I don't think any hard and fast rules can apply to this discussion.

When I was raising my first timber frame (my house), my friend said wait, you're going to build a whole separate wall outside of the frame? The only way it can make sense is to justify it in terms of the whole open building concept, that the structure is distinct from the enclosure. And I do like that concept, in theory at least. So unless we all build uninsulated barns we've got to deal with insulation somehow.

I've tried infilling between studs, a whole separate wall outside the frame, my very first SIP roof, DIY SIPS with rigid foam, and I've seen and done lots of research on stray/clay or woodchip/clay walls.

There's pluses and minuses and factors to be considered on all of these systems. I've come up with all sorts of design questions in trying to insulate spaces including (but not at all limited to):

-what is really local? Are the SIPS made 100 miles away local? The cellulose from local newspapers with studs from Siberia? How about studs sawn from the site? What if you then sheath it with plywood? Clay from the site? They don't grow much straw in my neighborhood.

-What kind of foundation can I use to support a timber frame and an 18" straw bale? What if they want a full basement? Alaskan slabs? And keeping the base of the wall dry? And they can't afford a stone stem wall...

-What is the real performance of the insulation? The ICF industry somehow gets to claim R48 on their 3" of foam and 10" of concrete. I don't think so. The thermal mass argument needs to be taken with a big grain of salt in New England. If it's 25 degrees outside on the north side of your house for 3 months, and 65 inside, what's that thermal mass doing for you?
I very much like the straw/woodchip clay walls, but I don't think their R-value will ever approach cellulose or foam. I've seen the numbers somewhere, and they are pretty good, but I'm not sure if they'd meet code where I live. As much as codes are a downer, the insulation standards may actually be worthwhile. Maybe. Depends on how uncomfortable you're willing to be.

-How do you insulate the roof? You need LOTS of insulation in Mass. Are you going to put 3' of loose fill straw/clay up there, and how do you frame around that?

These questions go on and on. In summary I guess I'm saying any of these materials can work great, but there are some issues with any of them. I don't think the TF industry standard (SIPS) deserves all of the props they get in the marketing literature, but I also don't think they're evil. I also don't think you'll be karmically reincarnated as a newt if you build your walls with straw/clay and put rigid foam on the roof. It's a spectrum, and there's lots of variable involved--climate, cost, what materials are available, interior and exterior finishes, comfort of the owners, and on and on. And just like every other design problem, you've got to come up with a solution.

Brad

and note I never said anything about batt insulation. I would argue that that stuff should never be used, at least where I live.