IRC --dwv through return air

[howard01]

Master bath remodel.

I was told that-under IRC- I could not run a lavatory drain line (horizontally) through a stud bay that was being used as return air duct (no metal in duct just open bay air return). I could not find any prohibition for this in the IRC. I found the section on limitations regarding penetrations---but did not see anything that would not allow me to run the pipe (1.5") through the this stud bay.

If you could point me in the right direction i would really appreciate it.

Thank you

 

[MicEd69]

First, running piping or electrical in any ductwork, either fabricated ductwork or the use of the area between the studs and drywall, is poor practice.

The IMC specifically mentions "Materials within plenums", but I couldn't find a similar paragraph in the IRC. However, the IRC mentions linings with the same requirements as to the smoke developed index. That being not anything over 50 shall not be used. PVC has a smoke developed index of 900. So, if you are using PVC drainage piping, you cannot use it within a plenum according to the IMC, and it would be inferred that it would not be allowed under the IRC. ABS has a flame spread index of over 200, so that would be worse. I assume you might be able to use copper pipe if you could get by an inspector.

2021 IRC


2021 IMC

 

[howard01]

thank you for all your insight---very helpful