Horizontal Wet Vent Question

[Bill540]

I'm renovating a 1928 bathroom and I've got it stripped down to bare studs, joists, and rafters. The first image shows the studs, joists, subfloor, and the old DWV along with fixture locations (which I plan to keep):

In the second image fixtures and a couple of walls have been removed to get a better view of the old DWV layout:

The stack is cast iron (bluish), the other piping is galvanized. The galvanized for the waste upstream of the sink / tub joining wye is 1.5" (orange) and downstream it's 2" (red). It's an 8'x5' room and there is a bathroom on the third floor.

I plan to replace the galvanized with PVC but I was hoping to reuse much of the existing DWV routing through the joists but, unfortunately, the toilet trap has sections that are horizontal and dry and well below the flood line. I've seen web content suggesting a properly pitched dry horizontal vent below the flood line is OK, but, from what I can gather, there are good reasons why dry horizontal vents like this are not permitted by UPC code.

My local code (NYS) does permit horizontal wet venting, so, as shown in the third image, my idea is to have the line between the toilet 4x4x2 wye and the sink p trap serve as a wet vent for the toilet:

(same color conventions for PVC pipe width)

The old tub didn't drain particularly well and it was difficult to snake, so I took a direct route between the tub and the main stack. This approach will require more cuts to the joists and, assuming the new DWV layout is ok, my next step is to figure out what needs to be done to reinforce the joists.

Assuming proper slopes etc, does anyone see any glaring issues with the proposed DWV routing?

 

[John Gayewski]

I think your going to have a very hard time routing the tub drain through the joists like that.

 

[Sponsor]

 

[John Gayewski]

The drains are 2" after the 3x3 wye (with a 3x2 bushing) for the toilet. The trap arm's are 1.5" for the tub and 1.25" for the lav.

 

[GrumpyPlumber]

Ever seen really old home's bathrooms with their notoriously saggy floors?

Blame old school plumbers.

Hole diameter cannot exceed 1/3rd joist width and must have at least 2" inch of material above/below every hole.

Starting from the center height of the main in the corner, calculate a 1/4" pitch to the joist at the tub, add 1" inch to that center and see what you have left above it for that 2" of material.

If you have anything lass than 2x8 joists, you have a problem.

Notches cannot exceed 1/5th the joist width, I see a big problem right near the tub drain, if the diagram is accurate.... and tubs are heavy when full.

Wet vents have to be minimum 2".

In your diagram, the toilet is technically wet vented from the distance of the 2" drain to the vent stack, assuming the riser above the main is a vent, not a drain.

 

[Bill540]

The drains are 2" after the 3x3 wye (with a 3x2 bushing) for the toilet. The trap arm's are 1.5" for the tub and 1.25" for the lav.
View attachment 90023

> The drains are 2" after the 3x3 wye (with a 3x2 bushing) for the toilet.
The cast iron wye is 4x4x2, I'm assuming that won't change your advice.

Thanks, for your hints! So something like this?

 

[John Gayewski]

> The drains are 2" after the 3x3 wye (with a 3x2 bushing) for the toilet.
The cast iron wye is 4x4x2, I'm assuming that won't change your advice.

Thanks, for your hints! So something like this?

View attachment 90026

My vision includes you changing the cast iron piping to pvc. There's not much reason to keep any cast iron that can be removed in my opinion unless there's some other info not posted.

 

[Bill540]

Ever seen ...

> Ever seen really old home's bathrooms with their notoriously saggy floors?
My sag, as measured from the outside joist to the second joist is ~ 1.5 inches. The original tub was supported on one side by the studs and on the other side by the joists. The stud side stayed put and the other side dropped leading to one of the reasons the bathroom is getting rebuilt.

> I see a big problem right near the tub drain, if the diagram is accurate.... and tubs are heavy when full.
All the notches are existing and accurately depicted in the diagram. That's a 5 1/2" notch! It was (at some point) reinforced with some angle iron (not depicted).

> Notches cannot exceed 1/5th the joist width,
So notches can't exceed 7.5 / 5 = 1.5" ? I guess I'm in trouble if I want to route 2 3/8" OD PVC using notches.

> If you have anything less than 2x8 joists, you have a problem.
They are old dimensioned (1928) 2x8s.

> In your diagram, the toilet is technically wet vented from the distance of the 2" drain to the vent stack, assuming the riser above the main is a vent, not a drain.

Yeah, it's that dry, horizontal section of vent that I plan to get rid of.

> Hole diameter cannot exceed 1/3rd joist width and must have at least 2" inch of material above/below every hole. Starting from the center height of the main in the corner, calculate a 1/4" pitch to the joist at the tub, add 1" inch to that center and see what you have left above it for that 2" of material.

I need to research the topic, but maybe if I reinforce the joists w/ some plywood sisters I can take the direct route from the bathtub to stack.

 

[wwhitney]

I need to research the topic, but maybe if I reinforce the joists w/ some plywood sisters I can take the direct route from the bathtub to stack.

Plywood is not the best choice of material for that, as half the plies run the wrong way. Solid sawn lumber, LVL, or steel. Possibly two pieces, one top and one bottom.

Suggest you proceed by removing existing DWV within the joist bays, then jack and sister (with modern 2x8, kiln dried) any joists with a notch more that 1.25" deep or a hole bigger than 2.5" or closer than 2" to either edge. At that point you can drill 2-1/8" holes for 1.5" pipes and 2-1/2" holes for 2" pipes, staying 2" clear from the top and bottom of the joists.

Cheers, Wayne