Reduce 3" vent stack to 2" thru roof

[akadmyster]

Home owner/builder new construction vent question.

California.

I have a two story attached addition I am building.

Does the 3" main stack have to continue through the roof or can I reduce it to 2".

Main stack services a washing machine on the ground floor and one toilet, one double sink lav, one shower on the 2nd floor.

I also have a ground floor toilet with its own 2" vent. Do I have to keep the 2" vent size all the way to the roof?

Thanks guys.

Dana

 

[Ontario Plumber]

Not sure about California, but I know in most places that you have to have at least one stack that continues in 3" all the way through the roof. You have to remember that not only is this venting the fixtures in the home, but also the main 4" sewer that serves the home from the street.

 

[Sponsor]

 

[akadmyster]

All I know is I pulled up California's Venting Code and nothing is said about it.
I must be looking in the wrong place.

I can do 3" all the way up if I had to.... that's what I'd like to find out.
Dana

 

[Asktom]

In California you are under the UPC (or a local variation of it) which does not allow the vent size to be reduced. If by "stack" you are talking about the drain and want to reduce to 2" where the toilet tees off, that is allowed. A toilet requires a 2" minimum vent. With multiple vents the total of the cross-sectional area can't total less than that of the sewer exiting the building. The cross-sectional area of a 2" line is 3.1416" and that of 3" is 7.0686". So, if you only have two 2" vents going through the roof that is not enough. You would need at least another 1 1/2 vent, the kitchen sink perhaps?

A drawing would help, I can interpret your description more than one way.

 

[akadmyster]

OK ... lets see if this diagram is readable and makes sense.

I have the 3" vent stack drawn all the way through the roof.
I can reduce to two inches no problem above the 3" toilet drain junction or anywhere above that. That was my question. Just as easy to leave it a 3" all the way up.

Also ... a dedicated 2" toilet vent from a ground level toilet (on slab) .......... does that have to be 2" all the way to where it connect to the 3" vent stack above the ceiling or can I reduce that to 1 1/2" at some point?

Thanks for the help everyone.

Dana

 

[Terry]

If you have a 2" vent, it continues 2" or becomes larger than 2"

A vent from a lower floor can tie back in at 42" above the "higher" floor. You can't revent below a flood level.

For a three bath home in California, you will need two 2" vents and one 1.5" vent, or one 3" vent.

 

[akadmyster]

See revised vent diagram below.

1. I can do the 3" vent all the way to the roof.
2. I will keep the 2" (ground floor) toilet vent all the way to the 3" main stack above the ceiling,

3. I take it your saying I have to run the ground level washer vent at least 42" above the 2nd floor level before I tie it instead of how I have it drawn .... is that correct?

4. All the other vents tie in above 42".

5. I have the 2nd floor toilet wet vent which also serves as the lav drain at 2" but then I reduced it to 1 1/2" above the drain ..... Is that correct? Based on the ground floor toilet vent having to be 2" all the way up ..... it seems the whole vent system from that point on should be 2"?

6" Do I have to slope the horizontal vent going to the 3" vent stack back to the drain that it serves? Or can it be level with no sags?

Thanks again and very much appreciate your advice.

Dana

 

[Asktom]

The vents you point out must all be 2". The vents must slope 1/4" per foot back toward the drain it serves. The shower drain should connect downstream from the toilet vent. Also, you have two 2" vents connected to the 3" which does not meet the minimum cross-sectional area. Either a 1 1/2" or 2" vent needs to connect to the 3" separately. As Terry said, "...you will need two 2" vents and one 1.5" vent, or one 3" vent". Even though you are going through the roof with 3", you still need to meet the minimum area all the way up or, in effect, you are reducing the vent size.

 

[akadmyster]

I re-did the drawing (now calling it Area 1).
It is color coded to help identify specific areas.

I moved the tub/shower drain downstream from the toilet vent.
I don't understand .... "Either a 1 1/2" or 2" vent needs to connect to the 3" separately."
I think you are talking about the 2" connections I labeled [1] and [2]??

I also have an Area 2 plumbing system with its own 3" stack. One stack on each side of a shear wall. I'm not suppose to have any protrusions going through the shear wall.

In total I will have (2) 3" stacks.
The Area 2 stack will serve (1) bar sink, (1) toilet), (1) Lav, (1) shower.

Can I tie something from Area 1 into this?
I also attached an overall layout.

 

[Asktom]

Moving the tub drain past the toilet vent looks good.

If you have two 3" vents going through the roof then you are not going to have to worry about connecting with two 2" and one 1 1/2" because you will have already met the minimum cross-sectional area. In fact you could either:

(A) in area 1 at the point where the blue 3" line meets the black 3" stack, the stack could reduce to 2" above that tee.

or,

(B) in area 2 where the blue 3" line meets the black 3" tub drain you could reduce to 2" above that tee and go to 1 1/2" for the tub vent.

but, you can't do both unless you also run a fixture(s) on a separate 1 1/2" vent through the roof.

You can connect first floor vents to second floor vents as long as you do so a minimum of 42" above the second story floor. The shorter the horizonal the better.

Another wrinkle is that for each foot of horizonal vent (sloped, of course) you need two feet of vertical unless you bump up the vent one pipe size. I don't know what your distances are but wonder if, for example, the bar sink in area 2 might require a 2" vent for that reason.

In area 2 you show the black stack offset with a minimum of 45s. If you are at least 42" above the floor those can be 90s.

On another note, to be sure I understand your drawing, is there a third toilet (existing?) not shown in your drawing? Is that what the 2" vent that ties in in area 1 is all about?

 

[akadmyster]

3 hours of drawings sure did help.
Thanks for the advice.

There is a 3rd toilet on the ground floor not shown in drawing. The vent line is shown.
I would much rather do your option B and reduce the vent above the Tee to 2" (Area 2) since this is a cantilever area and is real tight.

The distance from the bar sink to the 3" vent stack (Area 2) is about 13' 6". I'll probably do the entire vent system in Area 2 2" just for ease.

So.... because I have two 3" main stacks - both tie into the sewer lateral directly .... I can tie in (Area 1) the two 2" vent lines at areas labeled [1] and [2] .... and in Area 2 I can tie in the (two) 2" vent lines (one from the shower and the other from the toilet) and exit the roof ..... and be within code to make the inspector happy..... correct?

Oh.... do I need a clean out (Area 2) at the end of the 3" run past the bar sink?

And again you have been a great help.
Dana

 

[Asktom]

If the building sewer, the line from the house to the street or septic system, is 3" then option B is good and you can tie in the vents as you say. If it is 4", then the total area of all the vents through the roof must be calculated (I assume there is a kitchen sink there somewhere) to see where you are at. This being an addition, if it was legal before you should be good. I don't have a full picture of what you have.

You don't need a cleanout on the second floor and if you put one it would need to be 3" to be useful.

 

[akadmyster]

You were a big help ... thanks so much for taking the time.
Appreciate Terry's help also.

The kitchen and one full bath is in the existing building with its own vents and should be good.
I installed the new sewer lateral several years ago which is 3" but I believe I hooked it up to an existing 4" which then goes to the main sewer line.

That was all inspected. The city reviewed the plans, knows of all the fixtures, and the plans got passed with the 3".

I am going to proceed as we discussed.

Thanks so much.

Dana

 

[hj]

quote; you are under the UPC (or a local variation of it) which does not allow the vent size to be reduced.

The UPS states that the "the TOTAL AREA of the vents through the roof has to be at least equal to the area of the incoming sewer line". I do not think I have installed a "full size" vent through the roof in decades, unless it was the ONLY one for the building. There is no "one answer" for the question. We would have to see a drawing for the ENTIRE plumbing system including the original venting.

 

[Asktom]

HJ, I knew you would cover my back.

I agree about the full sized vent, but it seemed to be what the poster wanted and not impractical in this case. I also agree about needing to see the whole system to give a good answer. This seems to be an addition, so, if the vents were legal before it should only be necessary to size the new ones properly by fixture units because the cross-sectional area requirement should aready have been met.

 

[hj]

The reason for seeing the entire system is that it appears he is adding two toilets, and if so, and the existing building has 2, or 3, he could have a 3" main but the additional toilers would require that it be increased to 4", which could upset the aggregate area requirement.

 

[Bill Shack]

In Quebec we required that every house have a three inch main stack that runs from the basement to the roof when it then changes to 4 inches going outside. Then the code changes to allow a reduction to 2 inches above the last bathroom connection. However we ran in to some much trouble we had to go back to the three inch all the way through to the roof.