Gabel,
I agree fully with your statement. I think that timber frames have always relied, to an extent, on the siding system for stiffness. I’ve tried to ‘shake’ many different buildings in various degrees of finish to get first hand exposure regarding how flexible or how stiff a frame actually is. Some times I’ll get few guys in the loft and we’ll do the old 1,2,3, shake. Siding and SSP/SIP do stiffen timber frames. Unfortunately, today’s building codes do not provide any clear path to account for this. Using SSP/SIP to augment the timber frame, or provide the full lateral load resistance system, is done. But designing a stand alone timber frame while keeping brace tension at manageable levels is proving difficult for me?

Thanks,
pete