I have been doing a considerable amount of thinking and figuring to come up with a possible Timber enclosure/infill system. I should mention that I do not want to use SIP's. Not because I think they are evil or anything like that, but for a number of other reasons, such as: Do not want the full width of timbers encroaching on the interior of the structure; SIPs seem wasteful and expensive to me, along with the associated problems of off-gassing, etc.; SIPs seem to be contrary to the rest of the structure, that is: a timber frame should be (in my opinion) a structure built to last for generations, SIPs do not seem to fit the bill at all. and there's more.

My idea, in it's current form, is:

Timber framed walls (obviously) normally using timbers of a 9" depth. Between the timbers are placed 2x6 studs 2' on center. It is important to note that the framing timbers are between the studs, and not on the 2' spacing. Sheathing is fastened to the outside on the studs, but not fastened to the timbers so that timber movement will not cause sheathing problems. The sheathing is then covered at least with Tyvek or other housewrap, but possibly also with foam panels.

Now on the inside you have a couple of different options. If you desire the inside wall to be flush with the timbers, then you frame it out and plaster/drywall/panel it flush, probably with some sort of trim piece around the timber edges that will hide any movement. The system was originally designed to have about 3 inches of exposed timber on the inside of the structure, and works best like that. In this case you apply plaster drywall or panels to the 2x6 studs, and apply a wooden trim piece to the edge of the timbers (once again to conceal wood movement. This trim piece can be anything, such as a quarter round or a rectangular piece that sits flush with the inside face of the timbers, and is made of the same wood. Think of this is sort of like door or window trim, which is really there to hide a gap.

Now you have a 5 1/2" cavity inside of your walls, and this is where your insulation goes of course.

One last thing, it may also be beneficial to have a v-groove or a cove on the portions of the timber that face into the wall cavities. The purpose of this is so that if the timbers shrink, any air gap will be convoluted, which discourages airflow to some extent. A V-groove would be the more convoluted path, however it might also provide a weak point where the timbers could easily split. A cove would not create the same weakness.

Now I realize that this isn't going to fit with our drams of a super-insulated home. Really, though, the important thing is whether or not it is as good or better than conventional stick framed wall insulation?

This system is intended to provide a reasonable ALTERNATIVE when price is a major factor, and it is also designed so that it can be reasonably executed by non timber framers. I am a fan of traditional means of enclosing the structure, and things such as straw bales. The thing is not everyone will go for those things, at least not yet, and in order to remain viable we must have a reasonable alternative.

If I could, I would build all frames with an infill system similar to Fachwerk, but that would also be expensive, and would only appeal to a limited customer base (which is not a good thing, especially right now)

So what do you think of this idea? Is it viable? Is it good? Is it economical?