Island Sink Drain Plumbing

[Bob S]

I am having a home built and the kitchen has an island that will incorporate a sink and a dishwasher. When I look at the plumbing that they have put in for this something does not look right. The attached picture shows the configuration. They have the loop going up to the sink flood level but the loop does not go anywhere. It looks like it just traps air. There is a vent system for the house drain and all of the other drains have a vent that goes up to that vent system but the only way that the island drain is tied to the vent is by the drain. My concern is, will this work? I have Googled this type of drain and found diagrams etc. that show something similar but it looks to me like this plumbing job is missing a key component. somewhere to vent the air. I am fairly familiar with plumbing but I have never dealt with and island drain before. I am hoping that some of you who are versed in this type of drain can help me out here. Thanks in advance.

 

[justin_dewan90]

It's a loop vent, should work. See them all the time for island sinks.

 

[Bob S]

This is one that I found on the internet. It loops to a vent. The one in my house just loops back to the drain. Will these two very different configurations both work equally well?

 

[TomFOhio]

We always did them similar to the second picture. Come up with your drain and put a tee in and
stub out and take vent up as high as possible and go back down through floor and tie back into
the drain with a tee wye and then put a dishwasher wye in the sink drain or disposal. After a many
years they didn't make us do the island vent, as they started letting us use an AAV. The drain system
had to be 2". Could be different where your at.

 

[voletl]

That is done incorrectly. The loop must tie into a vent below the floor. Whoever did this justed wyed it into the drainline creating a pointless loop that will do nothing

This pic is one way to do a proper island vent

 

[justin_dewan90]

If you could show a picture of underneath it, in your basement or whatever. That would give us a lot more information.

 

[Bob S]

Thank you Voletl. That was my concern. As far as I can tell the loop does nothing. I cannot find any examples where the loop just goes back into the drain. If anyone knows of any I would be interested in seeing them. I know my builder will tell me his plumber does them like this all the time and they work just fine. I think his plumber dies not know what he is doing. Justin, unfortunately this is a cement slab. As far as I can see this drain was not included in the plumbing vent system. I know they make some kind of vent valve they you can use instead of a pipe vent but I really don't want a mechanical vent.

 

[Zanne]

How far is your island's plumbing from the nearest wall with a vent pipe? Sometimes the loop isn't necessary if a vent is accessible within the accepted distances. For 1.5" pipe, I believe it would need to be within 5 feet.

 

[justin_dewan90]

It's 5 feet where I'm at.

 

[voletl]

Using a common vent would not work the piping setup would create an S trap. If you're on a slab you might as well bite the bullet and put it in mechanical vent that is accessible in case you need to change.

 

[TomFOhio]

Your correct . I got my code book out and we did put in the vent down below. Should of got my book out first.
Have you ever put in the AAV?

 

[justin_dewan90]

AAV vents are fine, just need to be accessible. Other thing is they need to be above the sink in case of a back up. But thats different from city to city.

 

[Bob S]

I need to go and look tomorrow with fresh eyes thanks to all of your comments. I'll post back when I get more details. I need to do some research on mechanical vents. Thanks again for all of your help.

 

[TomFOhio]

That is done incorrectly. The loop must tie into a vent below the floor. Whoever did this justed wyed it into the drainline creating a pointless loop that will do nothing

This pic is one way to do a proper island ventView attachment 17360

I'm not sure what venting system I was thinking of. I thought that we brought the vent line back into the
2" drain underneath and it used the top of the drain inside for the vent. Its been quite a while since I have
done an island vent. Has anybody ever heard of this.

 

[Diehard]

The diagram shown by voletl is the typical method shown in the Mass Plumbing code. And I suspect all plumbing codes would be the same for an Island vent. It is referred to as a BOW VENT.

Many plumbing codes are accessible on the internet but they don't all include diagrams, which are a big help. Mass Plumbing code includes diagrams.

 

[Bob S]

The closest wall, period, is about 12 feet. Can vent line vertical pipes not be that far from the fixtures they are venting?

 

[voletl]

In your case it does not matter whether the vent is 12 feet or if it's one foot away. If the Trap does not have contact with air from the vent it will create a siphon pulling water out of the Trap. A S trap will be created

 

[wood4d]

island sinks in the middle of a room ive done lots need to use a studor vent. The "loop" vent is something I did for 20 yrs because the inspectors approved it. The vent voleti posted is right on out of the codebook but takes hours to do. The studor vent is a 5 minute fix and is mostly universally used. It is not an AAV

 

[voletl]

If it took me hours to do an island vent I think I would be fired but cheater vents do make it easier

 

[wood4d]

in the dirt it takes hours