You can certainly make a TF meet PH standards, primarily because the shell is 'isolated' from the frame. We've done a few now, all with different enclosure methods (and mostly not SIPs). Timber frames that are insulated tend to be structurally redundant, and that is with or without PH standards. Basically just pick your favorite building assembly(ies) that don't use foam and wrap your frame. Or do a hybrid. For walls it could be wood fiberboard, double stud walls, various wall 'trusses' with cellulose or mineral wool. For cathedral ceilings, stick scissor trusses might work, again wood fiberboard, or we sometimes do deep I-joists (over the TF), vented and dense-packed.