Loop vs AAV (weird installation)

I had this as a specific "how do I lower my drain" question in the remodel forum, but after doing a lot of research today, I think I narrowed down my options to what's below.

Quick story: sink too deep, disposal outlet even with existing drain. Walls up, many cabinets already installed, don't want to lower the drain in wall for structural reasons too.

HJ quickly showed me I could not use my existing drain to tie into the vent system (too low). But after looking at island installations, I was wondering if it would work with a high loop, which I have space for. Picture below. The other option I have is simply capping the drain line and using an AAV and going through the floor of the cabinet. Both installations tie in at the basement (unfinished). I'd rather avoid the AAV, as I'm leery of anything mechanical that can fail (and have me not notice for a while). I wish I had a better option, but we already have the sink, disposal, and specialty mounting flange (and can't return them), and even a smaller disposal only buys us a 1/2" or so more height.

AAVs are allowed here (Virginia).

All advice appreciated!

Anthony

That is not a loop vent. And the problem is , no part of the vent can be less that 45º angle until it is 6" above the top of the sink. If the sink backed up, that vent would clog. It would have a tendency to get waste in it even in normal operation.

Hi Jimbo,
How does that differ from an island loop vent where the whole thing is below the sink? I'm just having trouble picturing that.

Very unlikely an inspector would allow you to use an island vent when you can obviously do a proper installation. The fact that it is not convenient for you will NOT be of concern to him!

Well there was no permit on this since it was supposed to be a remove one sink and replace it with another install (in the same place). I'm just trying to do something that works.

My issue with relocating the drain isn't a matter of convenience, it's a matter of structure. More than half of two load bearing studs was cut away to get the drain line to an intermediate drain/vent and then join the stack. Re-working this would require cutting at least 2 more inches down into the notch. It's only a 2x4 wall, so I doubt this would even be allowed now. I know walls are overbuilt, but as an engineer (mechanical), I am way concerned about this. If it was only one stud, I wouldn't care.

This may all be moot since I inspected my basement and this drain is directly over the electrical panel with a nice HVAC duct in the way. So between the wires and duct, I doubt I'd have the room to return it to the stack.

Off to plan C or D, whatever they might be.

YOur "high loop" will ONLY WORK, and it is still marginal, if it is ALL THE WAY up against the bottom of the countertop. Even then, if the "new" drain gets plugged, once the water filled the sink to a certain level, vefore it could overflow it would start using the "vent" as a drain, which is why the "minimum" distance above the floor is enforced.

Yeah, that was what I was thinking / worried about -- but also thinking since that was a double/drain vent, it would have two paths to drain, which may be better, but I understand why the code is the way it is.

See my later post, though, I don't think I have enough room in the basement to plumb this without moving HVAC, which would quickly make this just as tedious / expensive as reframing.


Different direction: what would you all consider the minimum distance (center to center or bottom to bottom) between disposal discharge and drain? The manual I have (disposal) says 1/4". The P-trap I have can accomodate 1" without modification. I will be 1' away from the wall so I need 1/4" for that as well. I think I could cut the compression fitting that the discharge pipe goes to by 1/2", but that's it.

We are looking at raising the sink to a proud mount (gets us 1-1/2", but has other issues -- design compromise) or a new sink that is a bit shallower (Kohler Whitehaven line -- throwing money at the problem), but even there, we are looking at 3/8" to 1/2" offset. If I downgrade to an ISE Compact, I get another 11/16" back, which puts me around 1-1/4", which I could live with, but that's putting an extra $1k into the project (but I'll have an extra sink and disposal )

Thanks again guys.

What kind of countertop is this? Is it an option to shim up the whole counter by 1/2" or so? That would raise your disposal and allow you to leave the sink undermounted. This usually works with counters that have a front lip, but not always if you don't have that. You might have to run a trim piece between the cabinet and the counter if you go that route with counter that doesn't have a front lip, but it still may be a lot less hassle than what you're describing.

Soapstone, 1-1/4" thick. The cabinets are a standard 34-1/2" off the ground. There's no lip, so a gap that big would show.

I'm getting quotes for custom sinks, which I can get 8" deep and solve the problem -- then I'd have an extra Rohl sink which would end up being the most expensive utility room sink ever.

The other option is mounting the existing sink 1/2" proud of the counter, which the wife is researching to see if she'd like it. No drainboard and she's worried about stained caulk, crumb catching, and pots nicking it (all valid concerns).

quote; but also thinking since that was a double/drain vent, it would have two paths to drain, which may be better,

WRONG! It would be worse, which is why it is not allowed. When one path plugged, you would NOT know it until the second one also plugged. BUT you would probably ONLY unplug the initial path, NOT the "vent". The UPC drawing is incorrect for the same reason. The "foot vent" CANNOT connect to the "vent riser" below the floor. It ALSO has to connect to the vent 42" above the floor, just like any other vent connection. The way it is drawn, the "foot vent" CAN become a "second drain route".