can I install kitchen drain pipe inside a
2x4 exterior wall? I live in Massachusetts.if so, can I use an expansion foam to insulate it?Thank you , Noel

Hi Josh

You sure can install a kitchen sink drain pipe in the exterior wall AND, as long as the PTRAP isn't in the exterior wall and the pipe in the wall pitches at the required 1/4" pitch per foot of pipe then there is absolutely no reason to insulate the pipe!

Is the sink properly vented?

Be sure to add nailing plates over any pipes that penetrate studs and you should be all set!

Mark