What is the proper location of a vapor barrier in a home in New York State?
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..
thoughts?
thank you, Michael
We aren’t fans of spray foam at all, in part for the reason you mention about the potential toxicity of blowing agents, but also that the inevitable day that you addition is deconstructed in the future, all the materials will have to go to a landfill whereas if you did it with batt insulation both the batts and studs could be reused.
About the toxicity, yes you are wise to consider that. Here’s our page all about it –
Spray foam insulation - is it a good green building material or potentially toxic?
But if you do use it, the foam itself acts as the vapor barrier so no other would be required. And yes, there would be no problem adding more rigid insulation to the outside. You can find Aspenite (OSB) with an inch of EPS foam attached to it which will save you a bit of effort and time installing.
Thank you Mike!
I did not give de-construction a thought, but in a future far far away, someone else may decide to removate my home.
To clarify, placing the rigid foam on the outside wall is perferred - which is what the OSB/ESP does. What happens if the ESP is on the inside the a ceiling or wall? I might have thought that keeping the condition air - heat or AC - from penetrating the wall system might be the way to go? And this is really a learning question. Thank you!
Michael