Contractor insists air gap between batts and basement brick mean no prob for humidity, with or without polyethylene vapor barrier.
If humidity is accumulating in an air-sealed air gap (humidity coming thru brick), an air gap won’t save you. Surely an air gap is only good if you have air leaks. Imperfections in sealing will happen inevitably unless installers take extreme care, including at electrical and plumbing penetrations, but I could additionally add a pinhole or 1 mm hole to the interior every 6 feet or so. There are no known water leak issues and there is large overhangs with proper detailing so little rain gets to the brick, although some snow can accumulate at the base. Should I apply a water seal over the exterior of the brick+mortar around the bottom say 18″? Would an air gap then make batt insulation + poly okay?
(double-brick / air-gap / batt / poly / drywall, + insulation in rim joist gaps + insulation under the-floor-above at top of air gap, so cold air doesn’t flow over the basement ceiling drywall)
Better with poly? Without poly, condensation would happen on the brick, and may run down and pool at the base, but with sufficient air gap and leaks, condensation would evaporate before pooling became considerable. No weeping tiles or anything similar, so should use exterior-grade wood for bottom plate of wall framing, or add waterproofing to interior-grade bottom plates. With poly, humidity doesn’t pass to cold side of insulation, so there’s no condensation from outward flow. From inward perspective, moisture that comes in thru brick would not travel thru poly but would escape thru leaks as humidity levels seek to be equal.
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