Island Sink Venting

[Gese]

Hi, I have read so much on this topic that it has literally spun me in knots. I am not a pro and would like to do some of the plumbing work myself. Not new to plumbing and quite handy but I also want to do things right so I read more than I should have on island Sink Venting.

Here is my situation. I am moving a kitchen sink from a wall to an island in the middle of the kitchen. There is a 1.5" vent abs pipe that goes straight through the roof and straight down to the basement. I live in a bungalow. The sink was the only fixture (along with the normal dishwashwr setup) that was connected to this vent. The pipe above the ptrap worked as a vent while the pipe below worked as a drain. In the basement, the 1.5" pipe connects to a cleanout and then to a 4" abs pipe that runs under the basement concrete slab. I never had any issues with this set up and I believe this "wet" is as oer Ontario Cda code.........I bought off a builder so I am the original owner. The floor joists are TJIs and unfortunately the plumbing belibthe kitchen floor is limited .(about 7" or so........and I will have to bore through the membrane of the joints because they do not run in the right direction towards the 1.5" pipe I mentioned above. How will I run the drain and vent for the island sink? Can I connect the sink ptrap to a vertical 1.5 pipe that goes straight down to below the kichen floor (within the sink cabinet) and then put 1.5" long sweep 90 with a regular 1.5" downward sloping 1.5" abs pipe that connects with a tee to the roof 1.5" vent I mentioned earlier. The section above the tee will be the vent while the section below the tee will act as the drain? I will put a cleanout under the sink as well. Would really appreciate the help of the good folks in this forum

 

[Terry]

You will need to add an AAV at the kitchen sink too. The vent at the wall isn't helping you, but you do need to either keep that one draining from the roof penetration, or pull it out completely. Normally a kitchen sink is 2" for the waste line, and 1.5" for the p-trap, trap arm and vent.

 

[Sponsor]

 

[Gese]

You will need to add an AAV at the kitchen sink too. The vent at the wall isn't helping you, but you do need to either keep that one draining from the roof penetration, or pull it out completely. Normally a kitchen sink is 2" for the waste line, and 1.5" for the p-trap, trap arm and vent.

Hi Terry, thank you for your response. I just want to understand this. The vent pipe that is currently in the vertical wall served as a vent and drain for the sink that was mounted along the kitchen wall. This pipe vents straight through the roof and drains straight down to my basement, through the concrete slab and presumably ties into the drainage system of the entire house. There are no other connections to this vertical section. I believe this is sometimes referred to as a "wet vent".

It appears to me that this existing "wet vent" is my most convenient option to tie the sink that I am moving to an island. The sink will be 7 or 8 feet away from this existing vent. Couldn't I "simply" run a pipe from the island down and under the kitchen floor sloping towards the existing wet vent? I would connect using a tee. Have I described this properly?

 

[Terry]

I understood what you meant.

This is an Island Vent

There is a waste line going down and a loop vent going up. Venting takes place above the trap arm, not below. This Island Vent keeps the vent dry at all times. It's not a wet vent.

In this layout, the venting is above the trap arm. The portion that is wet is for the lower fixture, which is also going up for the vent.

Wet venting is allowed for bathroom fixtures but not for kitchen sinks.

Examples of wet venting for bathroom groups. Not kitchen sinks.

A typical kitchen sink layout.

 

[Gese]

I understood what you meant.

This is an Island Vent

There is a waste line going down and a loop vent going up. Venting takes place above the trap arm, not below. This Island Vent keeps the vent dry at all times. It's not a wet vent.

In this layout, the venting is above the trap arm. The portion that is wet is for the lower fixture, which is also going up for the vent.

Wet venting is allowed for bathroom fixtures but not for kitchen sinks.

Examples of wet venting for bathroom groups. Not kitchen sinks.

A typical kitchen sink layout.

Hi Terry, I realized after sending my note that the Venting is required above the trap. Thanks for that. My current kitchen sink is as per the image you provided below except my dishwasher was not connected to an air gap fitting.

So this was my starting point. Moving the sink to an island, I still want to make use of that vent pipe that goes up through the roof as well as the drain part of that same pipe (let's call it the "Stack"). I assume I will then use the typical island vent (with loop) that you also provided. However, the lower drain pipe below the floor will connect to the Stack beneath the floor and with the joint cavity. The lower vent pipe below the floor that is also coming from the island, will also connect to the Stack but I believe I will need to run it up parallel to the Stack and connect to the Stack approximately 6 inches above my island countertop. Is that correct? Assuming I do not use an AAV that is. Note that the Stack appears dedicated to this kitchen sink......other than possibly providing possible venting to the drainage system under the basement slab. Again thank you for any help you can provide.

 

[Gese]

Hi Terry, I guess what I am trying to say is that if I don't use an AAV but use a loop vent as per your diagram, can both the vent pipe below the floor and the drain pipe below the floor, connect to my Stack? If so, where on the Stack?

 

[Terry]

Looking at the 1.5" vent on the right of the picture, that would be your existing vent through the roof.
The Loop return would run toward the outside wall and connect downward on your old kitchen drain below the floor.