Converting 1 bathroom to 2 full bathrooms

[Silver987]

Hi everyone. Looking for some help with a bathroom remodel we're in the planning stages for.

Background:
We're in NJ, so following NSPC 2021. We're DIY'ers getting some help from family with more experience but want to make sure we have a good solid plan before we apply for the permit.

The plan is to divide a large 2nd floor bathroom into two full baths. The current bathroom has a toilet, double sink, bathtub and separate shower. The joists run in direction indicated on drawing. We're basically going to divide the space with a wall and add a toilet and double sink (moving the existing toilet and bathtub).

The top drawing is the current layout. The bottom drawing is the proposed layout (changes are shown in orange). Drawing is not to scale; doors, windows, closets not shown (we already figured out clearances and have enough space). We also haven't started demo yet so are having a tough time figuring things out.

Some basic questions first:
1. For the new toilet on the left, can we move it as shown on the drawing on the bottom- approx 10 ft down, parallel to the joists? The NSPC seems to indicate it can be 10ft away if a 3" drain pipe is used with a 1/8" slope (is that right?). Does it matter what size the stack is? (I'm pretty sure mine is 3")

2. For the new toilet on the right, we're planning on going below the joists and making a soffit on the 1st floor to connect to the stack since we can't cut the joists that large. That would mean an approx 5ft run parallel to joists and then a 5ft run below the joists. Is that ok?

3. Any advice on how to create a riser diagram for the proposed drawing on the bottom? My uncle who's helping me says how to connect the pipes will be obvious to him once we demo but I have to submit the plan to the town for the permit ahead of time. I've been studying the NSPC 2021 and trying to see which of their diagrams match most closely to use as a guide but I'm just not sure and and I want to make sure my permit is approved and make sure this plan is possible before we demo anything.

4. Only the existing double sink on the left and the shower/tub on the right will be remaining in about the same location, everything else will be moving or being added. So if anyone has advice for the BEST way to plumb this I would love to hear it. We'll have most walls and the floor open so can remove existing plumbing and lay it out any way that works best. I'd rather take our time and do it right and not have trouble down the line, even if it is overkill for code.

Thanks so much for any help!!

 

[James Henry]

Nobody can do a thing for you until you uncover the existing plumbing pipes so they can tell you the best way to alter them. If you don't want to do that then you should hire a plumber to locate the drains and tell you what size they are.

 

[Sponsor]

 

[Jeff H Young]

I think you can get a pretty good idea of cource an exact layout is un known ill make a few suggestions .
answer to question 1 is its usually 3 inch but could be 4 . shouldnt matter though some codes were a max of 3 w/c on a 3 inch line so we dont know what you have.
q 2 yes good idea perfect should make this a piece of cake.
q3 i cant help you draw this
q4 since you are building a soffit id bring a new 2 inch line from the line in the soffit another piece of cake.
be a little easier to discuss if you numbered the bathrooms and put it on your plan.
bath 1 (left side ) id vertical wet vent the toilet with the tub and as mentioned the double lavs come from a new line in the new soffit
My gut feeling is the huge existing bathroom will have a joist on the left side the new toilet location is likely 3 to 6 inches to the left of existing toilet 12 inches off the wall instead of 15 to 18. if it was on a 16 inch layout im thinking a joist should be just about dead center of where the new toilet will be and would have been perfect for the original build in my area joist locations are often concidered and placed in a better spot on production homes or even custom homes if the plumber and carpenter get together. while you are at it figure out if the other toilet at bath 2 is going to work with existing joist layout. you might be able to determine existing joist layouts if it has vinyl flooring by driving nails in floor or with a stud finder in cieling below or even a hammer. I dont think your plans will matter as long as you follow code if structutral conditions require a diferant route you can pipe your house anyway you want so long as you meet code