I have a timberframe home installed with SIP panels. (7/8" OSB, EPS foam) The timberframer installed also the SIP's. I would like to install Cedar Siding, 1"x10" planks, 3 sides planed-1 rough side. I will leave a 1" of space between the boards to fill with "Perma-Chink" after to get the square log home siding effect. My ideal installation would be to: 1) install 3" same thickness planks as siding verical as "nail in" 2) all needed flashings etc. around windows and doors. 3) Glue and screw the cedar planks (glue to avoid cupping) Stainless steel screws with head to match cedar stain color 4) Squeeze Perma-Chink" caulk in between 1" space between boards to achieve the "log-home look" But I feel that I should put a barrier on top of the OSB in order to keep any moisture out / away from the SIP-OSB. But by doing that I can not use the glue, which I would like to use to avoid the cupping. Normally I am used to install Tyvek, spacer strips for ventilation and then screw siding in studs. But with the SIP's I am confued. Please advice / give me your opinion. I am living in Alberta / Canada, simular climate as Montana.

You have to have a drain plane. If you glue the siding to the OSB, the drain plane would be eliminated. You could use a product like http://www.stocorp.com/allweb.nsf/stoguard as a paint like barrier against the OSB but it doesn't solve the issue of the drain plane.

I was thinking that a drain plane is not needed. My impression of the SIP is that no moisture from inside the house travels through the wall cavity to the outside, were you would need a vent space then in order to get rid of it, specially if you don't have a siding (e.g. alu / vinyl) what let's moisture through. So when I don't have to worry about the interior moisture, I just have to worry that moisture from the outside does not come through. And by the correct corner / window / door details as well as caulking, that should be avoided. CORRECT OR NOT?

The whole concept of building is to keep the water on the outside. The drain plane is in effect for the failure of the first line of defense. And while you in theory might build a structure that prevents penetration, you won't be able to guarantee that there won't be a failure over time. The fact that materials shring and expand at different rates cannot be avoided. And the simple fact is that you won't meet code without a drain plane unless there is an approved detail for the construction. They apply stucco directly to some types of ICFs. Your problem is that you already have OSB and I would guess you would void the warranty of your manufacturer if you don't install a house wrap.

Not.

Building science professionals are coming to recognize that the reason old buildings didn't rot was not because they stayed dry by keeping moisture out, but because they had so many air passages that when they got wet, they dried out quickly. New house building techniques don't provide for near the air flow any more so now trapped moisture stays trapped. A tight envelope (such as the space between the wall and siding) will always have some air leaks. What happens is the envelope interior air expands and contracts with daily heating cooling cycles and it always sucks in more moisture than it expels, leading to a buildup of moisture in the closed space. Hence the need for a drain plane. You will also find advocates who will argue that around windows, doors, corner trim, siding board ends, etc. the best caulk is no caulk. Build the exterior finish configuration to shed water, not stop water. Accept the fact water will come through any siding system and provide a means for it to safely drain away.