Thanks for the input Tim. I should have mentioned one reason I'm trying to keep the wall system in one plane is so that everything can sit atop a 10" poured concrete wall. Another reason is just to cut down on material, although the wall system you describe doesn't add too much more to the mix. And yet another reason is that I like the look of timber and plaster walls much more than the look of the timber frame standing alone inside the building space.

I realize that the timber/plaster interface requires repointing with plaster as timbers move and shrink.

I can see how the wall system I described in the first post might not make for the tightest house in terms of air infiltration. The thing is, here in the hot humid South my main concern is keeping the house cool, rather than trying to keep out our comparatively mild 8 week winters :-). As such, putting time and energy into a "cool roof" system seems more important than building a super tight envelope. At least that's how I'm thinking about the building design at this stage.

Miles