...First, could you explain what a wall truss is in the context of a timber-framed skeleton? Second, what is a thermal diaphragm? And third, what is a cold roof/rain screen wall system?
So if you are talking stem walls or plinths then I'm assuming the insulated wood floor sits on top. Is this a standard joisted floor? Can you describe the wood floor in terms of how its constructed and insulated?
The description of the "egawa (small porch) all around the structure" makes me think of a wrap-around porch, is that what you are talking about? What role does this play?
This sounds great b/c I'd rather actually live in the house and experience what is needed before investing in a backup heat source that may be too little or too much. Can you explain what design features would make it easier to add a system later on? What radiant heat system would you be referring to, is it baseboard-style?
I love the wall truss system, allows you to build super thick, well insulated walls. So, next (obvious) question: what infill would you use? I believe you suggested mineral wool batt, what about densely packed cellulose? Other options?
Do the "ribs" not create thermal bridges across the wall thickness? (I suppose this would apply equally to regular stick-framed walls)
What other layers are there in this wall structure? Gypsum (drywall, yes?) on the inside? Vapour barriers? And what sort of exterior cladding can be used?
So you have a thick wall filled with wonderful insulation - is the idea to make this wall breathable? If not, is the home sealed tight and an air exchanger used?
Wrap-around porch, why is this needed? I confess, I've always disliked them (I totally get why you would want them in places that get super hot). Our winters are dark, grey and dreary and I want as much light as possible streaming in through the windows. And I want to see the sky out my windows! And how does that work with passive solar anyways?