I know here in Maine, it's against code.

I live in Ohio and according to my contractor, it was against code. The sink is against an exterior wall, but the water supply lines come up from the floor but not in the wall--I cut a hole in the bottom of the vanity so it could slide "around" the water supply lines. He wouldn't recess a medicine chest over the sink either because there would be no insulation between the back of the chest and the exterior wall. For the same reason, I was restricted from putting a niche in the back wall of my tub. But--double check with your building department--you might be able to do something creative with their blessing. Hope this helps.

It must not be against code in Oregon, because my toilet, sinks and one shower head are all on exterior walls. Must have to do with cold vs. mild climates.

So I called my county plumbing inspector this morning, and he said it WASN'T against code to put the supply lines on the exterior wall, but he gave me one of those "but you might be asking for trouble - like if we got another blizzard of '78" responses. After a little conversation, he said it would probably be fine if I insulated the pipe well.

He also said that some people will tie into the heating duct and let some warm air flow into the wall area with the piping. I don't think I really want to get into that, however.

I'm going to talk to a couple of plumbers (one being my wife's uncle) to get their 2 cents on this.

In my area plumbing can be put in an exterior wall, but as you've been told, in freezing climates it's not a "best building practice".

I normally do what others have mentioned, which is bringing the plumbing up through the floor and in a cabinet back instead of through an exterior wall.

If you have to do it, if able pull the plumbing towards the interior side of the stud bay.

Is this 2x4 or 2x6?

Remove any insulation from the bay. Toss the fiberglass if that's what is there.

Add 2" minimum (more if able, it's about R-7 per inch) of rigid polyiso insulation between the plumbing and the exterior sheathing, not just behind the plumbing, but from floor to ceiling. Cut it about a half-inch less in width than the stud bay is wide. Set it in place. Then use canned foam to foam the gap between the sheet of polyiso and the stud. That'll lock the polyiso in place.

If you've pulled the plumbing closer to the face of the studs and or wall plates, get a few metal plumbing protection plates and nail them to the faces of the studs/plates where the plumbing passes through the framing members. That'll protect the plumbimg from screws/nails during drywall/cement board installation.

Mongo

Mongo
I'm not in the wall yet - but I believe it should be 2 x 6. This is for a shower head, not a cabinet. Thanks for the advice. I will take it. Definitely worth a little more effort to avoid a ruptured pipe.
thanks!

Mongo - one other question - is rigid polyiso insulation available at the big box home improvement centers? I've seen rigid insulation there - but not sure if that is the same thing you are talking about.

Thanks! (again)