Venting side by side bathrooms, and another bathroom a floor below

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Tudorrenovator

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Working on a 100 year old home, have removed the cast iron and am replacing with PVC. I am limited by the existing structure hence some of the quirks.

There are 2 full baths on the second floor, side by side, on a 3” line with a 3” vent in the middle going to the roof. All the fixtures are venting though the 3” drain line. Can I wet vent both bathrooms on the 3” horizontal using the 3” roof vent?

Also, there is a powder room on the first floor below, with the toilet and sink going separately to the 4” main stack in the basement. Will those vent ok through the 3” roof vent?
 

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wwhitney

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I did not completely decipher your diagram as its layout is non standard. But I gather that in the vicinity of a 2 story 3" stack (no fixtures above the 2nd story), you have upstairs 2 full baths (lav, WC, tub) and downstairs 1 half bath (lav, WC).

Then the standard IPC wet venting arrangement would require 3 dry vent connections, one at each lav. These dry vents would rise to at least 6" above the upper story lav flood rims and then could reconnect to the stack. In particular the downstairs lav vent has to rise up to the 2nd story separate from the stack. Or under the IPC you could use an AAV at that lav.

Then each lav can wet vent the fixtures within its bathroom, by having the lav drain join the WC drain or tub drain first, and then the branch drain joining the other fixture (if present) before hitting the stack. For the tubs, the tub trap arm will be from the trap outlet to the wye where it joins the (wet venting) branch drain, and that trap arm can fall no more than one pipe diameter.

However, the IPC does have an allowance for a "waste stack vent" where the multi-story stack provides venting for the downstairs fixtures even though the upstairs fixtures are draining through it. IIRC it is based on a practice that is common in the area around Philadelphia. So if you are interested in that option to avoid running a separate vent between floors for the downstairs half-bath, you can read the code requirements here:


Cheers, Wayne
 

John Gayewski

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Your drawing is showing plan and elevation views mixed together? If so is kind of unknowable of what you have is legal. The lavs should vent the bathroom groups seperately and then come back to the 3" vent at 42" above the floor.

You can't wet vent between floors. The lower fixtures need vents that also merge into the 3 vent through roof.
 

Tudorrenovator

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I did not completely decipher your diagram as its layout is non standard. But I gather that in the vicinity of a 2 story 3" stack (no fixtures above the 2nd story), you have upstairs 2 full baths (lav, WC, tub) and downstairs 1 half bath (lav, WC).

Then the standard IPC wet venting arrangement would require 3 dry vent connections, one at each lav. These dry vents would rise to at least 6" above the upper story lav flood rims and then could reconnect to the stack. In particular the downstairs lav vent has to rise up to the 2nd story separate from the stack. Or under the IPC you could use an AAV at that lav.

Then each lav can wet vent the fixtures within its bathroom, by having the lav drain join the WC drain or tub drain first, and then the branch drain joining the other fixture (if present) before hitting the stack. For the tubs, the tub trap arm will be from the trap outlet to the wye where it joins the (wet venting) branch drain, and that trap arm can fall no more than one pipe diameter.

However, the IPC does have an allowance for a "waste stack vent" where the multi-story stack provides venting for the downstairs fixtures even though the upstairs fixtures are draining through it. IIRC it is based on a practice that is common in the area around Philadelphia. So if you are interested in that option to avoid running a separate vent between floors for the downstairs half-bath, you can read the code requirements here:


Cheers, Wayne
Great input thank you so much. Yes this is Philly area.
I did not completely decipher your diagram as its layout is non standard. But I gather that in the vicinity of a 2 story 3" stack (no fixtures above the 2nd story), you have upstairs 2 full baths (lav, WC, tub) and downstairs 1 half bath (lav, WC).

Then the standard IPC wet venting arrangement would require 3 dry vent connections, one at each lav. These dry vents would rise to at least 6" above the upper story lav flood rims and then could reconnect to the stack. In particular the downstairs lav vent has to rise up to the 2nd story separate from the stack. Or under the IPC you could use an AAV at that lav.

Then each lav can wet vent the fixtures within its bathroom, by having the lav drain join the WC drain or tub drain first, and then the branch drain joining the other fixture (if present) before hitting the stack. For the tubs, the tub trap arm will be from the trap outlet to the wye where it joins the (wet venting) branch drain, and that trap arm can fall no more than one pipe diameter.

However, the IPC does have an allowance for a "waste stack vent" where the multi-story stack provides venting for the downstairs fixtures even though the upstairs fixtures are draining through it. IIRC it is based on a practice that is common in the area around Philadelphia. So if you are interested in that option to avoid running a separate vent between floors for the downstairs half-bath, you can read the code requirements here:


Cheers, Wayne
I did not completely decipher your diagram as its layout is non standard. But I gather that in the vicinity of a 2 story 3" stack (no fixtures above the 2nd story), you have upstairs 2 full baths (lav, WC, tub) and downstairs 1 half bath (lav, WC).

Then the standard IPC wet venting arrangement would require 3 dry vent connections, one at each lav. These dry vents would rise to at least 6" above the upper story lav flood rims and then could reconnect to the stack. In particular the downstairs lav vent has to rise up to the 2nd story separate from the stack. Or under the IPC you could use an AAV at that lav.

Then each lav can wet vent the fixtures within its bathroom, by having the lav drain join the WC drain or tub drain first, and then the branch drain joining the other fixture (if present) before hitting the stack. For the tubs, the tub trap arm will be from the trap outlet to the wye where it joins the (wet venting) branch drain, and that trap arm can fall no more than one pipe diameter.

However, the IPC does have an allowance for a "waste stack vent" where the multi-story stack provides venting for the downstairs fixtures even though the upstairs fixtures are draining through it. IIRC it is based on a practice that is common in the area around Philadelphia. So if you are interested in that option to avoid running a separate vent between floors for the downstairs half-bath, you can read the code requirements here:


Cheers, Wayne
Thank you- that section says: The stack shall not receive the discharge of water closets or urinals.

Does this mean toilets can’t tap into the vertical waste/vent stack? I have seen that many times so wasn’t sure if I was misinterpreting it?
 

wwhitney

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Thank you- that section says: The stack shall not receive the discharge of closets or urinals.
Oops, that was the wrong section, I meant IPC 917:


Cheers, Wayne
 

Tudorrenovator

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Your drawing is showing plan and elevation views mixed together? If so is kind of unknowable of what you have is legal. The lavs should vent the bathroom groups seperately and then come back to the 3" vent at 42" above the floor.

You can't wet vent between floors. The lower fixtures need vents that also merge into the 3 vent through roof.
Can the two 2nd floor bathrooms wet vent through the 3” horizontal drain (that connects to the 3” roof vent) without the lav dry vents?

For the 1/2 bath, I would need to revent from there above the flood line on the 2nd floor and tie into the vent stack there?
 

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Oops, that was the wrong section, I meant IPC 917:


Cheers, Wayne
Thanks for that- it states A 3-inch (76 mm) stack shall serve not more than two water closets.

Since the 1/2 bath is draining into a 4” pipe, would ther be sufficient or do I need to size the stack and the vent to 4” to accommodate all the bathrooms?
 

wwhitney

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Thanks for that- it states A 3-inch (76 mm) stack shall serve not more than two water closets.

Since the 1/2 bath is draining into a 4” pipe, would ther be sufficient or do I need to size the stack and the vent to 4” to accommodate all the bathrooms?
If you read the full section you quoted (917.2) it says the whole stack and vent have to be same size. So it sounds like 4" would be required throughout for IPC917.

Also see 917.7 on horizontal offsets in the stack which from your diagram I think would apply.

Sounds like conventional wet venting would be easier if it's not crazy difficult to add the 3 lav revents.

Cheers, Wayne
 

Tudorrenovator

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If you read the full section you quoted (917.2) it says the whole stack and vent have to be same size. So it sounds like 4" would be required throughout for IPC917.

Also see 917.7 on horizontal offsets in the stack which from your diagram I think would apply.

Sounds like conventional wet venting would be easier if it's not crazy difficult to add the 3 lav revents.

Cheers, Wayne
The challenge is the lav wont be in the first position, the structure of the building is usually toilet, lav, tub. Can I dry vent if the lav is after the toilet?
 

Terry

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dwv_b2.jpg

Vented normally.

dwv_b1.jpg


Wet vented.

I don't know of a plumbing code that allows wet venting between floors. It seems like a very bad idea, as air coming down the line can push water out of traps and toilet bowls.
 

Tudorrenovator

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dwv_b2.jpg

Vented normally.

dwv_b1.jpg


Wet vented.

I don't know of a plumbing code that allows wet venting between floors. It seems like a very bad idea, as air coming down the line can push water out of traps and toilet bowls.
Thanks Terry, love the site. Could I have both top floor bedrooms wet vent into the 3” horizontal with the vent located in the middle? They are back to back bathrooms.

Would the above work if I revent the 1/2 bath to the 2nd floor vent stack? Meaning, is the issue the powder room on the floor below?
 

wwhitney

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The challenge is the lav wont be in the first position, the structure of the building is usually toilet, lav, tub. Can I dry vent if the lav is after the toilet?
From the point of view of the plumbing pipes, there's no distinguishing first (upstream-most) and second fixtures. All that you can distinguish is the first joint, the upstream most wye.

Horizontal wet venting just requires the lav to be one of those two upstream most fixtures, that feed into the upstream most wye. I.e. you can't have the tub and the WC join together, and then the lav join in third.

So going by decreasing distance from the stack, WC (farthest), then lav, then tub, not a problem.

Cheers, Wayne
 

Tudorrenovator

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From the point of view of the plumbing pipes, there's no distinguishing first (upstream-most) and second fixtures. All that you can distinguish is the first joint, the upstream most wye.

Horizontal wet venting just requires the lav to be one of those two upstream most fixtures, that feed into the upstream most wye. I.e. you can't have the tub and the WC join together, and then the lav join in third.

So going by decreasing distance from the stack, WC (farthest), then lav, then tub, not a problem.

Cheers, Wayne
From the point of view of the plumbing pipes, there's no distinguishing first (upstream-most) and second fixtures. All that you can distinguish is the first joint, the upstream most wye.

Horizontal wet venting just requires the lav to be one of those two upstream most fixtures, that feed into the upstream most wye. I.e. you can't have the tub and the WC join together, and then the lav join in third.

So going by decreasing distance from the stack, WC (farthest), then lav, then tub, not a problem.

Cheers, Wayne
So basically the vent needs to be behind the flow of the waste? Or is that oversimplified. Really appreciate the input. If this was a new build it would be much easier, it’s a historic house so I’m trying not to tear out all the tiles/floors/walls and space is very limited.
 

wwhitney

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So basically the vent needs to be behind the flow of the waste? Or is that oversimplified.
I'd say oversimplified. : - )

The fixture's vent connection, whether wet or dry, needs to be (with one exception in the IPC) before or as the fixture's drain connects to another drain. In the case of wet venting, it has to be as the fixture's drain connects to the drain that is providing the wet vent.

So what you can't do is join the WC drain to the tub drain, and then join that to dry-vented lav drain, and expect the lav to wet vent both the WC drain and the tub drain. The vents for the WC and tub would need to be at that joint, not downstream where the lav comes in.

But if you joint the dry-vented lav fixture drain (= only one fixture) to the tub fixture drain (within the trap arm limits), and have the lav wet vent the tub. Then that branch (= more than one fixture) can join the WC fixture drain and wet vent the WC. And for the IPC, that order (tub first, then WC) is not required the lav could hit the WC first, then the tub.

Cheers, Wayne
 

Tudorrenovator

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I'd say oversimplified. : - )

The fixture's vent connection, whether wet or dry, needs to be (with one exception in the IPC) before or as the fixture's drain connects to another drain. In the case of wet venting, it has to be as the fixture's drain connects to the drain that is providing the wet vent.

So what you can't do is join the WC drain to the tub drain, and then join that to dry-vented lav drain, and expect the lav to wet vent both the WC drain and the tub drain. The vents for the WC and tub would need to be at that joint, not downstream where the lav comes in.

But if you joint the dry-vented lav fixture drain (= only one fixture) to the tub fixture drain (within the trap arm limits), and have the lav wet vent the tub. Then that branch (= more than one fixture) can join the WC fixture drain and wet vent the WC. And for the IPC, that order (tub first, then WC) is not required the lav could hit the WC first, then the tub.

Cheers, Wayne
So where the lav joins the tub, two 1.5” lines would need to be upsized to 2”, and the 2” vent off that line vents the wc,lav,and tub?
 

wwhitney

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Negative. Every trap gets vented at an elevation no more than one pipe diameter below the trap outlet (except a WC, which has external trap). So the lav trap needs to be vented above the floor, in all cases, and usually it is dry vented.

Then that dry-vented lav drain can join the tub drain (before or after joining the WC drain) and wet vent the tub drain. Again the tub trap arm can fall at most one pipe diameter between the tub trap and the wye were the lav wet vents it.

No need for any vent takeoffs below the floor, just the lav vent takeoff above the floor.

Wayne
 

Tudorrenovator

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I'd say oversimplified. : - )

The fixture's vent connection, whether wet or dry, needs to be (with one exception in the IPC) before or as the fixture's drain connects to another drain. In the case of wet venting, it has to be as the fixture's drain connects to the drain that is providing the wet vent.

So what you can't do is join the WC drain to the tub drain, and then join that to dry-vented lav drain, and expect the lav to wet vent both the WC drain and the tub drain. The vents for the WC and tub would need to be at that joint, not downstream where the lav comes in.

But if you joint the dry-vented lav fixture drain (= only one fixture) to the tub fixture drain (within the trap arm limits), and have the lav wet vent the tub. Then that branch (= more than one fixture) can join the WC fixture drain and wet vent the WC. And for the IPC, that order (tub first, then WC) is not required the lav could hit the WC first, then the tub.

Cheers, Wayne

In the photo below, for the lower level half bath near red number 3, could I add a vent after the wc and sink but before the mains stack, or the vent need to go where the sink joins, or before that?
 

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wwhitney

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In the photo below, for the lower level half bath near red number 3, could I add a vent after the wc and sink but before the mains stack, or the vent need to go where the sink joins, or before that?
Well, what do you think? How would the lav be vented, in accordance with my previous post?

Cheers, Wayne
 

Tudorrenovator

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Negative. Every trap gets vented at an elevation no more than one pipe diameter below the trap outlet (except a WC, which has external trap). So the lav trap needs to be vented above the floor, in all cases, and usually it is dry vented.

Then that dry-vented lav drain can join the tub drain (before or after joining the WC drain) and wet vent the tub drain. Again the tub trap arm can fall at most one pipe diameter between the tub trap and the wye were the lav wet vents it.

No need for any vent takeoffs below the floor, just the lav vent takeoff above the floor.

Wayne
So that dry vented lav is using a 1.5” pipe? And that size is enough to vent the WC, the lav and the tub?
 
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