Loop vent question: waste connection

[Riosman]

I'm installing a loop vent for an island sink. This is for a room addition. I would like to make the loop vent waste connection up stream of the sink waste connection. The two books I have show the vent return to the waste line down stream from where the sink connects to the waste line.

Does it matter where the loop vent connects back to the waist line?
Could it even be a different waist line than the sink it is servicing?

Riosman

[shacko]

A island vent has to hook-up to the waste line after the trap, not upstream. it has to tie into the waste line that the trap is connected to. You usually have to increase the drain one pipe size. Luck.

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"If you don't have the time to do it right, where will you find the time to do it over?"

[Riosman]

The reason for connecting the loop vent return to the waste line upstream from the sink connection to the waste line was to avoid boring through a floor joist. I can still do this by adding two 90's or 45's to get to the other side of the sink connection.
The vent line is 1 1/2 dia and the waste line is 2 inches .

Thanks for the reply

Riosman

[Phil H2]

I don't know about the IPC/IRC. But, the UPC does not allow it. It says that connection for an island vent must be made immediately downstream. Also, When connected to a horizontal drain, any vent pipe must take-off above the centerline of a drain pipe.

[hj]

As a practical matter it doesn't matter which pipe is the drain and which is the vent, as long as the one you decide to use for the vent has a lateral vent which eventually goes out the roof. The lateral pipe is the "vent' and the connection back to the drain is a drain to eliminate any condensation or backup that gets into the loop vent piping.

[Winslow]

This is an illustration of an island sink according to the UPC. The illustration however shows the cleanout on the wrong portion of pipe. It belongs on the vertical section that extends through the roof, which allows you to clean the foot vent.

[ToolsRMe]

This is an illustration of an island sink according to the UPC

I am not a plumber ... but that just doesn't look right.

Am I seeing it right that the main drain line ties into the vent stack???? That would block gases from the sink from escaping.

[hj]

You are seeing right, and it is correct, although this is just an example. I have installed them with the vent on either side depending on which is easier as far as the lateral vent connection is concerned. Without that drain connection condensation could fill the "trapped" portion of the vent and plug it. It works because the drain does not need air until the sink is almost empty and by that time the horizontal line is no longer full of water that could have risen in the vent pipe and blocked off the lateral vent.

[Cass]

An AAV, if allowed where Riosman lives, would simplify thing greatly.

[Mikey]

So the vent lateral must be sloped as a drain, I assume? (Downward from the stack.) It would slope to the drain line, so it depends on what you call the stack.

[Winslow]

So the vent lateral must be sloped as a drain, I assume? (Downward from the stack.)

Actually that portion of pipe is called the foot vent (UPC terminology), and yes it slopes toward the drain. The loop equalizes the pressure on both sides of the trap to stabilize it.

[Riosman]

Well I reversed the connection so the vent connects downstream from the waste connection as shown in the picture. It doesn?t seem logical but I noticed all views shown of a loop vent show it this way. I do have a twist. The lateral vent takes off 90 degrees from how the picture is shown to run between the floor joists and to the nearest vertical wall then up and out the roof. The horz.vent line maintains a ¼ per foot slope to the drain.
I wanted to avoid boring several holes thru consecutive floor joists to get out is the reason for the 90 degree approach. Boring the holes would not pass inspection due to violation of the min edge distance of the hole and the joist edge.

[Winslow]

Well I reversed the connection so the vent connects downstream from the waste connection as shown in the picture. It doesn?t seem logical but I noticed all views shown of a loop vent show it this way. I do have a twist. The lateral vent takes off 90 degrees from how the picture is shown to run between the floor joists and to the nearest vertical wall then up and out the roof. The horz.vent line maintains a ¼ per foot slope to the drain.
I wanted to avoid boring several holes thru consecutive floor joists to get out is the reason for the 90 degree approach. Boring the holes would not pass inspection due to violation of the min edge distance of the hole and the joist edge.

The foot vent has to come off the return vent(the vertical pipe coming down from the top of the loop). You cannot take it off the drain line. (as it sounds by your description.)

[Winslow]

I am not a plumber ... but that just doesn't look right.

Am I seeing it right that the main drain line ties into the vent stack???? That would block gases from the sink from escaping.

It doesn't look right because you are not a plumber. The sewer gas escapes through the foot vent. The return vent equalizes pressure on both sides of the trap (preventing unequal pressures on either sides of the trap seal. )

[Riosman]

The foot vent connects to the loop return above the drain just as shown in the picture. I changed the course of the foot vent so it doesnt run in the same direction as the waste drain in order to avoid floor joists. I also took the shortest route to the nearest wall.