1. Ability to "breathe" through passive rather than active systems.
The concept of "air tight" and then using an "iron lung" (aka HRV or related systems) seemed like a bad idea from the start from my perspective...
Good for big industry and no doubt will stimulate "return service calls" for contractors, but in the way of "good practice and good design" in architecture...I am sorry it fall dramatically short.
"Draft proof" and naturally efficient healthy building practices are my goal...
There is simply nothing wrong with opening a window, if a home is insulated well, to get fresh air when needed or wanted. Venting moisture out of bath space..."may"...be a necessity in some design's however in many the proper employment of natural materials with high "load capacity" for free water should also be part of a system. If I "vent" a bathroom, it is directly within the "shower enclosure" itself which should simply be an open window or vent to the outside. Bathhouses are also a consideration and the use of materials like stone, lime plasters (aka Tadelakt, etc) should also be a consideration.
2. Differentiation between drafts and desirable air movement.
The distinction between drafts and "fresh air" is a matter of making sure that no "unwanted" air is moving rapidly through the thermal envelope stimulating conductive temperature differentials...and...if it does in anyway that the interstitial moisture can rapidly "dry out." Of the modern insulations few at all can beat "mineral wools" and their 150 year old track record...Of natural insulative or mass (aka flywheel) systems many can achieve this as well.
3. Longevity of materials and design.
I have beleive the "wall truss" system will more than match a timber frames design longevity and more importantly also facilitate ease of servicing and/or upgrade/remodel, should that be necessary.
4. Sustainability and economy. The ability to use local resources when possible and and also to use homeowner labor effectively to keep their costs down (when they want to).
Since our "wall truss" are nothing more than "small timber frame bents" with all mortise and tenon joinery, I couldn't think of a more sustainable and economic system to use. We employ "green" locally harvested wood that we usually mill ourselves within the collective group and create "wall truss" that can be if needed be considered fully structural in nature. Some claim this is "overkill" and wasteful...I say, to such "naysayers" that such a view is deeply steeped in "opinion" and does not reflect that actual nature of just being...really well built...
I think that my top choice that I have heard of is a light clay and wood chip wall enclosure.
As Will B. suggested, "wall truss" could more than serve as a armature for this system.
I will note that this is a very labor intensive ($$$) system, and further may better serve for only interior wall spaces to act as a "heat sink" along with the timber frame itself in that capacity. This is why (even though having low R value) log architecture can work very well and creating an efficient structure.
Cobb in general is a wonderful medium, whether in a "dense form" or a "light form" like "straw clay slipping." Both again, are very labor intensive and more in the realm of DIYer and/or very upscale architecture.
If a client has the gumption and willingness to work hard, this "light cobb" methods is well worth exploring...
As for "vapor barriers" I simply will not use them. They are "conceptual" at best and no matter how diligent someone is, moisture always finds its way into the interstitial voids of any wall system with them...and then...can't effectively escape...
Super thick mineral wool batt and then exterior boarding is more than enough "barrier" in and of itself...Combine this with earth/lime/paper plasters, natural paints, jointed wood cladding, etc and there is simply no need to add "plastic barriers or paints."
Like I tell clients and colleagues alike...think of the last time you had a "rain slicker" one...Usually you get just as well from sweat as you would from the rain itself...Few have every tried or got to experience "buckskin" and "thick wool felts" for outer garment...They are still superior an many ways with only a good "hydro fleece" coming up a close second...for get other stuff. As an active Wilderness guide and outdoor professional as well as Timberwright, I like "natural materials" all around...
I also know that there are "smart" vapor barriers on the market by the likes of Pro-Clima, but I haven't looked into it.
Let me know Sean if I can ever help you flesh out the wall truss more, I have designs in Sketchup and I know you (like me) are a "Festooler Guy" and have all you need to make the "jointed forms" of wall truss. You would love them and frankly, nothing complements a timber frame like them...
P.S.
Will B...I have built a number of "Palapa" and "Chickee" over the years...if you have a spot in mind...let me know!!!
