Vent Stack distance from Tub

[watercamper]

Happy Holidays to all. I moved my bathtub so that I can put in a separate shower. This is a clawfoot tub with a 1.375" diameter drain.

Our Idaho code requires 3'6" for this horizontal distance between the vent and the tub. This is 1.5" drain pipe & 1.5" vent pipe, all per code. (for info, right after the Y (T?) at the vent, the pipe diameter goes to 2"). I looked at the various diagrams to determine where to measure this distance and then measured mine. I am 6" over.

What ramifications can I expect for this extended distance? My engineering mind says nothing. The tub is not allowing as much water to pass through due to it's drain size so less water flow = less need for air. Do you think an inspector would let this go? (Probably depends but I'd like your opinions).

To remedy the situation, can I re-plumb the horizontal run with 2"? (Code allows 5' for 2" diameter & a 1.5" vent. I would still have to reduce the connection down to 1.5" at the tub connection.

 

[johnjh2o]

Code requires a 2" drain for showers.

 

[frodo]

please provide a sketch or better yet a picture of the tub , and the shower drain piping from the vent to the fixture

 

[watercamper]

Somehow I seem to have misled you guys. The drain is for a clawfoot tub. I have a separate 2" drain with it's own 1.5" vent for the shower.

I've attached 3 photos. You are standing on the first floor looking up through a hole I cut in the ceiling to access the plumbing on the second floor. You can see the left end of the horizontal drain in photo #1. At the Y (T?), the 1.5" vent goes up and the 1.5" drain from the tub transitions to 2" (to the left). Photo #2 shows the right side of the drain where the P-trap is and the penetration up through the floor. That is all 1.5" ABS of course. The third photo is of the tub. It has 1.375" diameter drain pipe. There is an oversize rubber washer that allows me to make the transition to the 1.5" pipe.

Table 10-1, Chapter 10 of the Idaho Plumbing Code, Traps and Interceptors says: for trap arm pipe diameters of 1.5", the maximum horizontal length of the trap arm is 42". The guy at the plumbing supply store (not Home Depot) where I buy my plumbing supplies confirmed this when I asked him. He had to look it up on his cheat sheet.

I wasn't sure where to measure the trap arm so I went searching and found this: http://www.klickitatcounty.org/building/FilesHTML/pdf/plmbghandout0411.pdf. The top right diagram on page 3 showed me how to measure the trap arm. Mine is 6" over or 48".

As you can see, I already had all the material so I decided to install and test the tub. Everything works just fine. It drains just like when it was attached with a trap arm length of 18". I just don't meet the code.

I know every inspector is different but would this be a show stopper? What would be my options to make it right? I can think of at least 2 options. Change everything to 2" diameter. Doable and economical if needed. Hire a professional engineer to do a calculation showing that the flow from the 1.375" drain is less than the 1.5" diameter and therefore the amount of air required is less, etc., etc. But, I don't have the money for that. ( I got this idea from the code).

But, maybe I'm interpreting the code incorrectly and the plumbing guy is wrong. So, that's what I'm looking for from you experts. Thanks!

 

[phishfood]

If I were an inspector, I wouldn't worry too much about the extra 6".

But, if you were to cut out the double 90 offset, use a coupling to extend the run, and then a single 45 degree bend pointing at the Ptrap, you would have a much better install. And would get rid of most of the 6" of length in question.

 

[watercamper]

Thanks Phishfood! I installed the drain first then a couple of weeks later, the supply lines. I then realized that my drain installation didn't need that many bends. I'll rework it like you said after I finish the sinks and shower.