shower drain

I really need your help

I converted a tub/shower combination to a shower-only on the second story; I'm ready to do the floor. Here are my questions:

I have an existing 1 ½" ABS drain, which I traced to where it goes into the sole plate on the 1st story. It seems impossible to convert this to 2†b/c it appears that it remains 1 ½ as it goes into the slab. I understand that 2†is required by code. It will not be inspected, however. Am I going to experience any drainage problems b/c my drain will remain 1 ½"?

If it’s possible to leave the drain at 1 ½, my second questions is this:

Should I use a 2†trap or 1 ½†like the original configuration? Naturally whatever size trap I use it will be connected to the 1 ½†pipe


thanking you in advance

I would use the 2-inch trap. Reduce it with a female adaptor, not a male bushing.

Opposite view.

Although 2" pipe diameter has been Code for about fifty years, it is still a well-known fact that shower water will get down a 1.5" pipe too. It used to be Code too. There were good reasons for the Plumbing Code to require a larger diameter pipe, too. Although I won't be the best person to explain it.

There are many plumbers who will tell you that it is a bad idea to decrease a pipe diameter at any point for any reason. Causes blockages too easily. Just let water flow down a pipe of the same diameter through its entire length. My Master Plumber who I paid full rates to, decided to give me a new 1.5" p-trap and pipe after removing the old 1.5" p-trap and pipe, as he said I didn't have room for a 2".

How many feet long is the distance that you will have a 1.5" pipe? This is important. Two feet? Three feet? Twenty feet? Thirty feet? This will make a difference as to whether the 1.5" diameter pipe will do the job "adequately", or "barely at all".

David