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Community and Q&A

Air Barriers and Insulation Types

patrick1 | Posted in General Questions on

I understand the reasons why batt (and more generally air permeable insulation) needs to be surrounded with an air barrier on all six sides to have its maximum effectiveness.

Why doesn’t this apply to blown in attic insulation?

Also, do the r-value ratings for loose-fill insulation account for the lack of air barrier on the top side of the insulation?

Why aren’t there ventilated attic designs that create an air sealed (on all sides) cavity on the attic floor for insulation?  One could imagine creating such a cavity with OSB or maybe a membrane like Intello Plus.

Would the top-side air barrier pose an increased risk for condensation?  …in the same way that an imperfect interior air barrier poses condensation problems in a thick double stud wall?

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  1. Expert Member


    Blown in cellulose doesn't lose much R-value at all when not enclosed. Fiberglass batts lose a bit more to wind-washing., but not enough to worry about. I would of course diligently air-seal any assembly, but not to protect the insulation.

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