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Old 09-02-2010, 12:53 PM  
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Default Exterior wall insulation using reflectix and creating air barrier

I've got a cape cod in northern virginia and I'm redoing the insulation on the exterior walls. The existing insulation is kraft w/ about an inch to the drywall and offset from the siding about a half inch. I was hoping to replace the insulation w/ non faced insul and then put in the reflectix as stated in the reflectix instructions.

My boss who does a lot on his house said the primary thing to do is stop airflow so he suggested using aluminum tape along the edges of the reflectix and wrap the tape around the studs to create an air seal. In doing this I'll have about 3/4" air gap between the drywall (I was planning on green board just for overkill) and the reflectix barrier. He said that the air inside here should be roughly the same temp as the inside provided the tape seals correctly and I shouldn't have to worry about condensation inside this gap. Also he said wrapping the aluminum tape around the studs is fine since the outer edges of the studs can breathe.

My questions are
A. Since the siding is offset from the stud walls should I not risk putting in the non-faced insulation and stick w/ kraft? There are some thin strips I can use to hold it in place but the kraft siding held it in place before. Since I can't place it directly on the boards holding the siding I don't want it to fall down and also want to make sure any air needed to breathe remains intact (I have no attic vents or soffits along the gutters, just at the roof peak so I assume this was used instead of vents). Reflectix specifically says not to use kraft insul for this type of application. I can try to put the styrafoam offsets inside to keep both airflow and hold the insul off of the siding board. Should I scrap the reflectix idea entirely because of this?
B. Was it a good idea in the first place?
C. if I nailed super tiny, virtually unnoticeable holes at the top and bottom of the drywall to keep the temps inside this gap consistent, is that overkill?
D. Is the airflow too low once I install the reflectix to even concern myself with taping up the sides to completely seal it off?

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