Tub to shower conversion drain issue

[NWCherokee]

I am replacing a second floor existing tub/shower and was going top put in a new tub but wanted to look into what it would take to convert to a stand alone shower and after removing the tub surround I realized that I have just a 1 1/2" drain line to work with. It continues as a 1 1/2" line horizontally to the vent connection and beyond horizontally then down so certainly no easy replacement. So I then looked up section 408 in the 2018 WA State Plumbing code and it says this:

So it appears that the exception may allow for this (with AHJ approval) so the code seems to believe this is acceptable with the correct condition of one showerhead with 2.5gpm or less. I was looking at a prefabricated base with a 3.5" curb so there will be some water retention ability, but my ask is this:

Just because I may be able to do it, would it work well? Anyone have experience with using a 1 1/2" shower drain?

 

[Breplum]

I happen to live in a 50s house with an original tile shower. It has a copper 1-1/2" drain tailpiece with a cast iron p-trap.
It drains perfectly well, even with a somewhat drilled-out flow-restrictor. Never ever builds any pool of water in my 27 years of regular use.
Copper is wonderful as it is somewhat anti-slime bacteriostatic and stays naturally clean. Steel and cast iron, however tend to accumulate build-up badly over the years.
So beware of potential different experience on your part.
As a contractor, I would absolutely NEVER participate in a remodel for a customer that does not address the pipe no matter what.

 

[Sponsor]

 

[Breplum]

Good luck and let us know how you get it done.

 

[Jeff H Young]

I way prefer 2 inch drain on the shower , many testimonys of 1 1/2 working fine 30 years 70 years . If its all good pipe and a hardshipo to up the size to 2 inch Id have no problem following the code as read with AHJ approval. Totaly agree with addressing the pipe with the owner and or inspector. I wouldnt convert a tub to a shower on 1 1/2 without asking them either, plus its a sizeable change order and better work
If you have a Galvinized trap arm Id really advise updating this section of piping , If its ABS Id be pretty comfortable

 

[Tuttles Revenge]

We convert tubs to showers and use the 1.5" drains all the time with the prescribed shower flow restrictions.

You're going to need to move the trap location to accommodate the shower pan regardless, so you'll have the ability to do as much as possible to clean the drain while its open. But also assess whether its feasible to increase the trap arm size to 2" as well.

 

[Jeff H Young]

I dont do it all the time but have and its not an issue even have code backing it up (with aproval) if all the walls are opened up then Id very much advocate running 2inch