleanout that is accessible too.

The combo below would be replace with a wye further downstream so that you can lay the combo on it's angle with a long 90 going up for the loop.
Maybe that's understandable. I have done them not so vertical below.

Is the below mockup effectively what Terry was describing in this post? I am installing a loop vent in 2x10 joists, so there's not clearance to have the foot vent come off a vertical fitting and still have enough rise to run over to the wall. I've got a wye rolled at 45, so the foot vent comes off above the level of the drain before joining with the sink drain into the main drain line. I think this is effectively the same as what Wayne described/showed in #6, but would appreciate any thoughts if I'm missing something.

Note that for cleanouts, I'm planning on putting one in the sink cabinet on both the drain side and the vent side, as well as in the vent riser in the wall.

 

[wwhitney]

what Wayne described/showed in #6, but would appreciate any thoughts if I'm missing something.

What I described/showed in #6 is schematically below. Basically all I kept from your photo is the wye that is rolled 45 degrees. The straight inlet gets the drain via a LT90. The branch inlet of that wye gets another wye for the foot drain to come off, which then gets a 60 (IIRC) on its straight inlet so that the vent can connect from the vertical.

Cheers, Wayne

 

[Lukewalker64]

Thanks for the quick response, Wayne.

So is the idea that the foot vent has to come off the vent drain line from the island loop above the level of the main drain line? And that the foot vent horizontal run should be above the level where the foot intersects with the vent drain line? Or is it that the foot vent has to come off a vertical (i.e., 45+)?

I've reconfigured similarly, though to save some vertical space, I added a 45 street elbow between the two wyes, so the second wye is horizontal instead of at an angle. Does that work?

If so, is it required to also roll the second wye 45? It would save even more vertical space to have the foot vent split off at the same level the vent drain line turns horizontal.

One added complication here is a joist runs between where the two vertical posts of the loop will go, so I added the extra LS90s to give some extra space between the drain drain and the vent drain.

(attached two pictures to help visualize with all the angles).

 

[wwhitney]

A few comments:

1) Virginia uses the IPC, so an AAV is an option and surely simpler than an island loop vent.

2) The island vent rules in the IPC can be found here: https://up.codes/viewer/virginia/va-plumbing-code-2018/chapter/9/vents#916 You can also read them at iccsafe.org, IPC section 916.

3) What's weird about both your configurations (although not necessarily a violation) is that usually the only horizontal part of the loop vent is the foot vent itself.

Having said that, your first configuration violates the IPC, while the second probably does not. In particular the part of IPC 916.3 that says "The lowest point of the island fixture vent shall connect full size to the drainage system. The connection shall be to a vertical drain pipe or to the top half of a horizontal drain pipe." In your first configuration you have the vent join the drain at a horizontal wye, which would violate the above. While in the second configuration you have rolled that wye up 45 degrees, so the vent connects in the top half of the horizontal drain pipe.

Now I'm not 100% clear on what obstructions you are working around, but in your last mockup, can you turn the LT90 where the drain goes from vertical to horizontal by 90 degrees so that it's outlet points towards the bottom of the photo? That would eliminate a horizontal LT90 in the kitchen drain path, you'd just need one to turn the drain to exit the photo to the left. And then just after that horizontal LT90, can you do a stack up of wyes as per my diagram? Or otherwise eliminate any horizontal vent sections other than the foot vent?

Cheers, Wayne