Ensuite addition, check my layout

[Armindilo]

Hello All. I've followed this forum off and on for a few years, and I find it to be an amazing resource. I've checked as many threads as I could reasonably find to try to get my layout correct before posting this here. But I am just an electrician, not a plumber, so please have a look at my layout and let me know if I've got this right! I've got two options drawn out for the shower and for the existing stack, since I'm not sure yet what exactly I'll be able to do with regards to locations of joists, slope, etc. I also added a top view plan of the space to help understand whats going on. There are a few things that might not be clear in the drawing, and a some things I have specific questions about; I'll list them below. I'm in NL, Canada.

1. I see the shower as a wet vent for the toilet, therefore 2" all the way back to the 3" vent stack. Did I get this right?
2. The lav and shower drains would enter the 3" horizontally (wye & 45). They may be turned up slightly, but less than 45°. Is this correct?
3. The vent for the shower will enter at 45° or higher. Correct? And does it need a wye, or is a santee ok here?
4. I've drawn two options for entering the existing 3" stack. I'd like to just use a santee (horizontal to vertical santee is ok, right?). I suspect there might be a tee already there for an existing toilet, so to keep everything inside the joist and walls, I could turn down and join in lower with a wye; Is this acceptable? And what type of 90° elbow is acceptable here; I'd like to keep it as small as possible.
5. The turn in the 3", and the bottom elbows of the shower and lav are sweep elbows. The rest are vent elbows.

Any and all comments welcome! I want to get this right and if there is anything that could be done better or easier, I'd love to know before I start putting it in! Thank in advance.

EDIT: Uploaded better images.

 

[wwhitney]

My comments are based on the primary US codes (IPC and UPC), your code in Canada will differ so you need to check what it says.

1) The shower can wet vent the WC. The UPC requires a 2" vent for a WC, so under it the shower dry vent would need to be 2". Under the IPC, it could be 1-1/2".

2) The lav need to be dry vented, so its drain is unrestricted as to how it joins the WC drain. If the shower is horizontally wet venting the WC, then the convention is to join it to the WC with a combo (wye plus 45) at 2% slope. I'm not aware of any reason you couldn't roll it up a bit higher, if it is already vented (i.e. see #6 below).

3) The shower dry vent needs to be taken off vertically, meaning that the vent is at most 45 degrees off plumb. And it needs to stay vertical until 6" above the shower flood rim, i.e. it may not go horizontal below the floor. I think one of your two isometrics violates this requirement.

As for the fitting used, the UPC requires a wye or combo, while the IPC would allow a san-tee on its back. The only upside to the latter is if space is tight, so even if your code allows the san-tee on its back, I suggest a combo if it fits.

4) A santee is allowed for drainage with the straight path vertical (up to 45 off plumb) and the side entry horizontal. Either a san-tee or a wye is fine for the 3" branch drain to join your stack. For 90 degree drainage bends, you use a LT90, except that when drainage is turning from horizontal to vertical you may use a quarter bend. Which applies to your lefthand isometric.

5) Vent elbows are sharper than quarter bends, and are only allowed in vents. They are also a bit more expensive than quarter bends in my experience, so the only upside is if space is really right on a vent. In other words, there's no point to using vent 90s unless spatially necessary.

6) As far as an easier option, under the IPC you could eliminate the shower dry vent and arrange for the lav to wet vent the WC and the shower. To do that you'd just need to join the shower to the WC drain after the lav drain. So either send the shower drain farther to the right, or move the lav stack to the left. [The lav stack doesn't have to be behind the sink, you can have a horizontal lav trap arm in the wall behind the side.] You just have to be sure that the lav and shower trap arms are within the maximum allowed length and have no more than one pipe diameter of fall.

Under the UPC, this would be harder to do, as it requires the WC to be the last fixture on the wet vent. I.e. the connectivity would have to be lav joins shower, then the combined drain joins the WC (and the lav drain and vent would have to be 2" as previously mentioned.) I think you'd have to push the lav stack all the way to the left of the WC, so its drain can come around the WC closet flange and hit the shower first.

Cheers, Wayne

 

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[Armindilo]

Wayne, Thank you for all your comments. They are really helpful.

As it turns out, what I thought was the existing stack for the toilet is actually just for the shower; the existing toilet takes a different path. This means we would have to incorporate a few too many bends and box out the ceiling, which we don't want to do. So our plan now is to run the other direction, to the outside wall and run a 3" down to the basement floor and tie into the drain in the concrete.

I was going to attach another couple ideas for a layout, but I'm running into issues, so I'll need to think about it some more. Specifically the problem I'm running into is that I'm trying to stay within the height of joist cavity (2x10). I wanted to put the shower vent in the wall behind the shower, but then I'd have to run two 2" pipes on top of each other, which wouldn't leave me room for the proper slope without drilling holes too close to the edgs of the joists. I could almost wet the shower from the lav, but the trap arm would be just over 60", which I understand is the maximum. Back to the drawing board...