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How many air barriers are necessary?

entomodonata | Posted in General Questions on

I’ve got two exterior walls in a 1940’s brick home gutted down to the studs and am reinsulating them. Wall assembly is as follows:

Brick veneer
Air Gap
Asphalt housewrap
1×8 board sheathing
2″x4″ studs

I’m filling the stud cavities with 3.5″ rockwool, and then using a continuous layer of seam taped foil faced 1.5″ polyiso on the interior of the studs. The drywall applied over the polyiso will also be detailed as an additional air barrier.

Do I need to go through the trouble of taping the seams of the board sheathing? I could see doing this if wind washing of the insulation was a concern, but it seems that affect is negligible with mineral wool. 

3 different layers of air sealings seems to be as belt + two pairs of suspenders, but maybe I’m missing something? 

I also understand that brick can retain some moisture, so perhaps in this case it’s good to allow for some air movement in the wall assembly to allow for drying/balancing?

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  1. creativedestruction | | #1

    It's not worth the trouble trying to tape and seal board sheathing, especially from the inside where framing members are in your way. Consider the housewrap a semi-effective draftstop; windwashing is nonexistent. Do a good job sealing the polyiso and focus efforts on the transition details like how to seal where interior partitions meet exterior.

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