Venting Toilet Fixture Arm

I'm plumbing a new upstairs toilet. The way I have it currently laid out, the toilet flange goes through the floor, immediately connected to a 90 degree sweep. There's 7" of horizontal pipe on the end of the sweep, then a combo that ties in to the main stack. Nothing enters the stack above this combo, it goes up and vents through the roof.

So, the question is, does this meet venting requirements. The fixture arm itself is not vented, and, because I have a combo on the main stack I could see the AHJ saying that air couldn't get back up the fixture arm. I could see changing the combo to a sanitary tee, that would reduce the vent blockage (I think I could show a clear path for air from the top of the tee into the fixture arm, since my drop is only about a 1/4" in the arm). Or, do I need to add a fitting and vent the fixture arm?

I'd love to leave it as is, but now I'm having second thoughts about whether or not the inspector will like it.

Which plumbing code does your town go by¿ The IPC does not require a toilet be vented as it is a self siphoning fixture.

Connecting the new water closet into an existing vent stack will end up wet venting all the fixtures below, which will violate plumbing codes.

Sorry, forgot those key details.

UPC - IRC would be no question

Everything else below is vented separately, won't have a wet vent on lower fixtures. Some of those vents tie in to the stack in the rafters above this toilet, but that should be OK as above the FL of the toilet.

AS long as the fixtures below are all vented above the new bathroom you should be fine.

With the new WC there are only three fixtures on the entire drain system; another toilet one story down and about 15' horizontally from this, with a 2" vent that comes up to the main stack just below the roof, and a kitchen sink that vents separately directly above itself. The main stack only got run out to its location because there was a wall wide enough to hold it at that location. Which just happens to be where I want to put the new fixture.

The whole rest of the house is on a separately plumbed and vented graywater system. Sometimes a pain, but it makes this addition easier, since there really are no fixtures in the system.

Have a look at this drawing. If you tie anything in the orange area you be wet venting the all the fixtures below. Lets say the bathtub and the sink tie in higher than the drawing is showing and they are currently using the vent stack to vent the lav,water closet, and shower, you would be wet venting the bunch.

DSanduril said:

With the new WC there are only three fixtures on the entire drain system; another toilet one story down and about 15' horizontally from this, with a 2" vent that comes up to the main stack just below the roof, and a kitchen sink that vents separately directly above itself. The main stack only got run out to its location because there was a wall wide enough to hold it at that location. Which just happens to be where I want to put the new fixture.

The whole rest of the house is on a separately plumbed and vented graywater system. Sometimes a pain, but it makes this addition easier, since there really are no fixtures in the system.

Click to expand...

If thats the case the vent stack you are tying the new water closet into will serve as your vent then. So all is good.

toilet

The toilet is the only fixture that you can use a combo to make its connection, assuming the inspector realizes it. With a sanitary tee, there is no ambiguity about whether it is proper or not.