I am renovating an old office trailer into a tiny house up here in northern Alberta.. I have gutted it from its poorly installed fibreglass and bad windows and put 1" silverboard foam on the outside with a 3/4 rain screen and LP smart side.. my concern is I was planning to flash the 2x4 cavities with 2" of closed cell touch n' foam SPF and then cut roxul batts in half to fill. I have read that flash and batt isn't recommended in cold climates because it can cause condensation in the walls.. would having the 1" silverboard outside fix this or should I forget the spray foam and just use the roxul?

Northern Alberta covers a lot of terrirory- can you be more specific? Most of northern Alberta would be ICC zone 7, but at altitude it could be zone 8.

See the light purple vs. the deeper purple in this map: https://www.buildings.com/Portals/0/images/OnlineImages/2012/0712/B_0712_RValue_ASHRAEMap.jpg

In zone 8 climate (more than 7000 heating degree-days, base 18C) in wall assemblies as long as 45% of the R-value is on the exterior of the first condensing surface (where the fiber meets the foam) you won't end up with accumulating condensation issues. In roofs (which run colder than walls, due to radiational cooling into the night sky) it needs to be at least 70% of the total R.

With R12-ish foam on the exterior of R6-ish rock wool you have plenty of dew point margin without needing to resort to interior side vapor retarders (other than standard latex paint on wallboard) even in zone 8.

But it could be an issue for roofs. If your location really more of a zone 7 climate than zone 8 (is it fewer than 7000 heating degree days, base 18C ?) you only need 60% for an unvented roof, and it would be alright. In a 7000 HDD(18C) climate adding at LEAST an inch of Silverboard EPS on the exterior of the roof makes sense (walls too), and would give you more dew point margin where the rock wool meets the spray foam. In fact, skipping the spray foam and installing 4" of continuous Silverboard over the exterior of the walls and 5" on the roof with R4- R15 rock wool in the cavities is probably still cost effective on a lifecycle basis, and would work well in zone 7 (you'd need 6" up top for zone 8).

This is located Near Edmonton Alberta.. climate zone 7. I already completed the exterior but am about to spray the foam for the first time.. I want to seal it up nice and be cost effective. Last year I purchased 3 of the 600 board ft kits to spray 2" in the 2x4 cavities and want to finish it off with roxul. same with the ceiling.. I already added a new roof structure on top with 8" of blown in cellulose. I appreciate your expert advice Thank you!

Is the roof structure vented above the cellulose?

Yes it is vented. it is built on top of an existing roof structure that tapers from 6-3.5" I intend on using the flash and batt as well.

so do you think this set up is going to work? i want to keep the project going and don't want to screw it up!

With soffit-to-ridge venting above the cellulose layer it should work just fine.