New Plumbing DIY layout

[RMCB]

Hello all,
I've recently moved my mother into a studio space above our garage, but it's in a mostly unfinished state. Our biggest priority is getting drainage setup since her septic tank is finally going in the ground, so she can actually have a toilet. I'm doing the work myself to save money, but my plumbing experience is pretty limited. At this point, I've read through some of the IPC code, and watched a ton of youtube videos. I found this tool online to illustrate what I'm going for and laid out the critical components, minus the venting.

In the attached image, and the link you can follow to view in 3D HERE, I've laid out the main fixtures from left to right, a 30x60 tub (I was unsure how to model this in CraftyAmigo, so it's just a P trap), a toilet, single sink lav, washing machine, then kitchen sink and dishwasher, that then runs downstairs to a 4" pipe that will be connected to the septic. The exterior walls are represented in solid panels, and the interior walls are represented by the blue colored framing. The actual framing looks much better in reality than my hacked together 3D plan. All the dimensions are inaccurate but the total run of the back wall is around 28 ft.


I guess the venting is my biggest question. Previously I had laid out the venting to be a 2" wet vent that came up from the tub drain, with the addition of a 3" vent through the roof per code for our cold climate. Initially I had planned to run the vent from the corner to the left of the toilet where I currently have a cleanout, but I figured it'd be easier to go through the roof closer to the interior wall at the tub P trap since I'll have more clearance in the attic to work, as opposed to near the eave. I wanted to wet vent based on a video I watched by Rising Tide Plumbing on youtube, and to save money on the extra materials, but after sending it to a plumber through the website JustAnswer, I got a pretty rude shutdown and little actual information.


Anyway the long and short of it is, I want to run as little venting as needed through the interior wall if possible. Would my wet vent from the tub area be enough to cover the rest of the drainage? Or should I just run a 3" vent from the corner by the toilet? Hopefully this makes sense. Thanks for your time!

(Edit: This is my second time posting this. I read somewhere the URL links may be sabotaging my post so I will attach them following this initial post.)

 

[RMCB]

The links for the design in 3D here: CraftyAmigo Design
as well as the video I reference: Rising Tide Plumbing Video

 

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[RMCB]

Ok so after some further research, I think I've come pretty close to a final design.

3D viewable here

I've made the vent pipes blue for clarity. The far exterior wall is also the eave of the roof, so ideally I want my venting in the interior wall so I'll have head space to work in the attic. Vents for the washer and kitchen sink tie into the main stack in the attic. The kitchen sink drain is a little odd due to the window directly above and I want to hide the drain in the cabinet space. I'm not entirely sure the wye I've added for the wet vent downstream of the tub drain would be approved, or if there is a better start point for the bathroom group venting? I've started to make my openings in the subfloor and of course both of my drains so far have been directly over a joist, so I've spent the last couple days making plumbers boxes for the tub and toilet, but I'm nearing the point of getting pipe actually put together, so any advice is greatly appreciated! Thanks again.

 

[Reach4]

Tub trap needs a vent. Lavatory (bathroom sink) needs a vent.
Kitchen sink needs a trap.

 

[RMCB]

Not sure why the image came out so small so it may be hard to see without viewing the 3D plans, but there is already a trap for the sink. Lav and rest of the bathroom group is wet vented off the wye on the left.

 

[Reach4]

Not sure why the image came out so small so it may be hard to see without viewing the 3D plans, but there is already a trap for the sink. Lav and rest of the bathroom group is wet vented off the wye on the left.

I see your lav trap on the 3-D.

The lav will need to be dry-vented, but it could wet vent the shower and toilet. You would need to run a 2-inch drain(wet vent) from the lav, over to the left, perhaps in the wall, and feed that into the path within 8 running feet (IPC) of the output of the shower trap. A wet vent can go horizontal under the floor.

Your vent for the shower is no good under IPC, because the dry vent runs horizontally under the floor. Instead you would run the trap arm over to the wall, where you dry vent that, and then turn off to the toilet. In that case, add another dry vent with VTR (vent thru roof) or AAV for the lav-only.

Will your cleanout to the left of the toilet be accessible?

 

[Reach4]

Iooked at your 3d some more... more problems.

Right hand trap needs to be vented before turning down. One way is to stay horizontal all of the way to the vent sanitary tee.

Venting to your vertical vents need to be sanitary tees. Your graphics look like combos. Maybe you just picked the wrong images, and meant santees.

 

[RMCB]

So I'm trying to avoid running pipe in the exterior walls (represented by solid panels in the 3D) due to our cold climate. My only interior wall space will be the two walls shown with the framing towards the front view. Why would the lav need it's own venting? Is it too far from the main dry vent? Or does it have something to do with the horizontal turns? I've seen lots of designs where the lav is the main origin of the wet vent, and very few where the wet vent starts with the tub area, but unfortunately, that's not going to work well for me considering I only have a few inches of head space in the attic above the lav and I would have to run the pipe in an exterior wall and risk freezing. My understanding is that IPC allows a 2" wet vent for an entire bathroom group, which is why I've designed it the way it was.

So based on your advice I changed the design to fix the right hand trap, the vent santees, and the tub vent area. I also added an extra cleanout beneath the vent stack. The other cleanout would have been accessible, but now it is even more so.

Here is the updated link for the 3D image

 

[Reach4]

So I'm trying to avoid running pipe in the exterior walls (represented by solid panels in the 3D) due to our cold climate. My only interior wall space will be the two walls shown with the framing towards the front view. Why would the lav need it's own venting? Is it too far from the main dry vent? Or does it have something to do with the horizontal turns?

Dry vents cannot run horizontally unless 6 inches higher than the flood level.... The dry venting has to take place before the drainage turns down more than the diameter of the trap arm.

Is that slab under the floor, or crawlspace or basement? With slab, your drain could run at an angle, but you mention joists.

If slab, how do you get to your cleanouts?

So here is a rough idea of using a single VTR for the bath group. Line L-J must be 6 ft max if 1.5 inch trap and pipe, and 8 ft if 2-inch trap and pipe.

There is some disagreement as to whether you can bring in the toilet to get wet vented from above. If you bring the toilet waste in from the side, everybody will like that. H-C is in the wall or fits behind the toilet next to the wall, perhaps in a floor soffet (I don't know the correct term for a box where baseboard would go), but you could bring that below the floor instead. I have another picture with an alternate idea.

 

[RMCB]

All the fixtures are going to be on a 2nd floor studio space, so underneath is a garage with ~10' ceilings. They will eventually tie into a 4" pipe exiting the structure and going into a new septic being installed.

Dry vents cannot run horizontally unless 6 inches higher than the flood level.... The dry venting has to take place before the drainage turns down more than the diameter of the trap arm.

Ok, so I understand that is why my previous design wouldn't be to code due to the horizontal dry vent in between the tub and toilet fixtures.

The lav will need to be dry-vented, but it could wet vent the shower and toilet. You would need to run a 2-inch drain(wet vent) from the lav, over to the left, perhaps in the wall, and feed that into the path within 8 running feet (IPC) of the output of the shower trap. A wet vent can go horizontal under the floor.

You mentioned previously the lav (p-trap to the right of the toilet) would need it's own vent, but wouldn't it be considered part of the bathroom group and eligible as part of the horizontal wet vent? If not, I imagine I would be able to connect it opposite the kitchen sink in the same manner using a double santee like the image below.

 

[Reach4]

Alternate.... vent lav with https://rectorseal.com/magic-trap-kit/
Dry vent tub, which wet vents toilet.

 

[Reach4]

You mentioned previously the lav (p-trap to the right of the toilet) would need it's own vent, but wouldn't it be considered part of the bathroom group and eligible as part of the horizontal wet vent? If not, I imagine I would be able to connect it opposite the kitchen sink in the same manner using a double santee like the image below.

I think that would also work to vent the lav. Turquoise 4-port fitting is a double fixture fitting. I think you want the kitchen waste expanded to 2 inch beyond the trap adapter. Also, kitchen waste is higher probability of clogs, so a cleanout would be good.

Tub cannot wet vent something higher. Lavs are high, so they need to be dry vented, but they can wet vent other bath stuff. It is possible for a lav to wet vent a lav.

See the bottom of page 12 of https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf for big IPC wet vent diagram.

 

[RMCB]

Tub cannot wet vent something higher. Lavs are high, so they need to be dry vented, but they can wet vent other stuff.

Ahhh that's the missing piece of the puzzle. Thank you for explaining that. That explains why all the technical drawings I've seen always use the lavs for the vent since they are the highest point.

In that case, I think I'll plan on doing the double santee since most of the rightmost side of the bathroom area is going to be cabinets that I can hide the pipe in, similar to the kitchen sink on the opposite side.

So my new layout for the tub drain area seems to be near identical to your second image (img_7), and then I changed both the sink and lav to run horizontally until they reach the vent. So unless I'm forgetting something, would it be safe to assume this design would get a pass?

 

[Reach4]

I think I'll plan on doing the double santee

While there exists a double santee, you want the one called the double fixture fitting.

See place P.... how to implement a vent and a turn takes some thought. One way is to run the vent into a santee on its back, and continue to a long sweep to make the turn.

Charlotte PVC 311 is
Long Sweep 1/4 Bend,
with Side Inlet
ALL HUB

3X3X2(PVC)
However you would be looking for 2x2x2. So the 2x2x2 santee followed by a long sweep uses available parts.

A santee on its back would be positioned such that a bug running down the vent would be directed away from the tub trap. You could also use a combo, which would be usable for UPC as well as IPC.