building code question on plumbing

I'm confused, can you provide more information?

No, yes (w/ the caveat of approval of local Code for the installation)

You'll have to deal w/ the freezing issue adequately, of course if it's above ground in most of US

Absolutely yes, or absolutely no, or absolutely maybe. That's as close of an answer as anyone could come with the paucity of information. If, at some point, you decide to build a real house, you will, of course, have to deal with real people, and not the imaginary people on Usenet. Introducing yourself to the local building inspector/department would be a stellar place to start. They will be able to answer questions about real requirements for real houses. Really.

Are we talking supply plumbing or waste plumbing?

Supply lines on the outside of the foundation would be subject to freezing. Even if you live in a warm climate where that isn't an issue, you would likely need to worry about UV exposure which could make the pipe brittle and eventually crack (assuming plastic pipe).

Properly sloped waste lines would be less susceptable to freezing, but it could still happen if temps are cold enough.

You also need to worry about physical damage if they are located on the outside of a building.

As for the code legality, I'm guessing that would depend on your location. I can't imagine why anyone would WANT plumbing on the outside of a house (it's visually unattractive), but there are several older houses in my area (Washington State) where waste plumbing was retrofitted into old homes and routed on the outside of the building.

Anthony

followup.

I did some calculations on wood deck versus cement pad. It would appear that a simple pad costs weigh less. Not to mention probably taking a lot less time.

Either way - building castles in the air is always fun.