Must Main Vent Stack attach vertically to Waste pipe?

[Jeff H Young]

Thanks wayne! dont know if ill ever get my head wrapped around the details of horrizontal wet venting .

 

[Elton Noway]

{snip}
... if you aren't going to dry vent the tub, you have to went vent the tub, and the only option I see is to use the lav drains as is typical. That makes the lav drain take a circuitous route out of the area, but that's fine.

Wayne... looks like were getting closer ... its all starting to makes sense. Thanks!

Two questions. You state "the lav drain takes a circuitous route"... Sorry afraid I need to a little clarification as I'm not sure if that statement and drawing were literal or figurative. Does the circuitous route need to be constructed as shown in your drawing (now indicated by the purple dotted line in this drawing)... or... when routing do can I simply I take the shortest route as long as the lav drain joins in where you originally indicated? (blue line from lav drain to sewer pipe only shown to clarify my question)

On another front... it appears my biggest mistake was thinking I had to include the original vent stack and failing to ask the pros in this forum before I went through all the planning and work to accomplish the relocation. All my planning on this new bathroom floor plan centered around finding a place to relocate the stack that would not interfere with any obstacles, rooms, floor or ceiling joists, etc. Was proud of myself for successfully pulling off its relocation. Part of my frustration is due to my time and energy spent in thinking a vent was required in pulling off the relocation only to have it serve as a lav vent which could have been wet vented. This takes me back to an earlier question. Could I have just capped off the 3" pipe on the roof and planned this entire project without any vent stack at all? I'm confused because every house I've ever lived in (all older ones) have always had one or two vent stacks. I'll have to pay closer attention to some newer homes next time I'm out driving around.

 

[Sponsor]

 

[Elton Noway]

why not offset the main back a ways and come up in the "new vent location" and pick up shower and w/c from there ? and perhaps using a wye where doing that offset picking up the lavs and tub off a 2 inch branch or bushing down a 3 inch wye to continue to lavs and tub. Sorry I know Im not real clear . Id kinda like to use that 3 inch vent if its easy.
Wayne probebly brainstorming up something good LOL !

Hi Jeff... When you say "offset the main back a ways" ... need some clarification. Do you mean cutting into the 4" sewer main and reroute the portion that falls under the bathroom so would be located on the other side of the main beam? (Obviously the entire "octopus" at the clean out end is going away since its all the old / original drain system)

 

[wwhitney]

Two questions. You state "the lav drain takes a circuitous route"... Sorry afraid I need to a little clarification as I'm not sure if that statement and drawing were literal or figurative.

Primarily figurative. I wouldn't advise the particular diagonal route you drew. But you could cut off most of the corner by using two 45s.

Could I have just capped off the 3" pipe on the roof and planned this entire project without any vent stack at all?

I answered this question earlier: "Both your lavs will be need to be dry-vented, so those vent(s) will need to connect to your existing roof penetration. It's just that you don't need a 3" dry vent that goes all the way from the 3" / 4" drain below the floor up through the roof."

Cheers, Wayne

 

[Jeff H Young]

Actualy I like waynes wet vent plan . you can rework the old 3 inch vent . and tie your dry vents into it from the lavs

 

[Elton Noway]

Primarily figurative. I wouldn't advise the particular diagonal route you drew. But you could cut off most of the corner by using two 45s.

I answered this question earlier: "Both your lavs will be need to be dry-vented, so those vent(s) will need to connect to your existing roof penetration. It's just that you don't need a 3" dry vent that goes all the way from the 3" / 4" drain below the floor up through the roof."

Cheers, Wayne

Sorry... I'm still here... been tied up under the house replacing cracked floor joists. Thanks for responses Wayne. Much appreciated. Just like patients questioning their doctors after spending too much time on WebMD... not being in the trade nor understanding all the complexities I was hung up on the idea that a toilet required its own dedicated vent. Confusing me further was the myriad of diagrams on the internet showing a vent next to the toilet and the assortment of horror stories with sewer gas problems because the toilet was installed downstream of the tub or shower an not vented correctly. In any event I believe I'm back on track

If I may... back to your earlier reply where you commented on venting the tub and the partition wall.

... {snip}...

Comments: the tricky part is venting the tub. For a dry vent, you indicated the top and left walls (on the page) are out. So the only option would be if you add that potential partition wall and use it to dry vent the tub. Which would be a fine option (easy for me to draw out) if you desire to have a solid wall there, but I wouldn't say it's a reason to use a partition wall there instead of glass if you prefer glass.

I ran the partition wall idea by the wife and shes in favor of "less glass" from a maintenance / cleaning perspective. If its not too much trouble you mentioned you could draw out the plumbing with the solid partition wall option. No hurry... enjoy whats left of the weekend. I still have to finish the subfloor repairs before I start plumbing. I attached two versions of the drawing... one with your most recent layout suggestions and one without if you need a blank canvas.

 

[wwhitney]

OK, below is an option that is closest to your original vertical design. [3" = orange, 2" = blue, 1-1/2" = green.] You have a 3" stack at the specified location. It dry vents the WC and the shower, because the shower is close enough and the WC has no distance limit from its vent (under the IPC). The shower needs to connect to the the stack above the WC.

But the tub and the lav are too far from the 3" stack to be vented by it. So they each get a separate 1-1/2" dry vent, represented by the green circles shown. Those dry vents have to rise to at least 6" above the fixture flood rims before going horizontal or connecting to the vent portion of the 3" stack. Connecting within the ceiling framing or attic is often a good option.

The elevation of the lav and shower drains connecting to the 3" stack is unregulated, because they are already vented, so they don't depend on the stack for venting (unlike the shower); and as non-WC bathroom fixtures, their connection to the stack wouldn't disrupt the venting the of the shower. [If the shower is topmost connection, then it is dry-vented; if the lav and/or tub drain connects above, then it is vertically wet vented; either way is fine.]

Now the drain for the 2 lavs is not serving as a wet vent for anything, so the IPC allows a 1-1/2" drain to carry 2 lavs. But if you want to use a double fixture fitting to take two lav trap arms off a single lav stack, then you'd need to use 2" for the drain carrying both lavs, as I'm not aware of a 1-1/2 x 1-1/2 x 1-1/2 x 1-1/2 double fixture fitting.

Cheers, Wayne

 

[Jeff H Young]

This last drawing is something like I had in mind , I was thinking offseting farther back and going straight at the vent location but little differance if its on a 45 or going straight I dont know where shower valve is going but lets keep that 3 or 4 inch stack clear of it .

 

[Elton Noway]

OK, below is an option that is closest to your original vertical design. [3" = orange, 2" = blue, 1-1/2" = green.] You have a 3" stack at the specified location. It dry vents the WC and the shower, because the shower is close enough and the WC has no distance limit from its vent (under the IPC). The shower needs to connect to the the stack above the WC.

But the tub and the lav are too far from the 3" stack to be vented by it. So they each get a separate 1-1/2" dry vent, represented by the green circles shown. Those dry vents have to rise to at least 6" above the fixture flood rims before going horizontal or connecting to the vent portion of the 3" stack. Connecting within the ceiling framing or attic is often a good option.

The elevation of the lav and shower drains connecting to the 3" stack is unregulated, because they are already vented, so they don't depend on the stack for venting (unlike the shower); and as non-WC bathroom fixtures, their connection to the stack wouldn't disrupt the venting the of the shower. [If the shower is topmost connection, then it is dry-vented; if the lav and/or tub drain connects above, then it is vertically wet vented; either way is fine.]

Now the drain for the 2 lavs is not serving as a wet vent for anything, so the IPC allows a 1-1/2" drain to carry 2 lavs. But if you want to use a double fixture fitting to take two lav trap arms off a single lav stack, then you'd need to use 2" for the drain carrying both lavs, as I'm not aware of a 1-1/2 x 1-1/2 x 1-1/2 x 1-1/2 double fixture fitting.

Cheers, Wayne

Great! Thanks Wayne. It all makes sense. As you might guess I have a question. As long as I maintain the correct slopes and tie in all the various drains as you indicated in your instructions... does it make a difference "where the the new vertical design stack is located? Here's the deal: The new stack location enters the crawl 30" from the main sewer line. Should I assemble the stack (i.e. octopus) directly under the new stack location then use an angled 3" pipe to exit the bottom of the stack and angle it over where I would tie it into the existing drain?... or... Since its a dry vent, could I put a 90 on the new stack after it enters the crawl just below the joists, add 30 " of pipe (slightly sloped) at an angle so it falls somewhere along the center axis of the main drain (dotted lines in photo) , then assemble the stack vertically directly over the main sewer? The reason for asking is although the new vent location works great for everything above the crawl space but where it enters the crawl gets a little crowded, about a foot from a hard HVAC plenum and a 18" flexible duct. Not that assembling the stack in the area is impossible, just less elbow room.
Or... was the idea for me to move the 4" main to the other side of the main beam and go straight at the new vent location? If I cut and move that section of the 4"" main I'll have to tie it back it to the rest of the line (assuming a couple 45's is not a problem).
Sorry for all the questions

 

[wwhitney]

Should I assemble the stack (i.e. octopus) directly under the new stack location then use an angled 3" pipe to exit the bottom of the stack and angle it over where I would tie it into the existing drain?

Yes, under that plan.

... or... Since its a dry vent, could I put a 90 on the new stack after it enters the crawl just below the joists, add 30 " of pipe (slightly sloped) at an angle so it falls somewhere along the center axis of the main drain (dotted lines in photo) , then assemble the stack vertically directly over the main sewer?

No. The portion of the DWV above the highest drain entry to this vertical configuration is a dry vent. And dry vents have to stay vertical until at least 6" above the fixture flood rim. So you can't offset the dry vent under the floor like that.

Or... was the idea for me to move the 4" main to the other side of the main beam and go straight at the new vent location? If I cut and move that section of the 4"" main I'll have to tie it back it to the rest of the line (assuming a couple 45's is not a problem).

For that design, the 3" pipe outside the footprint of the bathroom would presumably be close to the elevation of your existing 4" building drain, since you'd be coming out the bottom of the vertical configuration with a long turn 90.

If the vicinity of the proposed 3" stack is crowded, I don't see much upside to actually having a 3" stack, so you may wish to consider the following horizontally wet vented configuration. The tub drain gets dry vented and wet vents the WC and shower. All the piping shown would be close to the underside of the joists, and not shown would be a vertical drop (via two 45s or two 90s) to connect to your 4" building drain. [Actually the building drain connection should maybe be via a wye or combo, so that you can extend the 4" drain a bit upstream to a cleanout.]

Cheers, Wayne

 

[Elton Noway]

Okay... Thanks Wayne... I certainly can't say you haven't given me a myriad of options to consider. I guess I was thinking I had room between the main drain and the bottom of the floor joists to introduce the new vent stack "with" a 3" 90 but looking at it now I can see it would be near impossible without all the right components. I certainly appreciate all your time, expert help and guidance! You're the best!



UPDATE: I went back to the beginning and re-read every post and line. Part of my initial problem was thinking that drains and vents were both physically different lines and by not fully understanding wet venting where the "drain" also serves as the vent.

I also screwed up in one of my responses where I indicated the top and left walls were out for vent/drain consideration. The top wall is fine, only the left wall is out. I wanted to mention this only because you replied:"
"the tricky part is venting the tub. For a dry vent, you indicated the top and left walls (on the page) are out. So the only option would be if you add that potential partition wall and use it to dry vent the tub."

Below is the drawing you originally submitted when you made the above response (#20). Since all the drains are all below floor I've been struggling trying to envision your idea and how utilizing the top wall might have been a better option. Was wondering if you were going to tie into the 1 1/2" overhead vent line shown in my first post. No need to draw out another plan... (I feel bad already) If you could just tell me your idea I'll try to fill in the gaps... then will bow out with my tail between my legs.
.

 

[Jeff H Young]

Not knowing how youll be dealing with the vent stack. but if I went with waynes drawing above . I might concider taking out the shower drain and trap and adding a 4x4x3 combi to run over to the new vent location and on top of the 90 going up the wall install a 3x3x2 santee pointed toward shower drain location short piece of pipe and p trap.
Some of the codes get a bit confusing on reducing vent pipe sizes not sure what they require but Im sure this will be legal on the vent. I dont know either how you were planning to adress it or if your code does or does not still require a 3 inch vent undiminished in size . I dont want to make more work for you so if you are sure the vent issue is resolved then forget my idea

 

[Elton Noway]

Not knowing how youll be dealing with the vent stack. but if I went with waynes drawing above . I might concider taking out the shower drain and trap and adding a 4x4x3 combi to run over to the new vent location and on top of the 90 going up the wall install a 3x3x2 santee pointed toward shower drain location short piece of pipe and p trap.
Some of the codes get a bit confusing on reducing vent pipe sizes not sure what they require but Im sure this will be legal on the vent. I dont know either how you were planning to adress it or if your code does or does not still require a 3 inch vent undiminished in size . I dont want to make more work for you so if you are sure the vent issue is resolved then forget my idea

Hi Jeff...Thanks for the input. As I'm quickly discovering... there's more than one way to skin a cat. Not that there was a issue as much as me hoping to complete two objectives 1) Make sure all the fixtures were plumbed and vented to IPC requirements 2) Include the homes original 3' vent stack somewhere in the redesign. (only because I went thru great lengths to design and plan the bathroom around the stack, even though I've since discovered the stack isn't even necessary) Your suggestion makes perfect sense as well but I don't have a clue if reducing the vent size will still be compliant. Will research later today.

 

[Jeff H Young]

I was looking at 904.1 but it was older code and we use UPC in Ca you are IPC based . I think wayne said its not required but if not required im still not so sure that 3 inch can be reduced down to 1 1/2 " or if you are entirely re plumbing entire system.

 

[wwhitney]

UPDATE:

I don't get a notification when you edit your existing post, so updates are best made in a new post.

Cheers, Wayne

 

[wwhitney]

The main requirement in the IPC for vent sizing is that a vent must be 1/2 the diameter of the minimum required drain diameter. 904.1 does require a vent through the roof that is at least as large as 1/2 the diameter of the required building drain size (the drain size for all the fixtures in a building).

2018 INTERNATIONAL PLUMBING CODE (IPC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.

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The IPC allows 42 DFU (drainage fixture units) on a 3" building drain sloped at 1/4" per foot. So a house with 42 DFUs or less is OK with a 1-1/2" vent through the roof. If the numbers of DFUs exceeds the limit of a 3" building drain, then you will need a 2" vent through the roof.

2018 INTERNATIONAL PLUMBING CODE (IPC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.

codes.iccsafe.org

However, NC has amended those sections of the IPC. It limits a 3" building drain to 3 WCs total, via Footnote c to Table 710.1(1)

Chapter 7 Sanitary Drainage: Sanitary Drainage, 2018 North Carolina Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

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Moreover, NC has amended 904.1 to require a minimum 2" vent through the roof. And 904.1.1 says that 2" vent must connect to the building drain or a branch thereof that is at least 3" in diameter.

Chapter 9 Vents: Vents, 2018 North Carolina Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

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That last part is news to me, and so the question is whether the 4" building drain that extends off the page to the right has any other stacks connected to it that have a 2" vent through the roof?

If not, then the bathroom layout needs to be adjusted to add a minimum 2" dry vent to the 3" WC line. That's not hard to do; the layout in post #27 does that already. To decongest that area labeled "new vent stack location" that has the rigid air return ducting right next to it, the separately vented lav and tub drains could be rerouted to join the 3" branch or 4" building drain downstream.

Cheers, Wayne

 

[Elton Noway]

The main requirement in the IPC for vent sizing is that a vent must be 1/2 the diameter of the minimum required drain diameter. 904.1 does require a vent through the roof that is at least as large as 1/2 the diameter of the required building drain size (the drain size for all the fixtures in a building).

2018 INTERNATIONAL PLUMBING CODE (IPC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.

codes.iccsafe.org

The IPC allows 42 DFU (drainage fixture units) on a 3" building drain sloped at 1/4" per foot. So a house with 42 DFUs or less is OK with a 1-1/2" vent through the roof. If the numbers of DFUs exceeds the limit of a 3" building drain, then you will need a 2" vent through the roof.

2018 INTERNATIONAL PLUMBING CODE (IPC) | ICC DIGITAL CODES

ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.

codes.iccsafe.org

However, NC has amended those sections of the IPC. It limits a 3" building drain to 3 WCs total, via Footnote c to Table 710.1(1)

Chapter 7 Sanitary Drainage: Sanitary Drainage, 2018 North Carolina Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Moreover, NC has amended 904.1 to require a minimum 2" vent through the roof. And 904.1.1 says that 2" vent must connect to the building drain or a branch thereof that is at least 3" in diameter.

Chapter 9 Vents: Vents, 2018 North Carolina Plumbing Code | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

That last part is news to me, and so the question is whether the 4" building drain that extends off the page to the right has any other stacks connected to it that have a 2" vent through the roof?

If not, then the bathroom layout needs to be adjusted to add a minimum 2" dry vent to the 3" WC line. That's not hard to do; the layout in post #27 does that already. To decongest that area labeled "new vent stack location" that has the rigid air return ducting right next to it, the separately vented lav and tub drains could be rerouted to join the 3" branch or 4" building drain downstream.

Cheers, Wayne

Hi Wayne, thanks for the additional info. At a quick glance and trying to decipher the individual requirements it "appears" my house might be compliant as built. The house has a 4" main that runs its entire length with a 3" vent thru the roof that initially joins the 4" main at the far upstream end. The house has 3 W/C's, each entering the main drain via a 3" branch. In addition to the 3" master bath roof vent we've been discussing... it also has one 2" roof vent coming up from a second full bath lav, a 1 1/2 roof vent coming up from the laundry room washing machine drain, and 1 1/2" roof vent coming of a lav in a third bathroom. How each vent is actually routed within the walls is anybodys guess. On a side note: per my calculations my house DFU is 28.

 

[wwhitney]

it also has one 2" roof vent coming up from a second full bath lav

If that path from the roof down to the building drain consists of a 2" dry vent connecting to a 3" drain stack connecting to the 4" building drain, then if I understand NC's amendments correctly (not sure), that would take care of compliance with them. In which case you don't need to try to comply with a 2" or 3" vent stack in the bathroom you are working on.

Or you could play it safe and try to comply with this bathroom. I.e. pull a 2" dry vent off the 3" WC drain line, rather than wet venting it via the tub.

Cheers, Wayne

 

[Elton Noway]

If that path from the roof down to the building drain consists of a 2" dry vent connecting to a 3" drain stack connecting to the 4" building drain, then if I understand NC's amendments correctly (not sure), that would take care of compliance with them. In which case you don't need to try to comply with a 2" or 3" vent stack in the bathroom you are working on.

Or you could play it safe and try to comply with this bathroom. I.e. pull a 2" dry vent off the 3" WC drain line, rather than wet venting it via the tub.

Cheers, Wayne

Makes sense... thank you! Of all your designs I plan on going with your layout from post #27.

Question: As you know this layout utilizes a partition wall between to toilet and shower which was a consideration after I "incorrectly" stated the left and top walls of the drawing were not available for consideration in your plumbing designs. Actually there is a four foot section on the far left of the top wall that could be utilized, which raises a question.

The "original" 1 1/2" lav vent ran up the lav wall and above the ceiling and up again where it eventually ties into the 3" stack in the attic. I made no change to that layout other than moving it to the right so it now falls over the new lav wall. So... rather than using a partition wall between the toilet and shower to dry vent the tub ... could I tie another 1 1/2 vent line into the existing 3" stack up in the attic and run it down into the crawl space via the four foot section indicated by the green dotted lines in the photo... and if so, where would I tie it in?

 

[wwhitney]

Again, dry vents have to come off a trap arm vertically and rise vertically until at least 6" above the fixture flood rim level.

So if you want to use a dry vent riser in the portion of the wall you outlined in dashed purple, you would need to reroute the tub trap arm to travel under or next to that wall. 45 degrees from plumb is still considered vertical, so if the tub trap arm is next to the wall, the dry vent could come off it and rise at a 45 to get under the wall plate and turn up into the wall. With your drains under the floor joists, the dry vent could offset around 12" laterally while rising around 12" below the subfloor. The tub drain routing would be a bit circuitous in the end.

Or just as good, since you said the lefthand (on the page) wall is also a possibility for venting, you could put a dry vent in there, between the tub and WC. For that I'd suggest shooting the trap arm coming out of the trap straight toward the plan location of your dry vent, hitting a san-tee in the usual vertical configuration for the vent takeoff, and then having the drain outlet of the san-tee immediately hit a LT90 to turn horizontal, pointed back towards the right side of the plan. (* see below for a variation)

So those are your options for venting the tub: wet vent by rerouting the lav drain, or dry vent in the shower wall, in the portion of the wall on the top of the page, or in the wall on the left side of the page.

Cheers, Wayne

(*) a variation on that is to bring the vent riser through the floor in the knee wall, and then have the vent rise to the left at a 45 to enter the lefthand wall below the top of the kneewall. [Or if the kneewall is at least 12" taller than the tub flood rim, you would have room for the vent to rise vertically to a 90 that is 6" above the tub flood rim but still within the knee wall.] This would let you point the tub trap outlet up the page, turn the trap arm to the the right with a LT90, and then take off the vent with an upright combo. That avoids the elevation drop from using a san-tee and LT90, which I suggested because you would need the trap arm to do a 180.