I have seen a couple of pictures of unfinished cedar siding. I think it is untreated, although when I mention it to some contractors they seem to almost faint: how will it keep water tight? is one of the questions. Now, I don't think that the siding is supposed to be a moisture barrier, just a barrier for direct impact. I think it is just like the stucco layer: it is really meant to be permeable and it is important to make sure water has a way out on its backside. But I am really just guessing and going from pictures; hopefully someone will set me straight if need be.
What I like about the unfinished cedar planks is that they change hue: they are silver in dry sunshine and almost black when wet.
This is where a knowledgeable architect might come in handy: helping on all these materials questions, and finding all the cool things that I only find when they are part of my "Danish heritage."
BTW, I just realize that the siding on parts of the Googleplex looks like raw cedar; wonder if I will be tired of having cedar around me all day long, all week long.
URL for the pict above: www.kentinternational.ca/
