Basement Bath Addition - UG Plumbing Plan

[djszp5]

Hello All,

I’m taking on a bathroom addition in my basement(will be bathroom #2 in the house) and am getting mixed feedback from the plumbers I’m talking to about size of underground piping. For my area we are subject to 2015 IPC/IRC/IBC.

• The existing concrete has been broken away to reveal a very shallow connection to the outgoing lateral (4” cast). At the completion of the underground plumbing my intent is to add 1” – 1.5” of leveler to the area to level and add meat to the slab.
• 3pc bath to be added (shower), along with a new laundry sink and re-establishment of an existing floor drain and washing machine drain.
• I have a new 2” vent line that installs from the basement joist space, through a wall cavity on the main floor, through attic and out the roof, with a single 45deg offset in the attic space
• I have spoken with three plumbers and all of them have said that my run to the proposed toilet will need to be in 4” because it’s underground. I have found some other threads on this site that indicate that 3” is acceptable, and I cannot find anything in the code that mandates 4” (or anything that differentiates sizing for above versus underground for that matter). Due to the shallowness of the connection to the lateral I am trying to reduce my pipe diameters and underground run lengths as much as allowable.
• Similarly, they are also saying that the modified floor drain must be a minimum 3” instead of the 2” that I have in my plans. Again, everything I see in 2015 IPC indicates to me that 2” is to code.
• What I can see for the DFU limitations per branch I feel that my attached design hits the mark, and I have a number of 2” vents that would route up above and connect to the new 2” to exterior that is installed.

At this time I’m really focused on how to address the bathroom and floor drain fixtures, as those are the ones going under the slab. I’m looking for a code callout that I can use to align with the AHJ on and introduce it to the plumbers that are telling me otherwise, primarily because I’m concerned that if I have to do 4” then I’m really going to be dealing with a thin bit of concrete poured back on top of the UG piping and possibly looking at having to raise the whole floor in this area, which brings new challenges around the minimum vertical clearance (Bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6’ 8”).

Does anyone see any issues with the layout I’m proposing or have any thoughts on the pipe sizing questions?

 

[wwhitney]

On the DFUs, a bathroom group (lav, bath/shower, and WC) is 5 DFUs, and a laundry group (sink and standpipe) is 3 DFUs. The floor drain is 0 DFUs. So I get 15 DFUs.

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Sizing of drains and sewers (drains outside the footprint of any building) is governed by IRC P3005.4. You can use 3" for the building drain and the building sewer, although using 4" for the building sewer would be more common. But as I understand it, you have an existing 4" cast iron building drain, and just want to connect one or more 3" branch drains to it, and won't be touching the building sewer at all. I see no problem with that.

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I'm unclear on your plans for routing the vents. Your drawing only seems to show fixtures 5-9, so I'll restrict my comments to those. You can use wet venting for the bathroom group, so a single 1-1/2" dry vent takeoff on the lavatory drain will suffice for the bathroom group. Typically the laundry sink and the washer standpipe would each have their own 1-1/2" vent takeoff; there are no wet venting allowances for laundry sinks or washer standpipes. So at an elevation 6" above all the fixture flood rims, you'd have 3 vent pipes rising into the ceiling, one each for the lav, washer standpipe, and laundry sink. They can combine with each other at any elevation above that, which would most likely mean in the ceiling framing above, but could happen within the walls.

The rule on dry vent location for a trap is that the the takeoff has to be within one trap diameter fall of the trap outlet. So if your trap arm falls at the minimum 1/4" per foot, that would mean with 6' of pipe run from a 1-1/2" trap, or 8' of pipe run from a 2" trap; run any steeper than 1/4" per foot, and they have to be closer.

Since you mention other fixtures not shown in the diagram, note that all venting needs to be done before drains from other fixtures join in. Mostly that means for wet venting the bathroom group, none of the other fixtures could join into the bathroom branch, they would all have to join downstream of the wye where the WC drain joins the combined shower/lav.

Cheers, Wayne

 

[Sponsor]

 

[John Gayewski]

Use 3"for the toilet and wet vented bathroom group. No comment on the drawing although it looks OK there are a few optimizations that could be made,and the vent should be at the lav. The cleanout I don't understand either.

For the toilet use a 4x3 closet 90.it makes it easier to connect the toilet later and that may be what the plumbers mean by it needing to be 4".

 

[djszp5]

Ok wow, thank you for the thoughtful feedback Wayne and John. I’m going to try to provide some further clarification and have included the same layout with some markups, as well as some photos of the current stack and intended tie in point.

@wwhitney Wayne

Sounds like I’m overestimating my DFUs a little bit and those come down based on groupings. Floor drain is 0, I like that. 0 DFU until there’s a break and it’s no longer 0 I guess?

Regarding the 3” vs 4” for the underground, hopefully the below picture gives you a sense of the lack of depth I’m working with. One of the plumbers mentioned it would be better to chip out a little more concrete in order to take out the cast combo wye that connects to the stack. If I’m going to bury it again either in concrete or in a wall, this makes total sense. So to come full circle to your response, this is a 4” drain leaving the home and I want to tie in to it with a 3” branch.

I’ve added green lines to show the possible vent routing.

I have a 2” vent run to the roof that is stubbed into the joist bay in the basement(held by riser clamp in the attic and U-clamp in basement). My joists are steel truss style, so for all of the vents needed I would go up into the joist interstitial space and bring them together to a common 2” before connecting to the stub.

Based on your comment, I would need a

• 1.5” vent off the lav that would serve as the dry vent for the lav and wet vent for shower and toilet
• 1.5” vent for laundry sink
• 1.5” vent for washer standpipe
• I’m also showing a vent for the floor sink, but would this not be required? I do not intend to route anything to it by design (and with that in mind, do I need to install a primer on it?)

Regarding the other fixtures in the house, the upstairs fixtures, see below picture of how they currently connect to the stack. I am really hoping that I can get the plumber to reroute these through the joists as much as possible to give me the most overhead clearance.

@John Gayewski,

Are you referring to the ‘CLEANOUT PORT’ I have upstream of the 2” wye where the floor drain trap leg connects in? I added this, possibly due to a misunderstanding of where I needed to have cleanouts related to how much direction change I have in the network. Happy to cut it if it isn’t required for any reason. I have a couple different 4”x3” closet bends on hand and know what you’re talking about, thank you.

Very much appreciate the feedback gentlemen.

Dave

 

[John Gayewski]

Ok wow, thank you for the thoughtful feedback Wayne and John. I’m going to try to provide some further clarification and have included the same layout with some markups, as well as some photos of the current stack and intended tie in point.

@wwhitney Wayne

Sounds like I’m overestimating my DFUs a little bit and those come down based on groupings. Floor drain is 0, I like that. 0 DFU until there’s a break and it’s no longer 0 I guess?

Regarding the 3” vs 4” for the underground, hopefully the below picture gives you a sense of the lack of depth I’m working with. One of the plumbers mentioned it would be better to chip out a little more concrete in order to take out the cast combo wye that connects to the stack. If I’m going to bury it again either in concrete or in a wall, this makes total sense. So to come full circle to your response, this is a 4” drain leaving the home and I want to tie in to it with a 3” branch.
View attachment 101596

I’ve added green lines to show the possible vent routing.

View attachment 101597

I have a 2” vent run to the roof that is stubbed into the joist bay in the basement(held by riser clamp in the attic and U-clamp in basement). My joists are steel truss style, so for all of the vents needed I would go up into the joist interstitial space and bring them together to a common 2” before connecting to the stub.

View attachment 101598
Based on your comment, I would need a

• 1.5” vent off the lav that would serve as the dry vent for the lav and wet vent for shower and toilet
• 1.5” vent for laundry sink
• 1.5” vent for washer standpipe
• I’m also showing a vent for the floor sink, but would this not be required? I do not intend to route anything to it by design (and with that in mind, do I need to install a primer on it?)

Regarding the other fixtures in the house, the upstairs fixtures, see below picture of how they currently connect to the stack. I am really hoping that I can get the plumber to reroute these through the joists as much as possible to give me the most overhead clearance.

View attachment 101599

View attachment 101600

@John Gayewski,

Are you referring to the ‘CLEANOUT PORT’ I have upstream of the 2” wye where the floor drain trap leg connects in? I added this, possibly due to a misunderstanding of where I needed to have cleanouts related to how much direction change I have in the network. Happy to cut it if it isn’t required for any reason. I have a couple different 4”x3” closet bends on hand and know what you’re talking about, thank you.

Very much appreciate the feedback gentlemen.

Dave

You have a 2"cleanout drawn. For what? It's a 4" (or 3") pipe. If anything needs cleaned I would say that long horizontal run of 2"for the shower and lav would be it. A wall cleanout there might actually get used.

 

[wwhitney]

I’m also showing a vent for the floor sink, but would this not be required? I do not intend to route anything to it by design (and with that in mind, do I need to install a primer on it?)

A dry vent for the floor drain is not required, you have it connected in a way that it can be wet vented by the lav/shower/WC drain. If one were required, it could not run horizontally under the slab in the way you have shown; it would come off the 2" floor drain fixture drain vertically as it passes under a wall, and stay vertical until at least 6" above the floor.

Your "emergency floor drain" will require trap seal protection per IPC 1002.4.1. A trap primer is one of those options listed there.

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I think John's point about the cleanout is that if it is provided in that location, then it should be a 3" cleanout. The 3" pipe should extend all the way from it to building drain. [And as previously commented, the 2" dry vent connection you have provided upstream of the cleanout is not useful.]

No comment on whether that cleanout is required or a good place for one, or whether other locations would be better. The IPC rules on cleanouts, which I'm not familiar with, are here:

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Cheers, Wayne

 

[foplumbing]

On the DFUs, a bathroom group (lav, bath/shower, and WC) is 5 DFUs, and a laundry group (sink and standpipe) is 3 DFUs. The floor drain is 0 DFUs. So I get 15 DFUs.

Chapter 30 Sanitary Drainage: Sanitary Drainage, Missouri Modular Residential Code 2015 | UpCodes

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Sizing of drains and sewers (drains outside the footprint of any building) is governed by IRC P3005.4. You can use 3" for the building drain and the building sewer, although using 4" for the building sewer would be more common. But as I understand it, you have an existing 4" cast iron building drain, and just want to connect one or more 3" branch drains to it, and won't be touching the building sewer at all. I see no problem with that.

Chapter 30 Sanitary Drainage: Sanitary Drainage, Missouri Modular Residential Code 2015 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

I'm unclear on your plans for routing the vents. Your drawing only seems to show fixtures 5-9, so I'll restrict my comments to those. You can use wet venting for the bathroom group, so a single 1-1/2" dry vent takeoff on the lavatory drain will suffice for the bathroom group. Typically the laundry sink and the washer standpipe would each have their own 1-1/2" vent takeoff; there are no wet venting allowances for laundry sinks or washer standpipes. So at an elevation 6" above all the fixture flood rims, you'd have 3 vent pipes rising into the ceiling, one each for the lav, washer standpipe, and laundry sink. They can combine with each other at any elevation above that, which would most likely mean in the ceiling framing above, but could happen within the walls.

The rule on dry vent location for a trap is that the the takeoff has to be within one trap diameter fall of the trap outlet. So if your trap arm falls at the minimum 1/4" per foot, that would mean with 6' of pipe run from a 1-1/2" trap, or 8' of pipe run from a 2" trap; run any steeper than 1/4" per foot, and they have to be closer.

Since you mention other fixtures not shown in the diagram, note that all venting needs to be done before drains from other fixtures join in. Mostly that means for wet venting the bathroom group, none of the other fixtures could join into the bathroom branch, they would all have to join downstream of the wye where the WC drain joins the combined shower/lav.

Cheers, Wayne

floor drains are 2 dfu. only emergency floor drains are 0

 

[djszp5]

I do not have anything running to my floor drain and will not post-remodel, it will only be used in the event of a line rupture, does that therefore constitute it as an emergency drain?

 

[wwhitney]

floor drains are 2 dfu. only emergency floor drains are 0

This is a point of difference between the IPC and the IRC. You are correct for the IPC, with some exceptions. Whereas in my post, I provided a link to IRC Table P3004.1, which lists DFUs for fixtures, and which says:

"Floor drain 0 DFU (footnote b)

(b) A floor drain itself does not add hydraulic load. Where used as a receptor, the fixture unit value of the fixture discharging into the receptor shall be applicable."

So if the project is a single family house in a state that has adopted both the IPC and the IRC plumbing P chapters, then you'd need to check the scope chapters of both the IPC and the IRC to see which one applies to the project. Usually it's the IRC, although sometimes you have the option to use the IPC instead.

Cheers, Wayne

 

[djszp5]

Thanks again Wayne, I will take this question back to the plan reviewer.

Going back to the slab thickness concern... I have the dimensions and slope calcs for all of the fixtures I’m looking to add, along with the minimum concrete thickness for each branch shown in red. Is there a minimum thickness per code that an inspector will hold me to here?