Vent sizing and plumbing plan review needed

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CANXIN LEI

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I am a DIYer that building my DADU. before start drill the holes on joist , I hope get some opinion to verify the the plan is working. I don't want to destroy my floor system. except the questions, feel free to point out any other problem you find. Thank you!
I just try to reduce the holes on roof as much as i can. I don't mind to drill more holes if necessary.
UPC is used in my area.
the walls above were 2x4s.

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wwhitney

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I have not fully investigated your diagram, but I have a few preliminary comments:

- 2nd floor unit with kitchen sink, washing machine standpipe, and 2 full baths?

- Your layout appears to be horizontal wet venting the left shower and WC with the kitchen sink. That's not allowed, horizontal wet venting is limited to bathroom fixtures from one bathroom at a time. So you could wet vent the shower and WC with the lav, but not the kitchen sink. That means you'll need to provide a separate vent for the shower, and if you want that to wet vent the WC, the kitchen sink drain will need to be kept separate until downstream of the WC. Plus the vent for any WC needs to be 2", whether it is wet or dry.

- What you are calling Combi Wye I will call a combo, it's the same functionally as a wye plus street 45.

- The "90 with butt inlet" I assume is a quarter bend with low heel inlet. That is effectively a 3x2x3 sanitary tee, and so it can't be used on its back as you've drawn. You would need an upright combo. There is also a school of thought that for horizontal wet venting, the WC drain should not attach to the top of the wet vent, but should come in at the side. In which case you could use a horizontal wye or combo, with a closet bend.

- If the lav and washer standpipe are to share a vertical vent, you can do that with stacked san-tees. The lav san tee needs to be on top, with a 2" pipe section between the san-tees. The joint vent on top only needs to be 1.5".

- As far as combining vents, you can do that at an elevation of 6" above the flood rim of all the fixtures involved. A 1-1/2" vent is good for 8 DFUs (but not WCs) and a 2" vent is good for 24 DFUs. So if you were to combine (2) 1-1/2" vents with 5 DFUs each, say, the combined vent should be 2". Likewise if you combined (2) 2" vents with 13 DFUs each, the combined vent should be 3".

- Also, the aggregate vent area through the roof needs to be at least as large as the minimum size building drain. That minimum building drain size is 3" for up to 3 WCs an 35 DFUs; or 4" if either of those is exceeded.

Cheers, Wayne
 

CANXIN LEI

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I have not fully investigated your diagram, but I have a few preliminary comments:

- 2nd floor unit with kitchen sink, washing machine standpipe, and 2 full baths?

- Your layout appears to be horizontal wet venting the left shower and WC with the kitchen sink. That's not allowed, horizontal wet venting is limited to bathroom fixtures from one bathroom at a time. So you could wet vent the shower and WC with the lav, but not the kitchen sink. That means you'll need to provide a separate vent for the shower, and if you want that to wet vent the WC, the kitchen sink drain will need to be kept separate until downstream of the WC. Plus the vent for any WC needs to be 2", whether it is wet or dry.

- What you are calling Combi Wye I will call a combo, it's the same functionally as a wye plus street 45.

- The "90 with butt inlet" I assume is a quarter bend with low heel inlet. That is effectively a 3x2x3 sanitary tee, and so it can't be used on its back as you've drawn. You would need an upright combo. There is also a school of thought that for horizontal wet venting, the WC drain should not attach to the top of the wet vent, but should come in at the side. In which case you could use a horizontal wye or combo, with a closet bend.

- If the lav and washer standpipe are to share a vertical vent, you can do that with stacked san-tees. The lav san tee needs to be on top, with a 2" pipe section between the san-tees. The joint vent on top only needs to be 1.5".

- As far as combining vents, you can do that at an elevation of 6" above the flood rim of all the fixtures involved. A 1-1/2" vent is good for 8 DFUs (but not WCs) and a 2" vent is good for 24 DFUs. So if you were to combine (2) 1-1/2" vents with 5 DFUs each, say, the combined vent should be 2". Likewise if you combined (2) 2" vents with 13 DFUs each, the combined vent should be 3".

- Also, the aggregate vent area through the roof needs to be at least as large as the minimum size building drain. That minimum building drain size is 3" for up to 3 WCs an 35 DFUs; or 4" if either of those is exceeded.

Cheers, Wayne


Thank you so much for the quick reply and your info is really helpful.
I modify the plan to get a separate vent for shower and WC, I am thinking the location of E1 OR E2. Is either one of these location will fix the issue since they are dry(E1) or no up-steam fixture( E2)? or which one preferred?



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wwhitney

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E1 is not allowed for a dry vent, as a dry vent must be vertical until 6" above the flood rim of the fixture(s) served. [45 degrees off plumb is still considered vertical, so if you were able to pull the dry vent off the shower trap arm at a 45 degree angle, it could rise at that angle, but I expect you couldn't get more than 6" horizontally before the vent comes through the subfloor.]

Also, your latest drawing does not address the requirement I mentioned in my first post "if you want that to wet vent the WC, the kitchen sink drain will need to be kept separate until downstream of the WC."

Lastly, a 2" trap arm must be vented within 5' horizontally of the trap outlet, and before the trap arm falls more than 2". It also would be good (required unless you have a cleanout, perhaps?) to have less than 180 degrees of bend between the trap outlet and the vent takeoff.

Cheers, Wayne
 

CANXIN LEI

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E1 is not allowed for a dry vent, as a dry vent must be vertical until 6" above the flood rim of the fixture(s) served. [45 degrees off plumb is still considered vertical, so if you were able to pull the dry vent off the shower trap arm at a 45 degree angle, it could rise at that angle, but I expect you couldn't get more than 6" horizontally before the vent comes through the subfloor.]

Also, your latest drawing does not address the requirement I mentioned in my first post "if you want that to wet vent the WC, the kitchen sink drain will need to be kept separate until downstream of the WC."

Lastly, a 2" trap arm must be vented within 5' horizontally of the trap outlet, and before the trap arm falls more than 2". It also would be good (required unless you have a cleanout, perhaps?) to have less than 180 degrees of bend between the trap outlet and the vent takeoff.

Cheers, Wayne

So it seems like this the best way to do it? but the kitchen pipe and WC almost cover the entire living room below. I will need to focus more on the noise proofing.
Screen Shot 2021-09-19 at 9.16.47 PM.png


Also, if I want to use 3x2x3 (low heel inlet, side inlet or back inlet) on WC, Do I need to use separate vend WC (vent E and F) like picture below?
Screen Shot 2021-09-19 at 9.32.26 PM.png
Screen Shot 2021-09-19 at 9.17.07 PM.png
 
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Reach4

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So it seems like this the best way to do it? but the kitchen pipe and WC almost cover the entire living room below. I will need to focus more on the noise proofing.

Measuring Sound in PVC and Cast Iron DWV Plumbing Systems - YouTube may be of interest.

Note that they did not test ABS pipe. ABS is almost all foam core. I don't know how pvc foamcore would compare with abs foamcore for noise. I would guess they would be pretty close.

Having the pipe not in contact with the ceiling materials would seem to be best. Thicker drywall on the ceiling would add noise reduction.
 

wwhitney

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In your last post, drawing 1 still has a horizontal dry vent below the floor (shower trap arm to E2), as I've said that's not allowed.

As to the 3x2x3 low heel inlet quarter bend, it can only be used for drainage with the 2" opening pointing up. It can't be used with the 2" opening horizontal with a drain connected to it.

Cheers, Wayne
 

CANXIN LEI

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In your last post, drawing 1 still has a horizontal dry vent below the floor (shower trap arm to E2), as I've said that's not allowed.

As to the 3x2x3 low heel inlet quarter bend, it can only be used for drainage with the 2" opening pointing up. It can't be used with the 2" opening horizontal with a drain connected to it.

Cheers, Wayne
I am become confused. so the Red circle in picture is the not allowed (horizontal vent) ?
also, is the Red square (3in) can be removed because wet vent from Lav ?

1632156954.jpg
 

CANXIN LEI

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In your last post, drawing 1 still has a horizontal dry vent below the floor (shower trap arm to E2), as I've said that's not allowed.

As to the 3x2x3 low heel inlet quarter bend, it can only be used for drainage with the 2" opening pointing up. It can't be used with the 2" opening horizontal with a drain connected to it.

Cheers, Wayne
Is it able to fix by increase pipe size to 3" from WC to E2 (reduced to 2" vertical)?

Forgot to note that vent E,F,E1E2 are 90 bent vertical to attic. Not those kind of Sure-Vent
 
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wwhitney

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I am become confused. so the Red circle in picture is the not allowed (horizontal vent) ?
It's not allowed as a dry vent. It would be allowed as a wet vent, e.g. if the vertical pipe above the circle was draining a lavatory.

The idea, I think, is that with a horizontal dry vent takeoff, waste/solids can backwash into the dry vent, and material could accumulate in the vent and interfere with air flow. While a wet vent would be washed by the fixture draining into it, so nothing can accumulate. So any dry vent takeoff has to be vertical, meaning at least 45 degrees above horizontal (no more than 45 degrees from plumb).

Now to complicate things a bit more, the UPC does have an allowance for a horizontal dry vent below the fixture flood rim level if "structural conditions prohibit" having the vent rise to above the fixture flood rim. However, that allowance predates the inclusion of wet venting in the UPC, so now that wet venting is allowed, I'm not sure how that provision is being interpreted, it may not be possible to use. And it wouldn't apply to the red circle, as the dry vent takeoff still needs to be vertical--the allowance just allow it to turn back horizontal lower than otherwise allowed.

also, is the Red square (3in) can be removed because wet vent from Lav ?
Yes, if the stub up at the bottom right corner of the red rectangle is for a bathroom fixture (which includes a bathroom floor drain), and you replace the combo with a LT90.

Cheers, Wayne
 

wwhitney

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Is it able to fix by increase pipe size to 3" from WC to E2 (reduced to 2" vertical)?
No. The only way to fix it is to eliminate the horizontal dry vent. I.e. route the shower trap arm to under (or almost under, the dry vent can be up to 45 degrees off plumb) the vent location. And remember the 2" shower trap arm is limited to 5' of pipe length between the trap and the dry vent takeoff.

Cheers, Wayne
 

CANXIN LEI

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It's not allowed as a dry vent. It would be allowed as a wet vent, e.g. if the vertical pipe above the circle was draining a lavatory.

The idea, I think, is that with a horizontal dry vent takeoff, waste/solids can backwash into the dry vent, and material could accumulate in the vent and interfere with air flow. While a wet vent would be washed by the fixture draining into it, so nothing can accumulate. So any dry vent takeoff has to be vertical, meaning at least 45 degrees above horizontal (no more than 45 degrees from plumb).

Now to complicate things a bit more, the UPC does have an allowance for a horizontal dry vent below the fixture flood rim level if "structural conditions prohibit" having the vent rise to above the fixture flood rim. However, that allowance predates the inclusion of wet venting in the UPC, so now that wet venting is allowed, I'm not sure how that provision is being interpreted, it may not be possible to use. And it wouldn't apply to the red circle, as the dry vent takeoff still needs to be vertical--the allowance just allow it to turn back horizontal lower than otherwise allowed.


Yes, if the stub up at the bottom right corner of the red rectangle is for a bathroom fixture (which includes a bathroom floor drain), and you replace the combo with a LT90.

Cheers, Wayne
this very helpful. I was planned to merge the RED square to the Red Circle in wall/ceiling(for venting), now I am going to just put the 3in cleanout and cap it. Save lots of drill holes on wall. It's already pour concrete floor so no more changes below.

Regarding the red circle, the inspector was knowing it's dry vent, he corrected me to use LT90 and combo , not ST90 and Sanit Tee and then passed the inspection. He didn't mention about horizontal dry vent, that's why I am become confused. Like you said, the coding "unless prohibited by structure condition" give the authority to inspector to decide whether allowed or not?
 

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No. The only way to fix it is to eliminate the horizontal dry vent. I.e. route the shower trap arm to under (or almost under, the dry vent can be up to 45 degrees off plumb) the vent location. And remember the 2" shower trap arm is limited to 5' of pipe length between the trap and the dry vent takeoff.

Cheers, Wayne
Yes. To be safe I decide to run the pipe below the wall, so the vent just straight up.
 

wwhitney

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Regarding the red circle, the inspector was knowing it's dry vent, he corrected me to use LT90 and combo , not ST90 and Sanit Tee and then passed the inspection. He didn't mention about horizontal dry vent, that's why I am become confused. Like you said, the coding "unless prohibited by structure condition" give the authority to inspector to decide whether allowed or not?
So, a san-tee always has to be used vertically for drainage, that's why you had to change it for a combo. [If all 3 connections are vents, you can use it in other orientations.] As to the quarter bend to LT90 change, that was part of the "unless prohibited by structural conditions" clause, you need to use drainage pattern fittings when below or within 6" above the flood rim level.

But the inspector should have also told you to roll the combo up 45 degrees and put a street 45 in it to get horizontal. That way the horizontal vent below the slab is not subject to water in normal use, only during a backup. What you have under the slab will probably work fine (I would guess not worth cutting the slab to fix, not sure), but if it's convenient for you to add a cleanout on the vent riser (at least 6" above the fixture flood rim level), then you'd have access to the address the flat vent takeoff if it ever developed a problem.

Cheers< Wayne
 

CANXIN LEI

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If you post an updated drawing with your current plan, I can take another look at it sometime later today.

Cheers, Wayne

here's the most updated plan I begin to work with today.
Regarding Red square portion, i hope you can take a look for me. i am trying to draw it but it's so complicated. I will post it later if i am able to draw it.


Screen Shot 2021-09-20 at 10.20.38 PM.png
 

CANXIN LEI

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If you post an updated drawing with your current plan, I can take another look at it sometime later today.

Cheers, Wayne
Finally I found a trail software to draw. here a little background, the lower floor is below the street manhole, the inspector request to add a back-water valve, also the 2nd floor drain shall not pass the BWV.
Q1, is the Cleanout #1 (Red) located at lower floor ok?
Q2, Vent #1#3 for lower fl, #2#4 for upper fl, are they able to merge together? or has to be 2 groups (2x2" to roof)
Q3, seems like the upper shower(Red square) still have horizontal wet vent issue, is that little raiser will solve? (maybe rotate 45 + 45 bent OR straight up + short vent 90)

Thank you.

Screen Shot 2021-09-21 at 12.28.51 AM.png
Screen Shot 2021-09-21 at 12.52.46 AM.png
Screen Shot 2021-09-21 at 1.12.25 AM.png
 
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wwhitney

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1) Good question. Since you have a backwater valve, you don't want the cleanout to leak during a system backup. So I can see the argument that cleanout#1 should be above the elevation of the street manhole. On the other hand, if the threaded plug is properly tightened with dope, it would withstand 10 feet of head, meaning it would be fine.

I'm not sure about this one, whether to raise the cleanout or just be sure it's properly tightened. The relevant rules are here, I scanned them but didn't see anything directly addressing this:

https://up.codes/viewer/washington/upc-2018/chapter/7/sanitary-drainage#710.0

2) You have (3) WCs. So your building drain could be 3" (maybe it's bigger). That means the area of vents through the roof needs to be at least the area of a 3" pipe. That could be (1) 3" pipe, or (2) 2" pipes plus (1) 1.5" pipe, or (4) 1.5" pipes. Except WCs always need a 2" vent, so you will have at least one 2" vent, so (4) 1.5" pipes is not a possibility.

Vent #4 has to be 2", as it is wet venting the WC. Also, vent #2 can be 1.5", as it is only venting that lav. Not shown on the left are Vent #5, 2" for the shower and WC, and Vent #6, 1.5" for the kitchen sink.

You can combine the vents in the attic in whatever way you like that complies with the aggregate vent area rule. For example 1+2 as a 2" roof penetration, same for 3+4 and for 5+6. Or you could bring them all together and have a single 3" roof penetration.

3) That horizontal vent section is only allowed if the inspector judges that "structural conditions" preclude a fully vertical vent. In that case, the vent takeoff would be best done as a combo rolled 45 degrees off vertical, plus a 45 degree bend; or it could be a wye rolled 45 degrees off vertical, plus a 60 degree bend.

But is there no wall nearby between the shower and the WC? The best solution is just to route the shower trap arm under/next to a wall to avoid a horizontal vent section below the floor.

Cheers, Wayne
 

CANXIN LEI

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1) Good question. Since you have a backwater valve, you don't want the cleanout to leak during a system backup. So I can see the argument that cleanout#1 should be above the elevation of the street manhole. On the other hand, if the threaded plug is properly tightened with dope, it would withstand 10 feet of head, meaning it would be fine.

I'm not sure about this one, whether to raise the cleanout or just be sure it's properly tightened. The relevant rules are here, I scanned them but didn't see anything directly addressing this:

https://up.codes/viewer/washington/upc-2018/chapter/7/sanitary-drainage#710.0

2) You have (3) WCs. So your building drain could be 3" (maybe it's bigger). That means the area of vents through the roof needs to be at least the area of a 3" pipe. That could be (1) 3" pipe, or (2) 2" pipes plus (1) 1.5" pipe, or (4) 1.5" pipes. Except WCs always need a 2" vent, so you will have at least one 2" vent, so (4) 1.5" pipes is not a possibility.

Vent #4 has to be 2", as it is wet venting the WC. Also, vent #2 can be 1.5", as it is only venting that lav. Not shown on the left are Vent #5, 2" for the shower and WC, and Vent #6, 1.5" for the kitchen sink.

You can combine the vents in the attic in whatever way you like that complies with the aggregate vent area rule. For example 1+2 as a 2" roof penetration, same for 3+4 and for 5+6. Or you could bring them all together and have a single 3" roof penetration.

3) That horizontal vent section is only allowed if the inspector judges that "structural conditions" preclude a fully vertical vent. In that case, the vent takeoff would be best done as a combo rolled 45 degrees off vertical, plus a 45 degree bend; or it could be a wye rolled 45 degrees off vertical, plus a 60 degree bend.

But is there no wall nearby between the shower and the WC? The best solution is just to route the shower trap arm under/next to a wall to avoid a horizontal vent section below the floor.

Cheers, Wayne
since the clean-out already glued, i think just leave it like that until the inspector say no.

yes there's wall at the other side, it's 5'x8' standard bath. I just worry about the longer run and more bent. not sure about difference of the extra 2-3ft and additional 90 bent.

thank you so much for you information, I will posted if passed the inspection or not.
 
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