View Full Version : ONTARIO 1 1/2" shower drain??

07-12-2012, 09:18 AM
Renovating master bath on 2nd floor. Just ripped up a floor only to discover that the original shower drain is 1 1/2". House was built 1987.

Question: Can I proceed to install shower with 1 1/2" drain? I always thought showers required 2" drains. Thoughts?

Edit: Turns out OBC 1992 Table permits 1 1/2" drains for showers with only 1 head. Am I reading this right?


07-12-2012, 09:22 AM
If it is not being inspected, which I assume is the case, you can do anything you want to. And even if the code DOES permit it, that is a "minimum standard" and you may NOT be happy with the results some time in the near, or disant future.

07-12-2012, 09:54 AM
If it is not being inspected, which I assume is the case, you can do anything you want to. And even if the code DOES permit it, that is a "minimum standard" and you may NOT be happy with the results some time in the near, or disant future.

Not interested in doing anything I want to. Am interested in doing good work, and understanding physics behind code. Thanks for your reply though.

Did you read my original post? Original build has 1 1/2 shower drain. Was surprised to see this.

Anyhow, I'll assume shower with 1 1/2 drain limits the number of shower heads, and lends itself more easily to clogs.


07-12-2012, 11:20 AM
I can's speak for Canada, but here in NJ 1 1/2 is allowed if there is 1 shower head. I understand the concerns that some may have. However, it would seem to me that if it has worked OK for 25 years it should not be a problem.

Gary Swart
07-12-2012, 02:19 PM
As I understand the reasoning behind the 2" drain requirement is this lessens the chance of a clog which would result in an overflow. In my opinion, your drain falls in the grandfather clause, so I would leave it. New shower heads are supposed to be limited in gpm, so there is little chance of a problem. We got along with 1-1/2" shower drains for many years and mostly without problem.

07-12-2012, 04:01 PM
Code allows it in Canada, and there are millions of places with shower drains that size. It is much better to have a larger one, but people are generally happy with what they have. The reasoning for the larger drain is to ensure if you accidentally stand on the drain or drop the washcloth, you might notice it before it overflows the shower curb. It is also necessary if you have a high flow or multiple showerheads. Showerheads meeting current codes are pretty low-flow, much less than those of old which helps, too. Most tubs are 1.5", and many are used as showers, but they can hold a LOT more volume than a typical shower before overflow, AND they have a secondary, overflow path down the drain that usually works.

07-13-2012, 05:27 AM
1-1/2" is allowed in the OBC...with 1 shower head, and is common practice in Ontario

07-13-2012, 07:23 AM
1) Thanks to all for the input.

2) Other option is to tie shower drain to toilet drain using a 3x3x2 low heel, or 3x3x2 side inlet. (See image below.) If I understand correctly, this complicates matters, as it will require a vent for the new shower drain (pls correct me if I am wrong). Further, the only feasible way to vent the shower drain would likely incur a downhill slope. Note that slopes are not to scale in the image.

That said, the existing vent was formerly an LV drain and presently has no fixtures upstream from this diagram. So, worst case, backed-up shower vent would drain down the old LV drain. Still, it's ugly and likely not code. Pls comment on any other concerns over this option.

Thanks again. Feedback is greatly appreciated.


07-13-2012, 10:24 AM
You can't vent using a down hill slope.
If the shower vent was tied into a lav waste and vent, that would work. The lav would wet vent the shower. The lav piping needs to be 2" for it to work as a vent. And it has to grade up, not down.
The drawing above wouldn't pass anywhere.

If you go with a 1.5" shower drain and vent, you can't wet vent it.

07-13-2012, 10:40 AM
Thanks Terry.

07-13-2012, 11:40 AM
from your drawing, why not keep the new vent (yellow) sloped properly and tie into old lav vent above floor, or above FLR of lav if its still to be used for lav

07-13-2012, 12:00 PM

Exactly what I was thinking. Trick will be making all this happen between joists. Right now, am planning for yellow vent to go right instead of left, through a joist bridge, then up a wall cavity about 8" away. From there, clear run to attic.

I will follow up with diagram.

07-13-2012, 12:48 PM
ITEM A: Yellow vent drops into 2" shower drain from the top
ITEM B: Run is 45 deg to shower drain

Does this eliminate horizontal venting?