Island/Peninsula Loop Vent - Final Check

[Richard Ellis]

First I would like to thank Terry and this forum for the many posts on island loop vents. My familiarity with them, all from what I learned here, impressed my city inspector for a DIY'er.

Before I complete final glue up of my peninsula loop vent, I would like input on heights of the cleanout and the sanitary tee for the p-trap.

A few comments about my design, as you look at the picture:
1. I will be adding a 2nd layer of T&G plywood on the floor in the kitchen to meet TCNA specs for deflection for a tile installation.
2. My finished floor elevation will be at the top of the 2x4 of the sill for the knee wall behind the counter (T&G + mortar + DITRA + mortar + tile). So I based my measurements from there.
3. Cabinets will be installed on top of tile floor
4. My peninsula has no bar, which is why I am using a loop vent
5. My AHJ reviewed my plan and approved the use of a loop vent. They don't allow AAV's, and I know general consensus on forums is that plumbers prefer designs with no moving parts.
6. TruGranite sink. Depth: 7-1/4 to 9-1/2 depending on model
7. ISE Evolution 3/4 Compact Disposer

Questions to Answer...

• Any issues with height of the p-trap connection?
• Any issues with height of the cleanout?

Note the ruler positioned at the top of the sill is at 2", not 0.

Loop Vent Photo

Rendering of my peninsula for context (done in Home Architect by me )

Here's a picture showing the offset I had to do to bypass the existing vent line.

Thanks in advance.

 

[Asktom]

Usually with an island sink vent setup the foot vent takes off under the floor because otherwise there is normally a simpler, easier way to do it. But, I don't see anything wrong with doing it above. Under the UPC and a strict instructor where the vent takes off to the side you should have used a combination rather than a san tee. You need a clean out on the vent at the point where it turns upward or on the vertical. Also, it looks like you are stubbing out 2" for the sink trap, 1 1/2" is normal. I really don't know exactly is happening below the floor, but that horizontal line has a lot of turns without a clean out.

 

[Sponsor]

 

[Stuff]

For my education what does this mean? "My peninsula has no bar, which is why I am using a loop vent"

Is that the vent going horizontally to the right? If so why couldn't that have been the trap arm instead of doing a loop? Or take it up at a 45 angle to use as a normal vent?

 

[CountryBumkin]

You may want to lower the drain pipe - or at least be aware that if you install a "deep sink" with a garbage disposer you may find the disposer's outlet might end up lower than the drain pipe, in which case you have an issue.

 

[Richard Ellis]

Usually with an island sink vent setup the foot vent takes off under the floor because otherwise there is normally a simpler, easier way to do it. But, I don't see anything wrong with doing it above.

My intent was to run the vent under the floor, but during fit up, I wasn't able to get the slopes of the vent and drain to code (1/4" / ft) without running in to the floor trusses. That is when I asked the AHJ and just raised it above the floor.

I am interested in the simplier, easier way if you can to explain.

Under the UPC and a strict instructor where the vent takes off to the side you should have used a combination rather than a san tee.

I asked my inspector about that. He indicated the san tee was acceptable. Just had to make sure the direction was right.

You need a clean out on the vent at the point where it turns upward or on the vertical.

Based on threads and other pictures I found on the Internet, I asked about clean outs also. My city inspector said he would not require it. I have all of the fittings to install one if you as professionals recommend it. The vertical vent on the right runs in a wall behind the refrigerator so it will be accessible but hidden.

Also, it looks like you are stubbing out 2" for the sink trap, 1 1/2" is normal.

I wondered about that. The original kitchen sink had the 2" stub out, so I went with that. If 1-1/2" is typical, I will go with that.

I really don't know exactly is happening below the floor, but that horizontal line has a lot of turns without a clean out.

The vent line to the right that rises up through the roof in direct line with the 2" drain that goes down to serve the unit below. It is not possible to run the drain from the sink directly in line with where it drops down through the floor. Otherwise it runs in to the vent line. The original drain line had the same jog.

 

[Richard Ellis]

For my education what does this mean? "My peninsula has no bar, which is why I am using a loop vent"

By "bar" I was trying to refer to the elevated section that typically gets built behind the sink. The original kitchen sink had one -- the wall where the two receptacles are installed, and then the short countertop gets installed. I wanted my countertop to be flat all the way from the kitchen in to the living room.

Is that the vent going horizontally to the right? If so why couldn't that have been the trap arm instead of doing a loop? Or take it up at a 45 angle to use as a normal vent?

Yes, it is the vent. I didn't tie it to the trap arm, because when I started this -- I was mimicking an island vent, where the vent line is actually run in the floor. As I mentioned in the post above, I was not able to get the drain and vent lines in the truss spacing. So I checked and got approval to move it above the floor. Code states that the vent is supposed to rise vertically at least 6" above the flood level of the sink before it starts a horizontal run.

Since I can't do that directly above the san tee for the p-trap (because the "Bar" section is gone), I did not think it was legal to just run a vent up at a 45 like a regular vent.

In retrospect, I'm wondering if the whole loop vent thing is necessary. Thus the reason for my post.

 

[Stuff]

I think I understand now - no backsplash behind the sink where you were thinking of turning the vent horizontal.

What is the distance from the sink stub-out to the vent stack behind the refrigerator?

Here is another thread with your issue (skip 1st pic): https://terrylove.com/forums/index.php?threads/kitchen-peninsula-venting.35075/

 

[Richard Ellis]

I think I understand now - no backsplash behind the sink where you were thinking of turning the vent horizontal.

This is exactly my case.

What is the distance from the sink stub-out to the vent stack behind the refrigerator?

Distance is approximately 50". Here is a view of the whole installation.
Drain length: 58.5", so I calculated the drop needed = 1-1/4"
Vent length: 49", so rise needed = 1"

From the other thread, I think I understand that if the distance were short enough, the I could have avoided my loop and vent line altogether, and just run a drain line directly from the trap over to the vent. Then cap the original 2" drain line under the floor to the right.

For clarity, I have already glued up the 2" horizontal section under the floor. Only the vertical portion of my install are "dry" at this point.

 

[Stuff]

Quick search shows Texas under IPC. Therefore 1 1/2" trap to vent distance is 6' - you would also need to count in the distance from the wall stub to the actual trap.

I found this IPC definition: VERTICAL PIPE. Any pipe or fitting that makes an angle of 45 degrees (0.79 rad) or more with the horizontal.

So if you then added a bit of 45º it would shorten the distance and would be fairly clean. Not perfect but AHJ should be OK with it.

I'm not a plumber but try to respect what they do - more brains than brawn.

 

[Cool Blue Harley]

Quick search shows Texas under IPC. Therefore 1 1/2" trap to vent distance is 6' - you would also need to count in the distance from the wall stub to the actual trap.

I found this IPC definition: VERTICAL PIPE. Any pipe or fitting that makes an angle of 45 degrees (0.79 rad) or more with the horizontal.

So if you then added a bit of 45º it would shorten the distance and would be fairly clean. Not perfect but AHJ should be OK with it.

I'm not a plumber but try to respect what they do - more brains than brawn.

View attachment 37595

Great post Stuff.

That is the solution. Also keep in mind that rolling the garbage disposer outlet ell to the right gives you five inches, and the offset of an adjustable p-trap is three inches, potentially reducing your trap arm length by eight inches. Never want to stub out directly behind the disposal.

I have serious questions regarding the AHJ.

 

[Richard Ellis]

Back to share the finished product. Unfortunately, some of the installation is hidden under insulation which I installed behind where the dishwasher will go to help deaden noise. I lost some photos when I switched phones and learned my SD card was encrypted.

Here is after the drywall has been installed...