Help a desperate DIYer...?

[ChuckGM]

I apologize in advance. I know we DIYer's can drive you guys nuts sometimes. But, here I am.... - Building a basement apartment. My diagram is the basics of the drain plumbing in the floor. The 4" drain to the left hooks into the main sewer line of the house about 6' left of this new toilet. Everything else depicted is 2" PVC. The two yellow spots are 2" vents. They tie together and then make their way to tie into the vent system. When I planned this (last year) it seemed to me that it is essentially a legal wet-vent set up (?) and that the two 2" vents were/are superfluous. Is that correct? Now though, I'm wanting to add a laundry drain off the end there by the sink. Can I do that without adding a vent? If it has to be vented separately, how big does it need to be and should I tie it into the sink as well or just leave that the way it is? Thanks very much for any answers/advice you can provide.

 

[Tuttles Revenge]

Since each fixture has its own individual vents your layout looks good. The laundry can use the same drain as the sink provided they're sized properly which 2" is in UPC. Some codes/juridicitons require 3" where a clothes washer hookup connects with other fixtures downstream.

If you wanted to make that a Horizontal wet vent then only the bathroom fixtures can be tied into it and laundry/kitchen get tied in downstream of the system. That could simplify a lot of extra venting.

 

[Sponsor]

 

[wwhitney]

How did you do (or plan to do) the vent takeoff on the shower trap arm? For a dry, the vent path needs to come off the top half of the pipe and rise at an angle of at least 45 degrees above horizontal, until 6" above the fixture flood rim.

Cheers, Wayne

 

[ChuckGM]

Since each fixture has its own individual vents your layout looks good. The laundry can use the same drain as the sink provided they're sized properly which 2" is in UPC. Some codes/juridicitons require 3" where a clothes washer hookup connects with other fixtures downstream.

If you wanted to make that a Horizontal wet vent then only the bathroom fixtures can be tied into it and laundry/kitchen get tied in downstream of the system. That could simplify a lot of extra venting.

Ok - so, if I'm understanding correctly, it all would have been fine as a horizontal wet vent if I'd stopped with the bathroom sink - (?) but the addition of laundry (and you are correct - kitchen sink - behind bathroom sink) to the same drain system requires that each fixture be vented individually? ----- The drains and the two vents already exist as depicted so tying in downstream with laundry/kitchen is not an option. The laundry/kitchen sink/bathroom sink are all within about 3 feet of each other. Can they share a vent?

 

[ChuckGM]

How did you do (or plan to do) the vent takeoff on the shower trap arm? For a dry, the vent path needs to come off the top half of the pipe and rise at an angle of at least 45 degrees above horizontal, until 6" above the fixture flood rim.

Cheers, Wayne

I'm fairly certain I did that correctly. it's under a lot of cement now tho so I'm not going to look. ;-)

 

[wwhitney]

Can they share a vent?

Every trap (and every WC) needs a vent. That can be a dry vent that comes off the fixture drain before it combines with any other fixture drains. Or in limited cases, it can be a wet vent, which is where the fixture drain connects with a branch drain that is carrying certain limited fixtures, one of which has a dry vent. The set of limited fixtures allowed in a horizontal wet vent is called a bathroom group and is basically just the fixtures you might find in a bathroom.

So, if the upstream most fixtures are a laundry and/or kitchen, that branch can not have any horizontal wet venting on it. Each fixture on the branch will need a separate dry vent. Any two dry vents can combine at a height of at least 6" above the flood rim of any fixtures being vented, so in that case they can be shared. But they can't be shared in the sense of a single dry vent takeoff serving two fixtures.

In other words, your kitchen sink and your laundry will each need their own dry vent takeoff, and you need to maintain the 3 yellow vents in your drawing. As an example of how you could use horizontal wet venting, if your dry vented kitchen drain and your dry vented laundry drain joined the 2" line that already carries both the shower and the lav (downstream of the wye where those two bathroom fixtures join), then your lav dry vent could wet vent your shower trap, and you could eliminate the dedicated shower dry vent. But with the kitchen/laundry drains coming in where you show them, you can't do that.

Cheers, Wayne

 

[ChuckGM]

Every trap (and every WC) needs a vent. That can be a dry vent that comes off the fixture drain before it combines with any other fixture drains. Or in limited cases, it can be a wet vent, which is where the fixture drain connects with a branch drain that is carrying certain limited fixtures, one of which has a dry vent. The set of limited fixtures allowed in a horizontal wet vent is called a bathroom group and is basically just the fixtures you might find in a bathroom.

So, if the upstream most fixtures are a laundry and/or kitchen, that branch can not have any horizontal wet venting on it. Each fixture on the branch will need a separate dry vent. Any two dry vents can combine at a height of at least 6" above the flood rim of any fixtures being vented, so in that case they can be shared. But they can't be shared in the sense of a single dry vent takeoff serving two fixtures.

In other words, your kitchen sink and your laundry will each need their own dry vent takeoff, and you need to maintain the 3 yellow vents in your drawing. As an example of how you could use horizontal wet venting, if your dry vented kitchen drain and your dry vented laundry drain joined the 2" line that already carries both the shower and the lav (downstream of the wye where those two bathroom fixtures join), then your lav dry vent could wet vent your shower trap, and you could eliminate the dedicated shower dry vent. But with the kitchen/laundry drains coming in where you show them, you can't do that.

Cheers, Wayne

I believe I have it... last question: So I tie into the vent system for the bathroom sink/kitchen sink/laundry - venting each into a shared "stack" above the flood rim that goes back to where the others vent.... What diameter does that new venting need to be?

 

[wwhitney]

Under the UPC, a 2" vent is required for a WC, and a 2" dry vent is good for up to 24 DFUs, when the total length to atmosphere does not exceed 120', of which at most 40' may be horizontal.

So basically everything on the lower level can be handled by one 2" vent. Here's the chart of DFUs:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#table_702.1

[That's California's version, up.codes says Minnesota uses the UPC but doesn't have their version, it's unlikely the table would be amended.]

There's also a UPC requirement that the aggregate vent area through the roof is no less than the smallest size building drain that could have been used. The latter is 3" for up to 3 WCs in the building, and 4" for 4 or more WCs, although some states have amended that threshold number of WCs. But if you have an existing DWV system for upstairs, it presumably should satisfy that requirement already.

Note that your basement dry vent has to rise up to the first floor but could possibly connect there with an existing 2" dry vent, at least 6" above the flood rim level of the fixtures it serves.

Cheers, Wayne

 

[ChuckGM]

Under the UPC, a 2" vent is required for a WC, and a 2" dry vent is good for up to 24 DFUs, when the total length to atmosphere does not exceed 120', of which at most 40' may be horizontal.

So basically everything on the lower level can be handled by one 2" vent. Here's the chart of DFUs:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#table_702.1

[That's California's version, up.codes says Minnesota uses the UPC but doesn't have their version, it's unlikely the table would be amended.]

There's also a UPC requirement that the aggregate vent area through the roof is no less than the smallest size building drain that could have been used. The latter is 3" for up to 3 WCs in the building, and 4" for 4 or more WCs, although some states have amended that threshold number of WCs. But if you have an existing DWV system for upstairs, it presumably should satisfy that requirement already.

Note that your basement dry vent has to rise up to the first floor but could possibly connect there with an existing 2" dry vent, at least 6" above the flood rim level of the fixtures it serves.

Cheers, Wayne

- sorry, follow-up.... So the existing vent that goes up stairs is 2" - If I add a run over to that 2" vent for the bath lav/laundry/kitch sink... does that new run also have to be 2"? - or could I use 1.5" for those 3 fixtures?

 

[wwhitney]

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#table_703.2

1-1/2" vent is good for 8 DFUs (but no WCs) and a maximum length of 60', of which 20' can be horizontal.

Cheers, Wayne