Shower drain size

I've read here for years that "the codes" require a minimum 2 inch drain for showers. Yet when I look at the code for my state, the minimum trap size specified for a shower is 1.5 inch. That's based on the IPC, and can be seen here:

http://publicecodes.citation.com/st/ny/st/b900v07/st_ny_st_b900v07_7_sec009.htm


What am I missing?

I'm not a pro, but I've never seen a shower pan, tray, or stall that did not have a 2" outlet, and the code you quote says under note d, "Trap size shall be consistent with the fixture outlet size" So, as a practical matter 2" may be the only solution, even though the code says 1-1/2" as a minimum.

Interesting, the 2007 Florida Plumbing Code says the same thing. Won't mean that I'll start specifying shower traps as 1-1/2". I was taught that the reason behind 2" vs. 1-1/2" for tubs was that tubs, by design, have somewhere to hold water.

I heard that tubs have more ability to "push" water since they hold a mass.

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Which is more "lore".
Where are the facts?
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Any shower drain can be made with a 1.5" opening, and anyone can glue a reducer into a 2" opening, so the fixture itself takes a 1.5" drain.

When all is said and done, I find the 2" diameter requirement for showers to be overkill.

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I'm surprised that after many years of searching, I've never seen an internet comment from an experienced Master Plumber telling me how Code changed over the years.

I'm 100% certain that a 1.5" drain line used to be Code everywhere, for showers. I'd like to know what discussion went into voting for the new size, 2" diameter.

In Canada a 1.5" drain line is still permissible for a shower. Everyone says so, but I've never seen it in writing.

Having said all this, of course, do not decrease any drain line in the direction of flow. The trap size has to be the same as the drain size. Many people conclude that a 2" trap can be reduced to a 1.5." pipe after the trap. Use a 1.5" trap if the drain line is to going to be 1.5" diameter.


I'm not a plumber. Since this is a discussion forum, I'm posting this here as part of a *discussion*; I feel that this forum is the right place for this discussion.


Code has changed over the years and will continue to change in the future.
I'd like to think I'm helping to air out the issues which leads later to clearing up confusion about 2" shower drains.

Imagine all the people who have been forced to do a lot of extra work for no reason !! When a 1.5" drain already plumbed could have been used, they ripped it all out and put a 2" drain in.
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There isn't any confusion. You can't reduce the size of any fixture drain, and you can't buy a shower with a 1-1/2 drain. So, showers must have a 2" drain.

Will a 1-1/2" trap on a 2" fixture drain work? Sure, but it won't meet any code that I know of.

geniescience said:

Code has changed over the years and will continue to change in the future.
I'd like to think I'm helping to air out the issues which leads later to clearing up confusion about 2" shower drains.

Imagine all the people who have been forced to do a lot of extra work for no reason !! When a 1.5" drain already plumbed could have been used, they ripped it all out and put a 2" drain in.
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Just to add to the discussion - code here in FL used to be nothing less than a 2" waste line in the ground, now they accept 1-1/2". Should I change the way I design? I don't believe I will, but will likely have to make revisions for a contractor who wants to use the bare minimum from time to time.

code

The problem is you are using the words "code" and "IPC" in the same sentence, which is an oxymoron.

Many people are adding multiple shower heads.

Some hotels I stay at have three heads.

I don't think I would want to start using 1.5" drains, when the 2" drains are having a hard time keeping up.

tlarson said:

I'm not a pro, but I've never seen a shower pan, tray, or stall that did not have a 2" outlet, and the code you quote says under note d, "Trap size shall be consistent with the fixture outlet size" So, as a practical matter 2" may be the only solution, even though the code says 1-1/2" as a minimum.

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I believe the notes apply to the particular boxes in which their respective letters appear in the table. Is there written interpretation/guidance to the contrary?

Terry said:

Many people are adding multiple shower heads.

Some hotels I stay at have three heads.

I don't think I would want to start using 1.5" drains, when the 2" drains are having a hard time keeping up.

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I certainly agree that anyone putting in multiple showerheads or doing anything that exposes the full drainage run would be foolish to put in anything smaller than 2" drains. The context where an accurate statement of code requirements seems important is when someone is retrofitting and really would have a difficult/expensive time running the new 2" line to replace the existing 1.5 inch. My showers have 2" drain lines, but in reality, I think an unobstructed 1.25 inch drain could readily handle the 2.2 gpm (U.S. legal max) of modern showers that's coming out through a hole that's maybe a quarter inch in diameter, albeit with 60 lbs. of pressure moving the volume along.

Good advice based on years of experience that's passed along by an expert tradesman is invaluable. There is no reason to try to enhance it by mischaracterizing it as a code (legal) requirement when it isn't.

Don't any of you plumbers get annoyed when people try to tell you things are "the law" when they aren't? Like the idiots at health insurance companies that say the medical privacy law HIPAA won't let them mail out blank forms without confirming you identity with 20 questions.

geniescience said:

In Canada a 1.5" drain line is still permissible for a shower. Everyone says so, but I've never seen it in writing.

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In Canada, the shower , bathtub, laundry sink, kitchen sink, has a rating of 1 1/2 fixture units per compartment. It is permissable to have up to 4 fixture units to a 1 1/2 horizontal drain pipe (Only in Canada that I am aware of). So , the shower pan is considered as 1 compartment of 1.5 fixture unit , thus allowing for a 1 1/2" inch trap.. This of course, is for residential application

hj said:

The problem is you are using the words "code" and "IPC" in the same sentence, which is an oxymoron.

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So IPC stands for International Plumbing Conundrum¿