What is the proper location of a vapor barrier in a home in New York State?

Michael Boice

I read a couple of articles regarding vapor barriers and insulation.  I live in update NY, our home was constructed in 1952.  We are adding a full shed dormer with 2x6 walls and 2x12 rafters.  Our plan is to use closed cell in the walls and ceiling - which will have a copper standing seam roof.  Code requires a Tyvek type outer wrap, but we want to consider adding 1/2" or 1" polystyrene to the inside to prevent bridging.  Sheet is then applied to the polystyrene.    

I do like closed cell, the excellerant is worrisome as it is a fairly potent green house gas.. 


thank you, Michael

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