Hello!
I have found an immense amount of information on this website but I am having an impossible time finding anyone in the area that will actually follow the building practices. I live in Eastern North Dakota which is right on the line of a 6A or 7A. 

My plan is to attach a 3 season porch to my current residence and then on the other side of that will be a building for an indoor pool. The 3 season porch will serve as a “buffer zone” between the pool building and the current residence.

I know the best solution is to follow PERSIST or REMOTE building practices for the walls and ceiling but as I mentioned finding someone to follow these practices is not an option that I have been able to find. 

I am considering the following wall and ceiling structure as an alternative and I would like to know if anyone has any advise. I also realize that I will need to maintain correct temperature and humidity in this space. I am planning for about 85 deg and 50-60 % RH. 

Walls: 
2X8 top and bottom plate with staggered 2X4 24″ on center.
From inside to outside:
5/8 sheet rock
4″ closed cell spray foam on backside of exterior sheeting (gap of approximately 3″ of air between back side of Sheetrock and front of closed cell spray foam)
7/16 OSB
Tyvek
Steel Siding
**I have considered adding ICE Dam roofing material on the bottom of the wall between the outside sheeting and the outside 2X4 wall. It would fold over and sit on top of the 2X8. If any condensation did occur it would protect the bottom 2X8 from any moisture. **

Ceiling: (flat ceiling inside with a roof that has a 6/12 pitch)
Option 1. Closed Cell Spray foam 2″ on the back side of the ceiling sheetrock and blow in cellulose material on top of that until we get to R60
Option 2. Spray foam underside of Roof Deck with closed cell spray foam. 

Any and all suggestions on a better design or any advise on the amount of insulation required would be greatly appreciated.

Thank you in advance!