Please check my plumbing plan

[Stereo]

I would appreciate a double-check of my plumbing schematic (see crude drawing) for the addition of two 3/4 baths with a common wall. I need to keep the upper portion of the horizontal drain closer to the joists to clear a hot water heater vent connector but I then need to drop the branch to clear furnace ductwork. If I've understood wet vents correctly, the shower and lower WC will be vented via the horizontal wet vent. Please alert me to anything I have wrong. I am working under the 2018 IRC.

Many thanks for your input.

 

[Plumber69]

Here's a sloppy drawing

 

[Sponsor]

 

[Stereo]

Thanks. I was considering running the lower shower into the lower lav waste pipe as you've illustrated. It will depend on grade. I have a duct to clear which may cause the p-trap arm off the shower to be too low. It also appears that you have the upper lav draining into the upper shower arm to provide the shower with a dry vent. But in both cases, doesn't the horizontal wet vent provide the necessary air to the shower arms as long as they enter the horizontal drain line horizontally and are within the distance limits to the vent?

Also, why can't I use 1-1/2" dry vent? P3113.1 Size of Vents: "The required diameter of ... branch vents...shall be not less than one-half the required diameter of the drain served." My drain is 3". I know older code would have called for 2" dry vent, but I can't find anywhere in the 2018 code that requires anything larger than 1-1/2". My inspector OK'd 1-1/2" but he seems a bit shaky on plumbing knowledge so I would appreciate someone pointing out where 2" is required.

 

[Plumber69]

Do this then

 

[Plumber69]

Id run 1 1/2 of the last fixture and 2 inch vents off the sinks.

 

[Plumber69]

Thanks. I was considering running the lower shower into the lower lav waste pipe as you've illustrated. It will depend on grade. I have a duct to clear which may cause the p-trap arm off the shower to be too low. It also appears that you have the upper lav draining into the upper shower arm to provide the shower with a dry vent. But in both cases, doesn't the horizontal wet vent provide the necessary air to the shower arms as long as they enter the horizontal drain line horizontally and are within the distance limits to the vent?

Also, why can't I use 1-1/2" dry vent? P3113.1 Size of Vents: "The required diameter of ... branch vents...shall be not less than one-half the required diameter of the drain served." My drain is 3". I know older code would have called for 2" dry vent, but I can't find anywhere in the 2018 code that requires anything larger than 1-1/2". My inspector OK'd 1-1/2" but he seems a bit shaky on plumbing knowledge so I would appreciate someone pointing out where 2" is required.

Toilets like 2"

 

[Stereo]

I appreciate the feedback, all of which is adding dry vents. However, I am not going through the roof and don't have access to the area above the ceiling. All vents must connect to the AAV. I am still hoping someone will explain why my original plan, which uses horizontal wet vents, won't work. I understand dry vents. I have tried my best to understand wet vents from lots of reading. I believe my plan works. Please explain what's wrong with it. Thank you.

 

[Storm rider]

All vents must connect to the AAV.

You need at least one atmospheric vent. Then you MAY be able to use AAV's in some locations.

 

[Stereo]

I have 2 atmospheric vent pipes and AAV’s are allowed through the 2018 IEC to which our city conforms. The inspector confirmed that already. I am still hoping that someone will point out why my original plan with wet vent sections won’t work. It Is difficult to learn if I don’t know where, if anywhere, I’m going wrong. Thank you.

 

[James Henry]

You don't have a "wet vent" anymore, what you have is a "circuit vent with an AAV". If you have room on the higher main drain for the lav and the shower you may get away with that. The lav has to be the closest fixture to the stack.

 

[Reach4]

I am still hoping that someone will point out why my original plan with wet vent sections won’t work

If you run the lavatory drains as wet vents into the shower flow before it joins the toilet waste, everybody will be happy.

Colorado uses IPC, so I am not sure that what you drew would not be allowed if you bumped up the pipe size. But if you wet vented the showers with 2 inch from the lavatory, it makes all of the codes happy.

https://wabo.memberclicks.net/assets/pdfs/Plumbing_Venting_Brochure_2018.pdf

 

[Stereo]

I apologize for being thick-headed. I appreciate all your feedback but I am still only being shown alternates without being told what is wrong with my layout, i.e "You're plan doesn't work because..."

As I understand it, the idea of a wet vent is that the horizontal entry of the p-trap arms along the wet vent allows for air for all the fixtures entering the wet-vent section. In my layout, the 2" dry vent below the WC at the top of the line should, according to code as I understand it, provide air to the wet vent which serves the other fixtures above the vertical drop in my horizontal drain. The upper shower, being within 5' and entering the horizontal wet vent horizontally, should, according to code, receive enough air. Why do you all think that it won't?

Under "Wet Venting," the IRC says "The wet vent shall be considered to be the vent for the fixtures and shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection. Each fixture drain shall connect horizontally to the horizontal branch being wet vented or shall have a dry vent. Each wet-vented fixture drain shall connect independently to the horizontal wet vent."..."Not more than one wet-vented fixture drain shall discharge upstream of the dry-vented fixture drain connection."

James Henry, I don't understand how my plan is a circuit vent since I have vertical/wet vents on the line which are not allowed on a circuit vent. I can also find no code reference or AAV mfg installation requirement that the lav has to be the closest fixture to the stack. (And which stack are you referring to?)

If I do what is being asked of me, i.e. vertically wet-vent the upper shower with the upper lav, then I am no longer connecting each fixture drain independently to (what I believe to be) the horizontal wet vent. Instead, I'm creating side branches that are vented independently of (what I believe to be) the horizontal wet vent.

Actually, if the shower is not getting enough air, given my layout, it will be easier to dry vent the shower rather than wet vent it with the lav.


As the link Reach4 provided says, there are many entrenched ideas that provide for much more venting than has been shown to be required. I assume the 2018 code is based on the latest science so if it allows for a more efficient layout, that's my preference. However, I came to this forum because I do respect your experience. You've all seen the problems caused by bad installs. I don't want mine to be one of them. I will for sure up the vents to 2". That's easy enough to do. But I do want to understand where my plan is wrong because the other layouts will be harder to plumb.

Thank you again.

 

[James Henry]

Different venting systems were designed to accommodate different situations. You can have multiple venting systems on the same drain line. The best thing you can do is take a break, contact your building department and ask them if you can submit a sketch for your small project prior to applying for a permit. they may make minor changes to your sketch for free or for a small charge. If they won't, then I would hire someone locally who knows what would pass inspection to just consult with you. what will probably work, and what will pass as standard practice are two different things and ultimately it is up to the inspector in your jurisdiction.

 

[Stereo]

contact your building department and ask them if you can submit a sketch for your small project prior to applying for a permit.

I did get my schematic OK'd by the inspector, but as I mentioned previously, I'm not sure the inspector is any better at interpreting the code than I. Another inspector in the department with whom I was clarifying a vent termination point for a hot water heater didn't even know about one critical part of the code (and that's translated to many brand new homes in town obviously not having the required clearance from side walls). So given that my faith in our inspectors is a bit shaky, I wanted to double check with you pros.

Interestingly, I just found a recent post by you, James Henry, that seems to confirm my schematic is OK, but am I missing something?? Your post title is "Horizontal Wet Venting" dated 10/27/19. You included a link to https://www.iccsafe.org/forum/intl-plumbing-mechl-fuel-gas-codes/horizontal-wet-vent regarding code clarification. The first diagram on that iccsafe post looks very much like mine only the vent for the horizontal wet vent is provided by a vertical wet vent at a lav whereas my scheme provides a separate dry vent below the first fixture. The third post on the iccsafe post shows another diagram that is apparently used for code clarification and it appears to also be very similar to mine except for the order of fixtures . There is no lav on that second diagram and I have not found any text in the code that requires a lav to be the vent for the horizontal wet vent nor be located at any specific location along the wet vent.

I am not trying to be contrary to anyone. I REALLY appreciate your advice, but I am also a stickler for "proof." Too many years during my youth of my mother saying "just because I said so." (wink, wink)

 

[James Henry]

ultimately it is up to the inspector in your jurisdiction.

The IPC is a " base " for the local codes, every local jurisdiction doesn't have to follow it word for word, some localities don't allow the toilet to be the first fixture upstream of the wet vent on a wet vent system like you presumably have. what I discovered in that post that I previously posted, doesn't apply everywhere.

I did get my schematic OK'd by the inspector, but as I mentioned previously, I'm not sure the inspector is any better at interpreting the code than I. Another inspector in the department with whom I was clarifying a vent termination point for a hot water heater didn't even know about one critical part of the code (and that's translated to many brand new homes in town obviously not having the required clearance from side walls). So given that my faith in our inspectors is a bit shaky, I wanted to double check with you pros.

If you've already gotten your drawing approved I don't know what your trying to accomplish here. You should say to the inspector, " Thank you sir "
and start plumbing. Just because he didn't know one question doesn't mean he doesn't know the local code, its what he does for a living. Inspectors aren't perfect.

 

[Stereo]

I don't know what your trying to accomplish here."

Confirmation, given that the health of my family is at risk.

Thank you again for everyone's input.

 

[Stereo]

One more post from me regarding this topic as I hope that others seeking answers to similar questions can learn from this exchange. Us do-it-yourselfers rely heavily on information we find on the internet and much of that information is suspect, so I am still VERY open to anyone pointing out where I may be misinterpreting the 2018 IRC under which our town abides. If I'm in error, it would be very helpful to me and others to correct me. Also, as James Henry pointed out, your inspector has the last word.

Since I thought my original plan properly vented the upper shower, I have struggled to understand why commenters have encouraged me to begin the wet vent at the upper lav, then add the upper shower and then the upper WC. Perhaps it is understandable since every diagram I could find out there for wet vents starts at a lav. However, P3108.2.1 states "The dry-vent connection for a horizontal wet-vent system shall be an individual vent or a common vent for ANY [my emphasis] bathroom group fixture..." P3108.1 explains that the wet vent "...shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection." Thus, in my diagram, my wet vent runs from the 1-1/2" dry vent below the upper WC to the lower WC. (Note: Unlike some other codes, the IRC does not require that the WC be the last fixture on the wet vent.) My waste line drops vertically after the lower WC so the last two fixtures are not part of the wet vent.

Given that the upper shower with 2" trap arm is within 8' (Table P3105.2) of the wet vent, and enters the wet vent horizontally, it does not need a separate dry vent (if I and my inspector are interpreting the code correctly).

The configuration of the lower two fixtures is different than my original drawing. I was informed that this lower section of the drain could not be considered part of the upper wet vent because of the vertical drop of the main horizontal drain. In my revised plan, the lower shower will dump into the lav drain before vertically entering the main horizontal drain. The upper fixture drain from the lav is rated at 1 dfu so I only need the drain from the lav to be 1-1/2" (Table P3107.3) but I'm going to use 2" there anyway so I can use a 2x2x2 wye (+1/8 bend) at the lav drain-shower tail junction.

All the dry vents in my plan need only be 1-1/2": P3113.1 Size of vents...shall be not less than one-half the required diameter of the drain served." My drain is 3" since it serves less than 12 dfu, Table P3108.3. Keeping all vents to 1-1/2" - as allowed by my city's code - allows me to plumb in a 2 x 4 wall. That's critical for me because it allows me to keep a furnace vent in the new wall on the other side of one of the bathrooms within the wall, rather than having to box it in and have it project into the room. (I have very tight tolerances!) Plumber69 commented that toilets like 2" vents but I I'm assuming that studies have concluded that 1-1/2" works or it wouldn't be part of current code.

Again, I'm open to correction.