SIPs or nailbase with spray foam?
I recently read an article from Building Science Corp regarding unvented ceilings. If I understand it correctly, if I use SIPs or Nail Base as the main insulation/structure of the roof, I can also add closed cell or open cell spray foam on the underside of the roof to increase the insulation. Is this correct? Is one foam better than the other? Could you also use any other type of insulation on the underside of the roof? I thought if you used insulation on the exterior of the roof, you needed to use an insulation that would allow the ceiling to dry inwards. I guess I am a little confused. Thanks for your help.
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