Small Cabin Rough In for DWV - Am I On The Right Track?

[Jedrek4680]

Since July I've been self-building a 500sqft cabin which has been a perfect way to keep busy and away from others. It has been an incredible learning experience and so rewarding to work with my hands (I am stuck on a computer all day for my day job so this is a welcome change). I got things weathered in before snow, and am now working on adding the utilities over the winter months. I really enjoy learning and doing these things myself, but am outsourcing the electrical and propane hookups for insurance reasons.

The plumbing I would like to do myself and have been reading up on what I need and pieced together knowledge from the National Plumbing Code of Canada, various books, websites, and this forum which have all helped me get a basic understanding of how to rough in my drain, waste, and vent piping.

I'm hoping to get some feedback on the design I came up with and understand 2 main things:
1) Is there anything here that is WRONG?
2) Is there anything I can do to make this more efficient without sacrificing function?

The cabin is on a pier and beam foundation and I have pretty good access underneath. The kitchen and bathroom are back to back so all the plumbing is concentrated within a small area. There's a loft above and I'm trying to avoid putting plumbing in the exterior walls where possible. We're also pretty remote so we'll be using solar on the south roof so I am trying to keep the stack vent in the corner so it's out of the way as much as possible.

Pic 1 is the floor plan to show where the fixtures and non-load-bearing 2x4 wall is located

The small closet beside the stacked washer/dryer will serve as a utility closet housing the HRV/ERV, tankless propane hot water heater, well control box, pressure tank, and hopefully have a little bit of room left for some storage.

Pic 2 is a SketchUp drawing of the DWV rough in that I came up with. I am not the best with this software so I can't figure out how to change the piping sizes without starting from scratch but the toilet arm and waste pipe below the floor would all be 3" as well as the main stack vent up thru the roof.

I put the vents up thru the loft floor joists since I am able to bore holes of sufficient diameter in those 2x12s for the horizontal connections, but not in the 2x6 exterior wall studs. The kitchen piping I have kept just outside of the wall and the trap arm will end up behind base cabinets and the stack portion would be in the utility closet.

Pic 3 is another SketchUp view from below.

There is also a 4ply beam below the floor joists which prevents me from going straight down thru the sill. I couldn't figure out how to sketch this with a 45 degree bend so there are 2 90s instead. I was intending to do a 45 from below the sill to use less fittings and smooth things out.

So, am I on the right track here? Anything wrong? Anything I can improve?

Thanks in advance for any feedback!

 

[wwhitney]

I'm only familiar with the US codes, but expect the Canadian code to be similar. Looks like you are individually venting everything, as I see 5 vents rising to the loft floor system. The short vertical wet vent section you've drawn on the WC drain is probably not allowed, but there's no need for it, just switch the order of the two san-tees on the vertical stack.

The shower trap is not correctly vented, but it is easily fixed by lowering the trap to avoid the vertical jog just downstream. The horizontal fixture drain from the trap outlet to the vent take off is called the trap arm, and it needs to have a maximum fall of at most 1 pipe diameter. This rule prevents the trap arm from filling with water and siphoning the trap.

With the US horizontal wet venting rules, you could do the venting with just 3 vent take offs--one for the kitchen sink, one for the laundry, and one for the bathroom fixtures (WC, shower, lavatory). To do that you'd bring the WC drain and the shower drain into the horizontal lav drain before any other drains (kitchen sink or laundry) join in. One of the two main US codes would require the WC to be after the shower; the other doesn't care.

Cheers, Wayne

 

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[Jedrek4680]

Thanks for the suggestions Wayne, very helpful and much appreciated!

I can easily switch the WC to run above the other main horizontal drain line and eliminate that short wet vented portion on the main stack.

Alternatively the National Plumbing Code of Canada does allow the WC to be wet vented as long as the WC is the last fixture on the branch. They even have this diagram laid out in the our NPC code book which would be pretty close to what I am doing if I were to add the clothes washer drain:

But, since the shower is left of the toilet, I figured based on the horizontal order of the fixtures and how they'd need to tie into that main horizontal drain line below, that it was easier to dump the toilet arm into the main stack and maybe better practice to have everything separately vented since it is possible to do so.

For the shower trap I see what you mean now, but I would really like to keep it between the floor joists so it can be insulated. The temps in January and February routinely get below -20C / -5F and I am worried about it freezing and the closer to the subfloor I can keep it, the better. These are the joys of Ontario vs California . I think the vent could be fixed by lowering the trap arm slightly and then running a vent teed off the top of the trap arm instead, but far enough from the trap that it does not create a crown vent?

 

[wwhitney]

That diagram is very interesting, because it has several aspects that differ from my understanding of US practice:

1) The separately vented kitchen sink drain being a fixture that drains through the wet vent; in the US that would have to come in downstream of the final wet vented fixture, I believe.

2) The wet vent being sized at 3" for 4 DFUs; both US codes allow 4 DFUs (maximum) on a 2" wet vent.

3) Fractional DFUs

4) Sizing the entire wet vent based on the full discharge to it from all fixtures, rather than segment by segment based only on how many DFUs each segment is carrying. There's been a bit of debate on that question here, so it is possible I have that wrong.

So, anyway, you should follow the information in your code over anything that I tell you about US codes. : - )

On the shower, aren't the trap and the san-tee in the same joist bay? So you can raise up the san-tee and keep the trap and trap arm in the joist bay. If they can't be in the same joist bay for some reason, you can drill a joist or two for the shower trap arm.

Cheers, Wayne

 

[Jeff H Young]

might be able to horizontally wet vent shower off the drain for kitchen in Ontario?

 

[Jedrek4680]

If I could come up with something that passes IPC, UPC and Canadian code, all the better. I am building in an area without building permits or inspectors so I am technically required to build to code but nobody will be checking. The main concern is good long term functionality.

Here are the Canadian code requirements for wet venting:

The main point for my small setup being WC have to be downstream of all other fixtures.

There is also a section on stack vents:

Based on #4 stating that fixtures are permitted to be connected to a vent stack, I figured it was best to run the WC (4DFU) directly into the vent stack rather than wet venting since it would effectively be vented by the main stack unless I am misunderstanding how it works. In my original drawing it was below since I thought the WC needed to be the last fixture based on 4c).

I had the shower trap going thru a floor joist into the next bay to make more room along the horizontal waste pipe to tee it in:

If I:
1) get rid of the shower vent it would eliminate the up and down jog in the arm mentioned previously, and
2) drop the toilet into the waste pipe between the current main stack and shower...
then it'd be the same as the drawing from the NPC code book with the addition of the washing machine standpipe which also has its own vent like the kitchen, and a 3" waste pipe handles enough hydraulic load

Now I would need to figure out how to do so without adding any horizontal bends in the poop arm

 

[wwhitney]

Based on #4 stating that fixtures are permitted to be connected to a vent stack, I figured it was best to run the WC (4DFU) directly into the vent stack rather than wet venting since it would effectively be vented by the main stack unless I am misunderstanding how it works. In my original drawing it was below since I thought the WC needed to be the last fixture based on 4c).

2.5.4.2 doesn't require you to have a vent stack. And the vent above your combined vertical drain is only for venting the WC, everything else is individually vented. So if you bring the WC in above the other horizontal drain, everything will be individually vented, and there will be no wet venting. The "vent stack" will begin at the top of the WC san-tee, and there will be no fixtures draining into the vent stack.

I had the shower trap going thru a floor joist into the next bay to make more room along the horizontal waste pipe to tee it in:

That's not necessary, you don't need more room along the horizontal waste pipe, not worth drilling a joist.

Why can't you just raise the san-tee to near the top of the joist, and put a street 45 in the top of it to start jogging over your beam? Then the p-trap just ends up where it has to be based on the san-tee height, the trap should still be within the thermal envelope. This is assuming you still want to individually vent everything, rather than wet vent the WC/shower.

If I:
1) get rid of the shower vent it would eliminate the up and down jog in the arm mentioned previously, and
2) drop the toilet into the waste pipe between the current main stack and shower...

Yes, if you move the WC just above the horizontal branch drain, and then move the shower to a san-tee above that, you have a short vertical wet vent of the shower over the WC, but that's totally standard.

Now I would need to figure out how to do so without adding any horizontal bends in the poop arm

I don't understand this statement. If you are referring to the WC fixture drain, what's wrong with it having a horizontal bend?

Cheers, Wayne

 

[wwhitney]

Also, why are you bringing the kitchen sink drain through 3 joists?

One more wet venting option to consider: bring the lav drain into the WC drain on the horizontal to wet vent the WC. Here's a drawing in plan, where the different color lines are different elevations, and the purple circles are vents. Red is the shower trap and drain within one joist bay, and the location of the red circle (which is the stack) is determined by the shower drain location (since you want the trap within the thermal envelope). Blue is just below the joists (at the upstream end), and green hits the stack below blue. There may be little jogs for the vents to get them into the wall over the beam, but I omit that detail.

Cheers, Wayne

 

[Jedrek4680]

2.5.4.2 doesn't require you to have a vent stack. And the vent above your combined vertical drain is only for venting the WC, everything else is individually vented. So if you bring the WC in above the other horizontal drain, everything will be individually vented, and there will be no wet venting. The "vent stack" will begin at the top of the WC san-tee, and there will be no fixtures draining into the vent stack.

It makes more sense when you explain it that way, thank you. I see if the WC is above then it has a direct venting route vs having some interference by being part of a drain the way I had it originally.

That's not necessary, you don't need more room along the horizontal waste pipe, not worth drilling a joist.

I wasn't sure if I could fit both size by side below the same joist bay (they are 16" OC)

Why can't you just raise the san-tee to near the top of the joist, and put a street 45 in the top of it to start jogging over your beam? Then the p-trap just ends up where it has to be based on the san-tee height, the trap should still be within the thermal envelope. This is assuming you still want to individually vent everything, rather than wet vent the WC/shower.

The beam is directly below the sill, the floor is not cantilevered at all, it just creates the need for a jog at the exterior wall below the sill. I couldn't figure out how to draw it in SketchUp but wanted to use a single 45 there rather than 2 90s.

I am now thinking wet venting the WC and shower would be better since it eliminates a vertical vent, materials and labour.

Yes, if you move the WC just above the horizontal branch drain, and then move the shower to a san-tee above that, you have a short vertical wet vent of the shower over the WC, but that's totally standard.

I was thinking of tying them into the horizontal branch drain but the WC would tie in last before the vertical drop down to the septic out pipe. If i stack 3 san-tees below the floor joists I would be getting really close to the dirt and want to keep things tucked up so they are not visible except for the 1 vertical pipe.

I don't understand this statement. If you are referring to the WC fixture drain, what's wrong with it having a horizontal bend?

My thinking was just that it would flow better with a straight run, and since the horizontal branch would be exposed it would be best not to add any bends that might help hold waste that could then freeze between flushes.

 

[Jedrek4680]

Also, why are you bringing the kitchen sink drain through 3 joists?

That was for the sake of tying it into the right part of the horizontal branch since the main stack was in the 2nd bay, shower in the 3rd, etc. Something about that did not seem very efficient to me.

One more wet venting option to consider: bring the lav drain into the WC drain on the horizontal to wet vent the WC. Here's a drawing in plan, where the different color lines are different elevations, and the purple circles are vents. Red is the shower trap and drain within one joist bay, and the location of the red circle (which is the stack) is determined by the shower drain location (since you want the trap within the thermal envelope). Blue is just below the joists (at the upstream end), and green hits the stack below blue. There may be little jogs for the vents to get them into the wall over the beam, but I omit that detail.
View attachment 69765

Now that I understand a bit better how things vent and can enter the stack at different elevations, this seems a LOT more efficient than trying to have the long horizontal branch and drilling a bunch of joists (which probably then requires a bunch of couplers and swearing to get pipes in place so I'd only have to worry about that up top for the vents). I might need to rework my plans, I really like this idea. To confirm I am understanding correctly, are the elevation of blue and green interchangeable since they are both have their own vents and the shower has to be at the top since its using the main stack to vent?

 

[wwhitney]

To confirm I am understanding correctly, are the elevation of blue and green interchangeable since they are both have their own vents and the shower has to be at the top since its using the main stack to vent?

Basically yes. The shower connection is also on top within the joist bay because you want the shower trap within the thermal envelope. Then since the blue drains are shorter overall, they accumulate less fall, so if you start both blue and green against the bottom of the joists (almost), the blue will arrive with less fall, while the green will be lower.

But if it works out better for you, you could bring in the blue below the green. Or you could bring them in at the same level using a double san-tee or better a double combo (since they are already vented). You'd just have to run the green into the corner and use a LT90, instead of cutting the corner with a 45 as I drew.

[Or you could move the up-down (on the page) green drain over a couple joist bays, and have the green hit the blue with a combo before the blue hits the stack. Or you could move the up-down green over to be in line with the red stack, and you could move the blue left-right drain up a bit to hit the green before the green hits the stack. Or . . .]

BTW, the immediate 90 bend I drew in the red line just represents the swivel joint between the u-bend of the shower trap and the outlet elbow, it doesn't represent an additional elbow, as there is no need for one. And you can swivel that any way that is convenient.

Cheers, Wayne

 

[Jeff H Young]

if you dont want to drill 4 joists I think waynes drawing above would work well with exceptin of running washing machine as original. but in any case you have a good plan

 

[Jedrek4680]

Thanks guys. Going to evaluate how much space I have vertically from the ground to my floor and see if I can drop in at 3 elevations. I think it will work well.

The electrician started today and everything is well out of the way of this plumbing except the main stack will have to cross 3 wires in 1 stud bay where the loft wiring went. but that should be no big deal.

 

[Jeff H Young]

i like to put plumbing in befor sparky. its ok if his boxes are in but romex can go anywhere .

 

[WorthFlorida]

A DWV venting guideline. http://www.plumbingpros.com/pdf/dwvents.pdf

 

[Jeff H Young]

A DWV venting guideline. http://www.plumbingpros.com/pdf/dwvents.pdf

Nice Worth Florida! What I like about that info is even though a lot isnt the same in other jurisdictions it gives you a pretty good idea on function. working on existing homes I find things plumbed many differant ways helps troubleshoot

 

[Jedrek4680]

That is a good background on the venting, thank you.

I reworked the design based on the previous suggestions and was able to make it more efficient. The shower vents thru the main stack instead of separately, the WC now wet vents thru the lav, and the kitchen and washer drains run parallel with the joists so there is less drilling thru joists. I would only need to worry about drilling 1 floor joist to bring the kitchen drain across to the main stack, and then a few loft joists to get the vent pipe across.

Can the shower trap arm connect like this with the main stack, or do I need to bring it in down lower with a tee in vertical orientation? If this isn't allowed or it would be better maybe I could use a double sanitary tee to bring the shower and kitchen drain on the left into the main stack at the same elevation. Just trying to keep the shower trap up as high as possible to prevent freezing.

 

[wwhitney]

The shower dry vent takeoff can't be horizontal.

I suggest a double san-tee below the joists to receive the kitchen on one side and the WC/laundry/sink on the other side. Then above that a san-tee, then a pair of 45s to jog into the wall framing. Use one LT90 and one 45 to connect the kitchen to the double san-tee. [You could instead use a double wye, which would be nice if the kitchen side could rise at a 45 until hitting a 90 to go horizontal at the correct elevation.]

US codes would require the laundry to come in downstream of the WC, but I guess we established the Canadian code doesn't? I would think it would still be worth drilling one joist to make that happen, but then I'm used to the US codes.

The tees, and the double 90s to jog instead of double 45s, those are just drafting inaccuracies?

Cheers, Wayne

 

[Jedrek4680]

The shower dry vent takeoff can't be horizontal.

I had a feeling... lol

I suggest a double san-tee below the joists to receive the kitchen on one side and the WC/laundry/sink on the other side. Then above that a san-tee, then a pair of 45s to jog into the wall framing. Use one LT90 and one 45 to connect the kitchen to the double san-tee. [You could instead use a double wye, which would be nice if the kitchen side could rise at a 45 until hitting a 90 to go horizontal at the correct elevation.]

This gets rid of one more hole thru the joists. The double wye would work here (likely better to smooth the flow of solids), with this configuration I have enough room vertically beneath the floor joists for that to work.

US codes would require the laundry to come in downstream of the WC, but I guess we established the Canadian code doesn't? I would think it would still be worth drilling one joist to make that happen, but then I'm used to the US codes.

I posted the wet venting rules from the Canadian code earlier in the thread along with the diagram showing the kitchen sink coming in upstream of the WC. It says under the wet venting rules that "water closets are installed downstream of all other fixtures". The way it reads makes it seem to me that this applies even in the case of the separately vented washer. There are a few other examples provided, but none of them have anything come in downstream of the WC

The tees, and the double 90s to jog instead of double 45s, those are just drafting inaccuracies

Yup, can't figure out how to get the SketchUp plugin to draw 45s. Maybe I'll fiddle with it some more as I think this works well now but could add 45s for the double 90 jogs. It only gives the option for tees at intersections, not tee-wyes or combos.

Does this make sense now with the shower vent moved down and double san-tee tying the branches together?

 

[Jeff H Young]

That looks good only 2 things . Personaly I prefer on the waste stack a 3x3x2 wye for the kitchen , but if the double fitting is available and you like it great its legal ! But the venting for the shower should not be 90s but 2 45s is perfect. Ive Used 90s a million times but for us in upc code its a judgement call and we can get shot down, even though if "nesesary" an inspector can aprrove the 90s