Did I vent this correctly?

[Cl1]

Hello all,

I renovated a small 600 sq ft cottage in MA we bought ten years ago and redid the drainage and venting. At the time it was a rush job because the old cast iron was failing and I was just trying to get it habitable. I'm builder by trade and want to do it right.

I am finishing the laundry now so this is my best chance to fix anything that's wrong with it. It's a very limited space in terms of height to work with and get any kind of a stack with branches in. There is only a 6' x 6' "basement" area that you can stand up in, and the rest is crawlspace.

The fixtures served are a toilet, lav, tub, clothes washer and kitchen sink. Coming off the 4x4x3 wye with cleanout at the foundation wall I have a 3x3x1-1/2 wye that takes the tub drain, a 3x3x2 wye that takes the kitchen sink and clothes washer, a 3x3x3 wye that connects to the toilet, a 3" vent stack, and finally bushing and 1 1/2" drain running out of the picture frame that connects to the lav. All these fixtures are individually vented and tie to the 3" vent stack in the attic.

My concern is that I created a wet vent from the toilet trap arm to the vent stack connection that may not be permitted under MA code. However, that was really the only place that was feasible to get in the required full size vent stack of at least 3" running through the roof. The MA code also states "All main vents or vent stacks shall connect full size at their base to the drainage of the building or to the main soil or waste pipe, at or below the lowest fixture branch"

I don't see how I could get this to happen. I could reorient the 3" san-t vertical with a side outlet to take the lav, then continue vertically down to the level of the building drain and turn horizontal, but it would still connect upstream of the washer, tub, and kitchen sink, which would thus seem to me to not meet the code provision I quoted. Plus I would be giving up precious full height space in the basement where the water heater would ideally live.

I also want to redo the tub drain because it looks so goofy. I mocked up a 3x3x2 street wye and a 3x3x1-1/2 street wye and there is just enough room to get them in with the branches pointed straight up. The 1-1/2 one would hit the tub vent perfectly. At the time I couldn't find those street wyes anywhere hence the goofy arrangement I did was the only thing I could figure out to do.

Any and all suggestions deeply appreciated!

 

[John Gayewski]

My interpretation is that you don't have it done correctly. It would be easier to interpret a drawing. But a bathroom group can be wet vented you can't have anything draining into the wet vent that isn't the bathroom group.

 

[Sponsor]

 

[wwhitney]

This question is an exercise in definitions, but I'm not quite able to reach an answer. From MA's plumbing code (248-CMR-10), a few definitions:

Main: The principal pipe artery to which branches may be connected.
Stack: A general term for any vertical line of soil, waste, vent or inside conductor piping which extends beyond at least one branch interval in height.
Stack Vent: The portion of a soil or waste stack that is six inches above the highest flood level rim of the highest fixture connected to the stack. The stack vent terminates in compliance with 248 CMR 10.16
Vent Stack: A vertical vent pipe installed to provide circulation of air to and from the drainage system

So a vent stack is a stack that is entirely a vent, while a stack vent is the part of a combined vent and drain stack, the portion that is purely a vent.

Then 10.16(2)(a) says "All building drains within a structure shall, at minimum have at least one full size main stack vent or a vent stack no less than three inches in diameter." While the requirement referenced in the OP is 10.16(2)(c)(1) "All main vents or vent stacks shall connect full size at their base to the drainage of the building or to the main soil or waste pipe, at or below the lowest fixture branch."

So 10.16(2)(a) tells you need either a "main" stack vent or a vent stack. If you choose to have a vent stack, then 10.16(2)(c)(1) tells you where to connect it. But you could instead choose to have a main stack vent, and then 10.16(2)(c)(1) imposes no requirement on the stack vent.

Now, what does the OP have? You could say that the 3" vent that comes off the san-tee on its back in the first picture is a vent stack, but it does not comply with with 10.16(2)(c)(1).

So can we say that the OP has a stack vent? If the horizontal segment between the san-tee on its back in the first picture, and the 45 after the wye receiving the WC were not there, I would say definitely. The stack would be the 3" path from the top of the 4x4x3 wye in pictures 2 and 3, up at 45 degrees to the vertical vent that is shown in the first picture coming out of the san-tee on its back.

Now 10.16(2)(d) refers to "Offsets (in stacks) in Buildings Five or More Stories" and has various requirements that I'm not familiar with as I never consider such buildings. But it introduces the idea that a stack can have a horizontal offset, and I believe if the building is under 5 stories, there are no extra requirements placed on such a stack with a horizontal offset.

So if the OP's configuration can be construed as a stack with a horizontal offset, and as a stack vent, it complies with 10.16(2)(a) and 10.16(2)(c)(1) does not apply. But if we have to consider a vent stack, then 10.16(2)(c)(1) applies and is not satisfied.

Since I'm not very familiar with MA 248-CMR-10, I may have overlooked sections that bear on the question of whether a main stack can have a horizontal offset, or imposes further requirements on such a configuration.

Cheers, Wayne

 

[wwhitney]

All these fixtures are individually vented and tie to the 3" vent stack in the attic.

FWIW, I understand your WC to be wet vented via the lav, because the WC drain hits the 3" wye that is carrying the lav drain without any dry vent take off between the closet bend and that wye. The 3" vent through the roof that connects to the san-tee on its back can not be the vent for the WC (if say the lav drain were removed), as a horizontal dry vent takeoff and segment would not be allowed.

Except 10.16(5) on wet venting would require that the lav drain be 2" to be a wet vent, so your 1-1/2" drain doesn't work either. So I believe the WC is not properly vented.

Also, does MA require a minimum 2" dry vent for a WC? Did not notice in my perusal of 248-CMR-10.

Cheers, Wayne

 

[Cl1]

Wayne,

Thank you so much for the detailed and thoughtful response. You raise many interesting points. In my response below please note I am referencing the most recent 2023 revision of 248-CMR-10, so my section references don't match yours perfectly.

https://www.mass.gov/regulations/248-CMR-1000-uniform-state-plumbing-code

I had never considered that the horizontal piping from the toilet branch wye to the san-t might be a stack offset, but it does seem to be, according to 10.15(8)(b) "Offsets of More than 45°. A stack with an offset of more than 45° from the vertical
shall be sized as follows:
1. The portion of the stack above the offset shall be sized as for a regular stack based on the total number of fixture units above the offset.
2. The offset shall be sized as for a building drain as shown in 248 CMR 10.15(7): Table 2.
3. The portion of the stack below the offset shall be sized as for the offset or based on the total number of fixture units on the entire stack, whichever is the larger.
4. In buildings of five stories or more, a relief vent for the offset shall be installed as provided elsewhere in 248 CMR 10.16(5)(c) and in no case shall a horizontal branch connect to the offset or to the stack within two feet above or below the offset."

The horizontal section would seem to fit all those requirements. I do have the prohibited "horizontal branch connected to the offset", but that prohibition was attached to a section that applied to buildings five stories or more.

I then look at 10.16(9) Stack Venting, which states "(a)Plumbing Fixtures at the Top Interval of a Stack.
1. Plumbing fixtures at the highest level may enter into a three-inch soil or waste stack.
2. The continuations of the three-inch soil or waste stack as a vent through the roof or
re-vented into the vent system above the highest fixture shall be accepted, provided that:
a. all such fixtures shall enter said stack independently;
b. the waste pipe from all fixtures shall have a pitch of not more than 1⁄4-inch pitch
per foot;
c. the toilet and bathtub or shower drain connect to the stack at the same level; and d. the traps from all fixtures shall be placed in compliance with 248 CMR 10.16(12): Table 1."

(c) would be a problem, the tub connects at a different level.

As to wet venting, my lav drain seems to not satisfy the rules under 10.16(8) Wet Venting, which states in part (d):
"Miscellaneous Wet Venting.
1. A two inch or larger waste pipe installed with drainage fittings may serve as a wet vent.
2. The lowest portion of this horizontal pipe serving as the wet vent shall be above the top or above the center line of the horizontal drain it serves except as specifically prohibited in 248 CMR 10.16(8)(e).
3. Toilets in a bathroom below the top floor need not be individually vented if the two inch wet vented waste, serving the lavatories and bath tubs or showers connect directly to the horizontal portion of the fixture branch for the toilet by breaking the centerline or connect above the centerline of the horizontal fixture drain servicing the toilet."

The lav drain is less than 2", plus it doesn't connect to the toilet fixture branch. However, there are other examples of wet venting here and there in the MA code that are not in the wet venting section, such as 10.16(3) Prohibited Venting, which states in part (c) "Extension of Horizontal Drain. The extension or continuation of a horizontal soil or waste drain pipe shall not serve as a vent, except:
1. when permitted under wet venting 248 CMR 10.16(7); or
2. when a fixture waste of not more than two fixture units is connected to the vertical extension of the extended horizontal piping."

If my lav is an "extension of the horizontal drain", it would seem it can serve as a vent. There is no minimum size mentioned, which makes me think the normal vent sizing rules would apply, in this case that it must be at least 1/2 the size of the drain to which it connects, which it is.

None of this is very satisfying. Even with some lawyerly interpretations of what a stack is and arguing that my lav is a permissible wet vent under the "extension of the horizontal drain" bs, I have the problem that the toilet and tub connect at two different levels. If my 3" vent is a vent stack, it's connected too high. The only solution I'm seeing is to replace the san-t with a vertical san-t that has a side inlet for the lav and go straight down to the building drain (which would have to be extended a couple feet). At that point I would have a stack with no offset and my 3" vent is then clearly a stack vent and not a vent stack. My tub drain I could either connect directly to the building drain to alleviate the connecting to a stack at different levels issue, or make the 3" san tee on my stack a double side inlet and go into that at the same level as the toilet and lav. Since the stack would be moving to the left, the washer and kitchen sink would no longer be a part of it, and connect directly to the building drain.

Thoughts?

 

[wwhitney]

Stepping back for a moment, what you have appears to me to be functional and to comply with the IPC, so it would be fine in many states. Having said that, seems like it's not compliant with the MA plumbing code.

So if you are going to rip it all out and redo it, I assume that the location of the basement end of the 3" vent through the roof and of the exit to the septic are fixed. In which case the main question is what route do you take from that vent to the exit?

Seems like what would work is, starting at the vent poking down, an immediate 45 towards the exit, and then descending until you can turn horizontal (with a wye for a cleanout or just a 45) and line up with the exit. That would mean you just have a stack (with the basement portion at 45 from plumb, but that's still considered vertical) connecting to your horizontal building drain. The lav and the WC can connect to the 45 portion of the stack, in either order, as with the lav above that's a valid wet vent (even if the stack is not directly venting the lav via that connection). The tub and kitchen washing machine can join either the 45 portion of the stack, or the building drain.

Maybe that's exactly what you said at the end of your last post, and I just had to work it out for myself. : - )

Cheers, Wayne

 

[Cl1]

I agree that would satisfy the requirements to make it an uninterrupted stack with my 3" vent then being unambiguously a stack vent. But they do stress that a WC and tub need to join a stack at the same level. Am I correct in thinking a san-t with side inlet is the only fitting that could accommodate that? I'm going to draw up the only two arrangements I can come up with that seem like they would work.

 

[wwhitney]

But they do stress that a WC and tub need to join a stack at the same level.

As regards 10.16(6)(a)(2)(c) it just says "same floor level". If you look at the first picture in Example 12, it shows the shower or tub/shower hitting the stack just below the WC.

But I don't think you need to use 10.16(6) "Stack Venting" at all. Seems like either 10.16(5) Wet Venting or 10.16(7)(c) Common Vents would work for you. Stack venting allows you to vent multiple fixtures within a branch interval (story) via their trap arms connecting directly to the stack; the only fixture you would be venting via its connection to the stack would be the WC. If I understand correctly, the lav, tub, washer, and kitchen sink are all separately vented (which separate vent might reconnect to the stack vent higher up, but the point is the trap arm does not connect directly to the stack).

And if the lav drain joined the stack below the WC, then everything would be individually vented. The only reason you need to look to 10.16(5) or 10.16(7)(c) for the WC is if the lav joins the stack above the WC, as then the vent for the WC (the stack above its connection) does have drainage (from the lav) running through part of it.

So basically 10.16(6) is not a venting method you are using.

Cheers, Wayne

 

[Cl1]

As regards 10.16(6)(a)(2)(c) it just says "same floor level". If you look at the first picture in Example 12, it shows the shower or tub/shower hitting the stack just below the WC.

But I don't think you need to use 10.16(6) "Stack Venting" at all. Seems like either 10.16(5) Wet Venting or 10.16(7)(c) Common Vents would work for you. Stack venting allows you to vent multiple fixtures within a branch interval (story) via their trap arms connecting directly to the stack; the only fixture you would be venting via its connection to the stack would be the WC. If I understand correctly, the lav, tub, washer, and kitchen sink are all separately vented (which separate vent might reconnect to the stack vent higher up, but the point is the trap arm does not connect directly to the stack).

And if the lav drain joined the stack below the WC, then everything would be individually vented. The only reason you need to look to 10.16(5) or 10.16(7)(c) for the WC is if the lav joins the stack above the WC, as then the vent for the WC (the stack above its connection) does have drainage (from the lav) running through part of it.

So basically 10.16(6) is not a venting method you are using.

Cheers, Wayne

Interestingly, they did delete the word "floor" in the newest version of the code from 2023. It now says "the toilet and bathtub or shower drain connect to the stack at the same level". The previous illustration 12 has been deleted, and the illustration of stack venting now shows all tubs and WC's connecting at the same level, with a note to refer to that exact provision, now labeled 10.16(9)(a)(2)(c)

That said I agree that I could definitely wet vent the WC via the lav if it were increased in size to 2". The problem is that I still need at least one vent stack 3" or larger, but the one I have connects too high, and I just don't have anywhere else available in that wall to run it.

The two solutions I can think of are to either abandon the current lav drain and run the trap arm to the 3" vent stack, at which point I definitely have a waste stack running up into the first floor and the continuation thereof is now definitely a stack vent and not a vent stack, OR I do what you said before and 45 right off the bottom of the 3" vent in order to remove the horizontal portion and create an unambiguous and uninterrupted vertical stack with a stack vent and no vent stack.

 

[wwhitney]

Interestingly, they did delete the word "floor" in the newest version of the code from 2023. It now says "the toilet and bathtub or shower drain connect to the stack at the same level". The previous illustration 12 has been deleted, and the illustration of stack venting now shows all tubs and WC's connecting at the same level, with a note to refer to that exact provision, now labeled 10.16(9)(a)(2)(c)

What version are you looking at? I followed the link you provided in post #5 and downloaded the PDF. The document is dated 12/8/23 on the bottom of each page, and it has none of the above changes.

That said I agree that I could definitely wet vent the WC via the lav if it were increased in size to 2". The problem is that I still need at least one vent stack 3" or larger, but the one I have connects too high, and I just don't have anywhere else available in that wall to run it.

That was not my comment. I was talking about if you redid everything so that the 3" stack goes (going downstream): poke through the floor into the basement, immediate 45, then 45 to horizontal to line up with the exit through the wall. Then you have a (short) horizontal building drain and a stack. If none of the drainage connects to the stack, it is a vent stack. If some of the drainage connects to the stack, it is a stack vent. In this context, you could connect the 1-1/2" lav to the 3" WC in either order. If the lav enter above the WC, you have a short vertical wet vent that is 3" in diameter. The WC is still vented by the stack vent.

I guess you are correct that if it would be easier, you could instead just reroute the lav drain to join the stack above it's bottom. Either by moving it above the floor (but the san-tee on its back would need to become a LT90 or a combo), or by changing the san-tee on its back to a regular san-tee with side entry to receive both the WC and lav, and then putting a street LT90 out of the bottom of that. Which would lower your short horizontal section in the basement, and require you to change how the laundry/kitchen join.

So my thinking is that if you are planning to redo the tub anyway (not really necessary), as all of the above options require redoing the san-tee on its back, it's not particularly more work to redo everything in between. In which case you just need to pick the final configuration you like best, without much regard to difficulty of implementation.

Cheers, Wayne

 

[Cl1]

What version are you looking at? I followed the link you provided in post #5 and downloaded the PDF. The document is dated 12/8/23 on the bottom of each page, and it has none of the above changes.


That was not my comment. I was talking about if you redid everything so that the 3" stack goes (going downstream): poke through the floor into the basement, immediate 45, then 45 to horizontal to line up with the exit through the wall. Then you have a (short) horizontal building drain and a stack. If none of the drainage connects to the stack, it is a vent stack. If some of the drainage connects to the stack, it is a stack vent. In this context, you could connect the 1-1/2" lav to the 3" WC in either order. If the lav enter above the WC, you have a short vertical wet vent that is 3" in diameter. The WC is still vented by the stack vent.

I guess you are correct that if it would be easier, you could instead just reroute the lav drain to join the stack above it's bottom. Either by moving it above the floor (but the san-tee on its back would need to become a LT90 or a combo), or by changing the san-tee on its back to a regular san-tee with side entry to receive both the WC and lav, and then putting a street LT90 out of the bottom of that. Which would lower your short horizontal section in the basement, and require you to change how the laundry/kitchen join.

So my thinking is that if you are planning to redo the tub anyway (not really necessary), as all of the above options require redoing the san-tee on its back, it's not particularly more work to redo everything in between. In which case you just need to pick the final configuration you like best, without much regard to difficulty of implementation.

Cheers, Wayne

My goodness, you’re correct about the code version. I don’t know how it happened but somehow I downloaded an older version onto my desktop (from a ma.gov address I was sure) and all of my references and section numbers are old and yours are the correct and current ones. I’ll download the newer one with the new illustrations and re-read everything in this thread. Thanks for your help and patience!

 

[wwhitney]

yours are the correct and current ones.

For the record, not sure what version I referred to in writing posts #3 and #4, but my comments after you provided the reference in post #5 are with respect to that 12/8/23 version.

Cheers, Wayne

 

[Cl1]

Four sketches to represent existing and the three ideas I came up with:

Existing (bizzarre tub connection not shown, will be re-done regardless of anything else)

Option A (simplest and easiest to implement)

Option B

Option C (probably how I would do it if I were starting from scratch. Move lavatory drain to stack above the floor. Preserves existing WC arrangement but makes it unambiguously wet vented, with stack vent continuing through roof. More difficult now due to framing and electrical)

 

[wwhitney]

My (not very extensive) reading of the relevant MA plumbing code sections is that all 3 options comply.

My suggestion was a variant on (A), where your san-tee with additional side entry at the bottom of the vertical stack is replaced with a 45 and then a wye or san-tee with the barrel at a 45, for the WC to enter via the branch connection. The goal being to raise the start of the angled section as high as possible to reduce how much space is taken up by all the DWV.

That still leaves open how to connect the lav drain; the 45 could be instead be a wye with the barrel at a 45, so that the lav drain can 45 down into it, although given the elevation of the lav drain, that might lower the whole angled section of the stack. Or it could run past the stack and 45 down to join the building drain. Or run past and join on the angled portion of the stack by turning downward into a wye. Or the san-tee/wye for the WC could be a double fitting.

On option B, I don't see the point of the extra 4x4x3 wye. You could replace the 3x3x1-1/2 (?) wye for the tub with a double wye with the barrel still angled. Although that double wye is not available street, so not 100% sure the heights would work out.

Also you could do option B but modified the same way I suggested modifying option A.

Cheers, Wayne