Bathroom wet vent sizing

[drhing]

Hi,

I'm trying to follow IPC code, but I'm not sure I have this right.

The 4" combo wye is below a WC and to be plugged upstream with a C/O. The 2" pipe is the tub trap arm connected to a 2" combo wye draining a Lav and venting through the roof. The 2" drain for the lav is the Wet Vent for the WC and the Tub.

Questions:

a. Based on table 912.3 looks like my vent needs to be 3". Am I reading the code correctly, or will my layout work?

b. Can I connect the tub into the upstream side of the combo and call it a horizontal wet vent, or does it have to connect via a wye downstream of where the wet vent goes horizontal?

c. Any other issues here, or suggestions?


Thanks!

 

[wwhitney]

a) No, you are misapplying table 912.3. The DFUs listed are for the fixtures draining through the wet vent, and do not include the fixture being wet vented. So the pipe carrying the tub and the lav has only 3 DFUs draining through it and may be a wet vent at 2". Also, that 2" combo at the bottom middle of the page, where the tub trap arm comes in horizontally and the lav drain/wet vent comes in vertically, it could be a 1-1/2" vertical drain/wet vent coming from the lav, since that pipe is only carrying 1 DFU.

b) Yes, the arrangement with the upright combo, the tub trap arm coming in horizontally, and the dry-vented lav coming into the top (side) entry is fine and complies with the horizontal wet venting rules.

Cheers, Wayne

 

[Sponsor]

 

[drhing]

Ahh, that makes sense! Thanks Wayne.

I didn't see mention of the WC, which is also utilizing the Wet Vent. Could the lav drain be 1.5 inclusive of the water closet, or would the Water Closet require it's own vent?

a) No, you are misapplying table 912.3. The DFUs listed are for the fixtures draining through the wet vent, and do not include the fixture being wet vented. So the pipe carrying the tub and the lav has only 3 DFUs draining through it and may be a wet vent at 2". Also, that 2" combo at the bottom middle of the page, where the tub trap arm comes in horizontally and the lav drain/wet vent comes in vertically, it could be a 1-1/2" vertical drain/wet vent coming from the lav, since that pipe is only carrying 1 DFU.

b) Yes, the arrangement with the upright combo, the tub trap arm coming in horizontally, and the dry-vented lav coming into the top (side) entry is fine and complies with the horizontal wet venting rules.

Cheers, Wayne

 

[wwhitney]

In your arrangement, the wet vent consists of two parts:

a) The lav drain from the dry vent connection to the tub connection. This portion carries 1 DFU and may be 1.5" under the IPC (but 2" is good and would be required by the UPC, FWIW). It wet vents the tub.
b) The combined lav/tub drain from the lav/tub wye to the wye with the WC. This portion carries 3 DFU and must be at least 2". It wet vents the WC.

I'm assuming you're not wet venting anything else downstream of the WC (like another bathroom). I'm not sure I followed your question, but hopefully the above clarifies.

Cheers, Wayne

 

[drhing]

Well, my question was not really clear, or significant for my application because I am running 2" minimum everywhere and your explanation makes it clear that what I was hoping to do will work .

But, just for kicks, my attempted question rephrased; could the wet vent from the lav to the combo wye be 1.5" as you mentioned, even though it is wet venting a 4" toilet (as 4" drain requires minimum 2" vent per table 906.1 assuming I am interpreting this table correctly)?

Thanks again

In your arrangement, the wet vent consists of two parts:

a) The lav drain from the dry vent connection to the tub connection. This portion carries 1 DFU and may be 1.5" under the IPC (but 2" is good and would be required by the UPC, FWIW). It wet vents the tub.
b) The combined lav/tub drain from the lav/tub wye to the wye with the WC. This portion carries 3 DFU and must be at least 2". It wet vents the WC.

I'm assuming you're not wet venting anything else downstream of the WC (like another bathroom). I'm not sure I followed your question, but hopefully the above clarifies.

Cheers, Wayne

 

[wwhitney]

But, just for kicks, my attempted question rephrased; could the wet vent from the lav to the combo wye be 1.5" as you mentioned, even though it is wet venting a 4" toilet (as 4" drain requires minimum 2" vent per table 906.1 assuming I am interpreting this table correctly)?

Table 906.1 only applies to stack vents and vent stacks (see the definitions), not to branch vents, individual vents, etc. So for stack vents and vent stacks, the minimum vent size is half of the drain size installed. While for other vents, the minimum vents size is half the minimum drain size that could be used (906.2).

In other words, since your 4" drain could be a 3" drain, a 1-1/2" vent suffices.

Cheers, Wayne