I'm considering having a timber frame home built with the frame being enclosed with the layering of polyioscyanurate panels. After the frame is up, a sheet of OSB is secured to the posts, then a layer of 1.5" polyiso is placed. Then a 2 x 4 is placed 24" OC and a second layer of the polyiso (1.5") is put between the 2 x 4s. Then a layer of OSB to enclose the layering. This system is supposed to give an R value of 22. Anyone ever use this system? Any feedback is appreciated.

Not sure what you gain by doing that. OSB/glue/3" of foam/glue/OSB is quite strong without a 2x4 extending halfway through it. Or if you have other framing for strength (sounds like you do), then it works well without the glue (and without the 2x4).

Foam with some replaced by a little wood will have a slightly lower average R value than foam alone.

jonr:
No glue in the layering. Just OSB (interior) followed by 1.5" foam panel, then 2 x 4s, then 1.5" foam panel between 2 x 4s, then exterior OSB. It would seem that the wall R value of the wall would be less than 21 (3" of polyiso foam panel) since the second layer of foam has a break every 24". Also wondering about cost effectiveness of this method vs SIPs. Thanks.

Before you get deeper into the stack-up of the wall assembly, one has to know what climate zone you are in. Improper stack-ups can lead to moisture issues in the assembly and eventually failure. Vapor barriers on the wrong side, air leaks, inability to dry the assembly, etc. can all lead to problems.

What climate area are you building in?

I'm in zone 5, CT.