Venting Bathroom

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Duffman56

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I'm planning to do the plumbing for my master bathroom addition. I have run some PEX and some PVC for the main supply to the house, but never drain lines.

I'm hoping to get enough questions answered today that I can buy the majority of the materials I will need at Home Depot when I'm in "the city" this afternoon. I'm attaching a rough drawing that hopefully gives an idea of what I'm trying to do.

I'm planning on a 2" vent stack running to the roof, in the wall behind the toilet. I plan to tee together the sink vents in the wall and run a single 1-1/2" vent stack vertically up from the sinks, into the 2x6 ceiling joist space, where a lateral run will tie this vent into the 2" vent stack behind the toilet. Will this work, or should I be using two separate 1-1/2" lines that tie into a 2" since there are two sinks?

I'm not sure how to vent the corner tub and toilet. Would a separate 2" vent stack in the 2x4 wall be the easiest solution here?
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wwhitney

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Any elbow carrying drainage whose outlet is horizontal needs to be a long sweep. I.e. the 3" elbow at the top right you ask about.

Dry vents have to take off vertically (at least 45 degrees above level ) and stay vertical until at least 6" above the fixture flood rim. So you can't dry vent the WC like that in the wall behind it, you'd have a horizontal dry vent below the floor. [Well, if the horizontal drains were, say, 18" below the floor, then you could rise at a 45 back towards the wall and get under the wall before you rise above the floor.]

However, if you upsize the drain that is carrying both lavs to 2", then that drain can wet vent the WC, and you can just delete that WC dry vent. A section of drain that is carrying only one lav can be 1-1/2" and still be a wet vent, but for 2 lavs it has to be 2". You can upsize the vent for the lavs to 2" if you want, but the IPC does not require that.

As to the shower/tub, the way you have shown it is fine. The shower is dry vented, and it wet vents the shower. Note that each trap arm (from trap outlet to vent connection, either the dry vent takeoff for the shower or the wet vent connection to the shower drain for the tub) has to be horizontal and fall no more than one pipe diameter, but at least 1/4" per foot.

Or if you wanted to avoid the dry vent in the wall between the shower and tub, the double lavs can wet vent both the shower and tub as well. To do that you'd need to join the shower drain and the tub drain to the 3" line separately, rather than combine them before they join the 3" line. And the connection to the 3" line would be the wet vent for each trap, so the resulting longer trap arms would each need to meet the length and fall limits (8' run and 2" fall for a 2" trap).

Some (many?) consider a dry vent to be better than a wet vent, so that would be argument for keeping the dry vent between the tub and shower.

Cheers, Wayne
 

Duffman56

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Any elbow carrying drainage whose outlet is horizontal needs to be a long sweep. I.e. the 3" elbow at the top right you ask about.

Dry vents have to take off vertically (at least 45 degrees above level ) and stay vertical until at least 6" above the fixture flood rim. So you can't dry vent the WC like that in the wall behind it, you'd have a horizontal dry vent below the floor. [Well, if the horizontal drains were, say, 18" below the floor, then you could rise at a 45 back towards the wall and get under the wall before you rise above the floor.]

However, if you upsize the drain that is carrying both lavs to 2", then that drain can wet vent the WC, and you can just delete that WC dry vent. A section of drain that is carrying only one lav can be 1-1/2" and still be a wet vent, but for 2 lavs it has to be 2". You can upsize the vent for the lavs to 2" if you want, but the IPC does not require that.

As to the shower/tub, the way you have shown it is fine. The shower is dry vented, and it wet vents the shower. Note that each trap arm (from trap outlet to vent connection, either the dry vent takeoff for the shower or the wet vent connection to the shower drain for the tub) has to be horizontal and fall no more than one pipe diameter, but at least 1/4" per foot.

Or if you wanted to avoid the dry vent in the wall between the shower and tub, the double lavs can wet vent both the shower and tub as well. To do that you'd need to join the shower drain and the tub drain to the 3" line separately, rather than combine them before they join the 3" line. And the connection to the 3" line would be the wet vent for each trap, so the resulting longer trap arms would each need to meet the length and fall limits (8' run and 2" fall for a 2" trap).

Some (many?) consider a dry vent to be better than a wet vent, so that would be argument for keeping the dry vent between the tub and shower.

Cheers, Wayne
Not sure I fully understand you about the dry vents, but if I do, I was planning on running the 1-1/2" dry vents up in the wall cavity, then going lateral once they were above the ceiling line. Then into the 2" dry vent behind the toilet. Everything would be vertical until it got about 6' above the sinks. Either way, sounds like running 2" drain lines to the sinks would be MUCH easier, since it means no dry venting at all for the sinks. That being said, do I need the 2" dry vent behind the toilet or can a toilet wet vent as well? Seems like a lot of water going down at once but I thought I read some places do not require dry venting on toilets.

I may go ahead with the vent stack between tub and shower, since it will allow for one single run of pipe into the 3".

Thanks for your detailed explanation! It's very much appreciated!
 

wwhitney

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Not sure I fully understand you about the dry vents, but if I do, I was planning on running the 1-1/2" dry vents up in the wall cavity, then going lateral once they were above the ceiling line. Then into the 2" dry vent behind the toilet. Everything would be vertical until it got about 6' above the sinks. Either way, sounds like running 2" drain lines to the sinks would be MUCH easier, since it means no dry venting at all for the sinks. That being said, do I need the 2" dry vent behind the toilet or can a toilet wet vent as well? Seems like a lot of water going down at once but I thought I read some places do not require dry venting on toilets.
I think you got that a bit backwards. The dry vent at the lavs is absolutely required.

The issue is the dry vent you show at the WC, pretend the lavs aren't there for the moment. You have a closet flange 12" off the back wall, yet you show a dry vent for the WC on the back wall. Consider the piping arrangement that would require, and look at what part of that piping carries drainage. All the rest of it is dry vent. Doesn't that dry vent include a horizontal portion below the floor for the 12" between the WC closet flange and the back wall? That horizontal dry vent below the floor isn't allowed.

So I was saying you could increase the lav drain size, keep the dry vent at the lavs, and delete the dry vent at the WC.

Cheers, Wayne
 

Duffman56

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Oh shoot, I did read it backwards. What if I keep the dry vent location (for attic reasons), but have it 90 in the ceiling, towards the sinks' dry vents? Then I have the sink drains tie into the 3" line. Would this work? If so would I need to use 2" for dry vent and wet vents for sinks? Hopefully that wouldn't be taking too much wood out of the 2x4 walls and sill plates?
 

wwhitney

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Plumbing-wise, in the wall behind the WC/lavs, you can do whatever you want with the lav dry vent once it's 6" above the lav flood rim. The minimum sizes are 1-1/2" for the lavs dry vent, 1-1/2" for a wet vent that is carrying only one lav, and 2" for a wet vent that is carrying two lavs.

If the wall behind the lavs is not load bearing, then you can drill the wall studs at 60% of their width, or up to 2.1". That's enough for a 1-1/2" Schedule 40 pipe, which is 1.9" OD.

Cheers, Wayne
 

Duffman56

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Well, I'm definitely showing my lack of plumbing experience here, but I do greatly appreciate your help.

From your last post it sounds like I have two options.

1) I can use 1-1/2" dry vents for the lavs and vent them through the roof. Does the dry vent need upgraded to 2" at any point, or is it good at 1-1/2" throughout? Am I ok with 1-1/2" drain lines off each lav? Would I need to convert to 2" once it's carrying drain water from both lavs? Would I need a separate WC vent with this setup or is it venting through the lavs vent?

2) I can use 2" drain lines off each lav, which will act as wet vents. Sounds like I'd be taking a bit too much out of the bottom sill plate than I should. Same question as above - would I need a separate WC vent for this, or is it venting through the lavs?

Thanks Wayne!
 

wwhitney

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2) No, the lav drain can never act as a wet vent for the lav itself. The lav itself needs a dry vent. Then the dry vented lav drain can act as a wet vent for other fixtures, like the WC.

1) No, good at 1-1/2" / Yes / Only if you want it to wet vent the WC / Either a separate dry vent for the WC, or use the lav drain to wet vent the WC.

Cheers, Wayne
 

Duffman56

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1) No, good at 1-1/2" / Yes / Only if you want it to wet vent the WC / Either a separate dry vent for the WC, or use the lav drain to wet vent the WC.

Cheers, Wayne
OK. I think I finally have it down. I'll plan on only the lavs having a dry vent. I'll run 1-1/2" dry vents from the lavs all the way through the roof. Then I'll run 1-1/2" drain vents from each sink, that convert to 2" once the drain is handling both sinks. This 2" line will tie in to the 3" line, maybe through a 3" elbow with 2" side inlet.

Given what was said about the hole size in 2x4 framing, would I be ok with just one 1-1/2" dry vent for the tub and shower?
 

wwhitney

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OK. I think I finally have it down. I'll plan on only the lavs having a dry vent. I'll run 1-1/2" dry vents from the lavs all the way through the roof.
Those two 1-1/2" lav vents can combine into a single 1-1/2" vent through the wall top plate, as long as the combination and horizontal vent sections are at least 6" above the lav flood rims.

This 2" line will tie in to the 3" line, maybe through a 3" elbow with 2" side inlet.
Not with that fitting. Use a regular closet bend (quarter bend, which is the one exception to the first sentence of my first post), and downstream of that, use a wye or combo in a horizontal orientation (both inlets at 2% slope) to connect the horizontal lav drain/wet vent to the horizontal WC drain.

Given what was said about the hole size in 2x4 framing, would I be ok with just one 1-1/2" dry vent for the tub and shower?
In your original drawing, with the shower dry vented, and then the shower drain wet venting the tub, the dry vent taken off the shower only needs to be 1-1/2". In the ceiling framing that 1-1/2" dry vent could combine with your lavs 1-1/2" dry vent to be a single 1-1/2" dry vent (or 2" if you prefer).

Cheers, Wayne
 

Duffman56

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So I need to bring the 2" line into the 3" line after the elbow. I think my drawing matches what you're saying.

I may run the two 1-1/2" dry vent stacks, or may combine them all into one in the ceiling. I'd have to drill through a lot of 2x6's to combine, and I was thinking 1-1/2" wasn't enough vent for 11-12 DFU's, but I'll take your experience over mine any day. Thanks!
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wwhitney

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So I need to bring the 2" line into the 3" line after the elbow. I think my drawing matches what you're saying.
Yes, that drawing matches if the lav drains overlaying the wall represent drains in the floor framing, with the wall framing having a 1-1/2" san-tee behind each lav trap, with a 1-1/2" vent out the top and a 1-1/2" drain dropping down into the floor framing. Where the two lav drains combine in the floor framing you'd need a 2 x 1-1/2 x 1-1/2 combo (which could be a combo with 1 or 2 2" inlets that have 2x1-1/2" bushings in them).

I may run the two 1-1/2" dry vent stacks, or may combine them all into one in the ceiling. I'd have to drill through a lot of 2x6's to combine, and I was thinking 1-1/2" wasn't enough vent for 11-12 DFU's, but I'll take your experience over mine any day. T
So, I don't have any direct experience with IPC plumbing, here the code is the UPC. But for branch vents my understanding is that the minimum IPC vent size is half the drain size. If you want to dig into it more, the details are here:


Cheers, Wayne
 

Duffman56

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Wayne - you have been a huge help. Many many thanks. If you’re ever out in western KS the drinks are on me.
 
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