Using Polyethylene as an Air Barrier
Many builders have stopped using polyethylene vapor retarders, not only because they are no longer viewed as a necessity in most climates, but also because poly has the potential to trap moisture in walls and ceilings. Air barriers are now viewed as much more important.
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But a poster at GreenBuildingAdvisor’s Q&A forum wonders whether poly might make a good air barrier in a high-performance building he’s putting up. Minneapolis Disaster has read of successful uses of poly in well-insulated houses with extremely low rates of air infiltration. Plus, it comes in 12-ft. wide rolls that would be more convenient than housewrap, which comes in 10-ft. widths.
Minneapolis proposes to use a layer of poly on outside walls between plywood sheathing and a layer of polyisocyanurate foam insulation; in the ceiling, poly would fall between two layers of polyiso.
Is the plan risky?
That’s the subject of this week’s Q&A Spotlight.