Too many vents (?) and acceptable wet vent sizing

[phillip_at_work]

Hello all,

I've been working up a plumbing design for my home renovation. I am not a plumber by trade (was in HVAC before attending university), but I've studied a bit and intend to install my rough plumbing consistent with Massachusetts code. I'm hoping the community might point out potential issues with my current design. To my surprise, googling "is Massachusetts IPC or UPC" returned a very confusing result.

Specific questions:
1) this design includes new fixtures on all 3 floors. Should I reduce supply water pipe diameter as I progress up the floors, to maintain pressure? What's the general guidance on this? The supply water entering the house is 3/4". The hot water heater adapts to 3/4", but immediately steps down to 1/2".
2) I believe the most efficient layout for the 3rd floor tub/shower, 2nd floor laundry, and 1st floor kitchen sink involves a wet vent. Have I sized drains the vents properly for this?
3) The main stack, as drawn, uses 3" pipe. I see conflicting resources online. Is this sufficient?
4) I draw pretty much everything with a vent. Did I overdo it?
5) The main stack is perfectly vertical, until entering the basement. Then I plan to turn it 90-deg with a wye. The basement is my woodshop and head room is paramount. Any tips for getting this assembly close to the subfloor is appreciated.

Many thanks for any feedback.

 

[John Gayewski]

Someone might want to tackle this for you, but to get all the specifics right is gonna take some research as Massachusetts had its own code which is a variant of upc.

Why are you drawing all of the piping?

Wet venting is for bathroom fixtures only. So right off the batt without looking at your drawing I can tell the research your gonna need to do well be extensive.

I suggest breaking your questions into smaller ones and using what you learn from one to inform the next.

 

[Sponsor]

 

[Reach4]

Massachusetts requires a permit. They require that only plumbers can pull plumbing permits.

You may be intending to stay under the radar.

 

[wwhitney]

0) As John commented, MA has its own code which is neither UPC nor IPC. So for a lot of these questions, you will have to check its code to get an exact answer.

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

1) No, reducing pipe diameter doesn't increase pressure. It increases pressure loss during flow, which is a negative. No upside (other than cost) to reducing the cold water pipe. The additional upside to using a smaller hot water pipe is that you wait less long for hot water, which can be important.

2) My comments on the drawings, from top down:

On the third floor at the tub and shower, you can't generally use a wye to turn a horizontal trap arm downward and simultaneously take a vent off (except for a WC). You'd need to use a double fixture fitting instead of a double wye. And the shower is generally done with a 2" trap arm; the tub trap arm could be 2" or 1-1/2" depending on what trap size you use.

Check your MA code for sizing the lav dry vent and wet vent. The UPC requires a 2" dry vent for a WC, and 2" for any horizontal wet vent, while the IPC would be OK with what you've drawn there. Not sure about MA code.

On the second floor bathroom, the double wye is fine for venting the WC as long as nothing is draining into that 3" line from the floor above. If the 3rd floor bathroom is draining in, you can't use that stack as a vent; the vents needs to rise separately and exit through the roof or reconnect to the 3" stack at least 6" above the fixture flood rim of all fixtures draining into the stack. [Unless the MA code has a section on "stack venting" in which case you might find an allowance to use the stack for venting the 2nd floor WC.]

On the second floor tub/lav, I doubt that a 1-1/2" horizontal drain is sufficient for a tub and lav, although it is in the IPC. Depending on the tub fixture drain length and fall before it connects to the lav, you may be able to eliminate the dry vent on the tub trap arm and rely on the lav to wet vent it.

You've drawn the laundry box without a trap, which is obviously wrong.

On the first floor in the powder room, your lav can wet vent the WC, but you'll need to check the sizing same as the 3rd floor.

The writing is too small to make out what is going in the kitchen. If the MA code allows AAVs, that is the simplest way to vent an island sink. If not, then you'll need to do an island loop vent, which is perhaps what you are trying to show, but what you have drawn doesn't make sense to me in plan.

3) You'll have to check the MA code on allowable number of WCs and DFUs on a 3" building drain, but mostly likely with 3 WCs 3" will suffice.

4) No, every fixture needs a vent, and I had only one suggestion above for additional wet venting.

5) To join the 1st floor power room horizontal branch drain to the stack while turning the combined drain horizontal as close to the bottom of the joists as possible, you have various options. You might want to turn the stack with a LT90 with outlet as high as possible, jog the branch drain down to the same elevation with two 45s if necessary, and then join them on the horizontal with a wye. Or if you want to join them on the vertical as shown, make the outlet of the wye at a 45 from vertical, with the stack going into the vertical branch inlet, and the WC going into the straight inlet. Could even be a street wye if you want to go directly into another wye to turn horizontal while providing a cleanout. Be sure to check the required clearances around the cleanout.

Cheers, Wayne

 

[phillip_at_work]

Hello all,

Many thanks for the feedback. Just some clarification before updating.

1) No, reducing pipe diameter doesn't increase pressure. It increases pressure loss during flow, which is a negative...

Would you suggest I run 3/4" to all fixtures, in this case? Or step down to 1/2" before piping to fixtures?

On the third floor at the tub and shower, you can't generally use a wye to turn a horizontal trap arm downward and simultaneously take a vent off (except for a WC). You'd need to use a double fixture fitting instead of a double wye. And the shower is generally done with a 2" trap arm; the tub trap arm could be 2" or 1-1/2" depending on what trap size you use.

Noted, thank you. I prefer to err on the side of caution and increase vents and drains to 2".

On the second floor bathroom, the double wye is fine for venting the WC as long as nothing is draining into that 3" line from the floor above. If the 3rd floor bathroom is draining in, you can't use that stack as a vent; the vents needs to rise separately and exit through the roof or reconnect to the 3" stack at least 6" above the fixture flood rim of all fixtures draining into the stack. [Unless the MA code has a section on "stack venting" in which case you might find an allowance to use the stack for venting the 2nd floor WC.]

Is this true for all three floors? As drawn now, the 3rd floor drains into the 2nd floor stack, which drains into the 1st floor stack. The pink colored circle denotes where the stack passes vertically through each floor. What is the proper place to connect the toilet drain from the 3rd floor? Can additional fixture venting on the 2nd floor satisfy venting requirements, allowing the 2nd floor wet vent to remain?

The writing is too small to make out what is going in the kitchen. If the MA code allows AAVs, that is the simplest way to vent an island sink. If not, then you'll need to do an island loop vent, which is perhaps what you are trying to show, but what you have drawn doesn't make sense to me in plan.

Sorry about that. I'll try to upload the next round with higher resolution. I didn't realize it was unreadable.

3) You'll have to check the MA code on allowable number of WCs and DFUs on a 3" building drain, but mostly likely with 3 WCs 3" will suffice.

Should I be looking for DFUs for a total number of fixtures? This would be 3 toilets, 3 lavs, 2 tubs, 1 shower, laundry, and kitchen sink.

5) To join the 1st floor power room horizontal branch drain to the stack while turning the combined drain horizontal as close to the bottom of the joists as possible, you have various options. You might want to turn the stack with a LT90 with outlet as high as possible, jog the branch drain down to the same elevation with two 45s if necessary, and then join them on the horizontal with a wye.

I think I'm seeing your meaning. I'll work this into the drawing on the next round.

 

[wwhitney]

Would you suggest I run 3/4" to all fixtures, in this case? Or step down to 1/2" before piping to fixtures?

I'm not suggesting that you run 3/4" to all fixtures, that would be a waste of pipe for most fixtures. You'll see almost no difference between 3/4" pipe and 1/2" pipe going to a lavatory faucet limited to 1.5 gpm, for example. I'm suggesting that just in terms of flow and pressure, there is no downside to larger pipe.

For reasons of economy, you want the minimum pipe size at every point that will carry the flow demanded of it with an acceptable frictional pressure loss due to that flow. Hitting the minimum is more important for hot water pipes than cold water pipes, because of the wait for hot water and the energy losses from stale water remaining in the pipes after you use hot water.

Is this true for all three floors?

It's true that generally a stack that receives drainage from one floor may not serve as a vent on lower floors. So in a simple layout where all the DWV is stacked vertically, you'd have a vent stack that rises from the first floor to the 3rd floor, and a separate drainage stack that falls from the 3rd floor down to the first floor. The vent stack can combine with the top of the drainage stack to a single roof penetration.

Should I be looking for DFUs for a total number of fixtures? This would be 3 toilets, 3 lavs, 2 tubs, 1 shower, laundry, and kitchen sink.

If you're talking about what to look for in the MA plumbing code, any language on minimum building drain size. The requirement would likely be phrased in terms of total number of DFUs and/or total number of water closets.

Cheers, Wayne

 

[Reach4]

Typical is to run 3/4 for cold to a bathroom and 1/2 for hot. Smaller pipe for hot lets you get hot water sooner, assuming there is not hot water recirculation.

Some run home runs to bathrooms for the same reason-- let the hot arrive sooner.

 

[phillip_at_work]

Hello all,

I'll do some more homework and post a followup drawing within the next few days. Many thanks for the feedback.

 

[phillip_at_work]

Hello all,

After some additional study, I think I have an improved drain layout. Per MA UPC, stack venting is not allowed as I drew it before. Now all 3" lines have a direct drop from their respective sources. I don't show all final vent connections in the drawing, but anywhere marked "dry vent" is understood to connect to a 3" line before exiting the roof structure.

The colored circles (green, fuchsia, cyan, and red) denote where corresponding drains pass between floors.

Any feedback is much appreciated.


1ST FLOOR

2ND FLOOR

3RD FLOOR

0TH FLOOR (BASEMENT)

 

[wwhitney]

On the san-tee at the 3rd floor lav, you must have a vent connected. The vent connection at the double fixture fitting does not vent the lav trap, as the vertical distance between the lav trap outlet and the double fixture fitting is well above the allowable 1-1/2" height difference. In fact, you could omit the vent connection on the double fixture fitting and just cap the top entry--then the lav would wet vent the WC.

Your venting of the laundry standpipe is not correct. With your A-B-C terminology on the elevation drawing, the laundry standpipe (C) trap arm gets a dry vent takeoff before the trap arm joins the drain B. That dry vent takeoff rises to at least 6" above the laundry standpipe flood rim, and then it connects to A, the vent riser from the floor below.

On the first floor half-bath, the wet venting is not correct. The 2" dry vent lav drain joins the 3" WC fixture drain before either one joins any other drainage, e.g. the 3" line coming down from the attic. That lets the lav wet vent the WC.

It is confusing that you show drainage on the first floor plan that is both in the ceiling above and the floor below. Stick with the floor below, i.e. show the drainage in the ceiling above as on the 2nd floor plan in the floor below.

Likewise with the island vent--don't show the elevation on the same drawing as the floor plan, make an inset elevation drawing like you did on the 2nd floor. Given that, no comment on the correctness of the island sink drain, but your situation is very standard, any correct island sink detail you find should apply.

On the basement plan, you don't have any fixtures, so there's no venting to deal with. I don't understand your notation about the 3x3x3x3 double fixture fitting at the top of the page where the 2" kitchen drain under the slab joins the 3" drain from above. Seems like you'd have a cleanout tee (or wye) on the vertical section of the 3" drain just before it enters the slab, and in the slab you'd have a 3x2x3 combo for the 2" horizontal drain to join the 3" vertical drain (which fitting does not exist, so you'd use a 3" combo with a 3x2 bushing in the straight inlet).

Cheers, Wayne

 

[phillip_at_work]

Hello Wayne,

On the san-tee at the 3rd floor lav, you must have a vent connected. The vent connection at the double fixture fitting does not vent the lav trap, … you could omit the vent connection on the double fixture fitting and just cap the top entry--then the lav would wet vent the WC.

Understood, thank you. I will revise away the top-most 3” vent and add a 2“ dry vent at the lav instead.

Your venting of the laundry standpipe is not correct. With your A-B-C terminology on the elevation drawing, the laundry standpipe (C) trap arm gets a dry vent takeoff before the trap arm joins the drain B. That dry vent takeoff rises to at least 6" above the laundry standpipe flood rim, and then it connects to A, the vent riser from the floor below.

I’m almost following. You’re saying I should move the vent connection up or down? From the context related to flood rim, I think maybe I should move it up at least 6” above the drain inlet.

On the first floor half-bath, the wet venting is not correct. The 2" dry vent lav drain joins the 3" WC fixture drain before either one joins any other drainage, e.g. the 3" line coming down from the attic. That lets the lav wet vent the WC.

should I join the 2” lav drain to the toilet drain, to allow the lav to wet vent the toilet?

It is confusing that you show drainage on the first floor plan that is both in the ceiling above and the floor below. Stick with the floor below, i.e. show the drainage in the ceiling above as on the 2nd floor plan in the floor below.

Likewise with the island vent--… make an inset elevation drawing like you did on the 2nd floor. …

You‘re right! Sorry about that. As I was making the notes indicating which pipe was in the floor or ceiling I realized I screwed up my conventions. I’ll revise everything to be consistent as I incorporate this next round of changes.

On the basement plan, you don't have any fixtures, so there's no venting to deal with. I don't understand your notation about the 3x3x3x3 double fixture fitting … Seems like you'd have a cleanout tee (or wye) on the vertical section of the 3" drain just before it enters the slab, and in the slab you'd have a 3x2x3 combo …

Yes, this is all what I had in mind. I slipped an extra 3 in there as a typo. I’ll add the cleanouts on the verticals, just before entering the slab, as you suggest.

Many thanks for the feedback!

 

[wwhitney]

I’m almost following. You’re saying I should move the vent connection up or down? From the context related to flood rim, I think maybe I should move it up at least 6” above the drain inlet.

The vent does not come off B and connect to A; delete the connection between B and A. The vent comes off C (i.e. off the horizontal drain between the trap and where that drain joins B) and rises to connect to A, at a sufficient height on A as previously specified.

should I join the 2” lav drain to the toilet drain, to allow the lav to wet vent the toilet?

Yes, that is what I said, and that needs to happen before either one joins the other branch drains. Then the combined drain carrying only the lav and WC can join the other branch drains.

Cheers, Wayne

 

[phillip_at_work]

Many thanks to all for feedback. Final drawings posted here for any late readers. Any glaring errors, please feel free to set me straight. Happy holidays.

 

[wwhitney]

Any glaring errors, please feel free to set me straight. Happy holidays.

Your elevation drawing for the laundry is very wrong, you created an S-trap with a horizontal dry vent below the flood rim. See below for an elevation drawing of what I described earlier.

On the island bow vent, the "relief drain" connection has to be at the lowest point of the vent side of the system. Just imagine plugging the kitchen drain at a common downstream location somewhere and filling up the drain all the way over the bow vent and thereby filling the vent pipes. Now release the downstream clog, and everything needs to drain with no trapped water in either the drain or vent.

So with your relief drain connection there, your foot vent would need to slope downward to that relief drain connection as you move from left to right on the page, and then slope upwards as you move to the right past the relief drain connection. Conventionally the relief drain connection is directly under the island, so that all of the horizontal foot vent slopes in one direction, towards the island (sloping downward to the left on the page in your diagram). Not sure if your arrangement is allowed or not by the particular wording of the MA plumbing code on island vents, you'd have to check.

Also the fitting you'd need for the relief vent connection in the location shown would be need to be a double fixture fitting with the top plugged, to get the slopes correct. Probably simpler to do it the conventional way.

Cheers, Wayne