I am contemplating screwing 2x10" fir shiplap on SIP panels as a vertical siding for a timber frame. I am considering fastening the siding with screws directly into the SIP OSB panel without a nailing or furing strip to reduce the distance from the panel. Although a 1x nailer is conventionally used, I question whether it adds any strength to the siding structure since it itself is fastened to the SIP panel rather then to a bearing stud as in conventional structures. Has anyone tried this, and what has been your success rate if you have?

Thank you,

Tom,

the furring strips are not to improve the strength of the siding!!!!!!!!!
Rather they provide an airspace between the siding and the panels so that any water, be it rain(especially with shiplap siding or board and batten) or vapor from the house can run of behind it instead of being trapped between the two layers and cause rot.In your case I would recommend to install vertical strips and then horizontal to which you will nail the siding.If you only install horizontal strips you would create a space but the water cannot run of. That is why you need the vertical ones also. Of course that will bump the siding out a least 1.5 inches but it is a save installation for years to come.

I agree

gabel

Thanks for the comments. I have 4' eave and gable extensions that give reasonably good protection against rain fall off and house wrap over the panels. I am also at 7000' elevation in a relatively dry environment where winters are long. Thus rot conditions are not severe. I am also under the impression that vapor penetration through the SIP is limited by the nature of the structure. In addition, I have an air exchanger. But your points are well taken and appreciated.

Tom,

you are right. The vapor transmission through the panels is small and a lot slower then with conventional framing but it is not nill!! Espsecially during the heating season when all windows and doors stay closed.
Air exchanger is good. 4' overhangs are very good also. But the bottom of the siding will still get rained on.