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Climate Zone 7, Canadian Prairies
Closed cell spray foam was installed on the dormer walls (2×4 studs). I added cardboard at the bottom of each stud bay to serve as a stopper for the spray foam. 3″ EPS type II rigid board is being added to the attic side of the dormer wall and roxul mineral wool insulation is being added at the bottom of each of the stud bays below the spray foam. (Photo attached).
Questions:
-Is it ok to butt up the roxul and spray foam? (I am concerned about condensation and being careful not to mix insulation types in LAYERS. In this case I know that I have the correct r value in the 3″ of EPS for my climate zone so it can be layered with the roxul. But my concern is about butting up the roxul to the spray foam.)
-Can I run smart vapor over the entire wall?
Thank you.
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Replies
Mill-house,
I will ask a question to give your post a bump. How much close cell foam did you install (or what is the dormer wall constructed -- outside to inside)?
Mill-house
I'm not sure I'm understanding your assembly or what you are asking.
If I am following you, the plan is to finish insulating the bottom of those dormer stud bays with mineral wool (assuming that is to remain unconditioned attic space on the other side of the wall) and then install rigid foam over the studs to reach your required R-value. Is that correct?
And you are wondering if you need a vapor barrier between insulation types. Is that correct?
Please clarify and let's see if we can help you out.
Yes it’s an unvented, unconditioned attic space and yes, rigid foam will be installed on the attic side of the kneewall and dormer wall.
There are two things I'm wondering about:
1. Is it ok to have the spray foam and roxul butting up against each other in the stud bays.
2. Is it ok to run smart vapor over the entire dormer wall from bottom plate to top plate?