Struggling to find the right insulation contractor and approach
Last year I purchased late 1970s house in south central PA with a large unfinished walk in attic space which I am planning to insulate and begin finishing in the coming year. This space has since also had a Mitsubishi air handler and ducting installed behind the kneewalls, making it all that much more critical to get insulation in.
The current assembly is as follows:
– Open fastener steel roof
– 1×4 Purlins
– 30# roofing felt
– 3/4″ plywood
– 2×6 rafters
The roof pitch for the ESE roof is ~6/12 while the WNW pitch is ~11/12.
Due to the lack of rafter depth and limited ceiling height at the low end of the ceiling, creating an unvented assembly is the only practical approach to achieve a reasonable R value (other than re-roofing and adding exterior foam).
Based on the research I’ve done it seems the best balanced approach between safety and cost would be to use a ‘flash and fill’ or ‘flash and batt’ approach with ~2″ of closed cell spray foam directly against the sheathing. Unfortunately even just 2″ of spray foam over approximately 1700sqft of roof deck ends up being quite expensive.
So far I’ve not had great luck with finding the combination of insulation contractor and approach that I trust completely while also remaining financially viable. The most recent contractor I spoke to proposed simply using fiberglass bats in the joist bays even after I voiced concerns (ugh!).
Another contractor who performed an energy audit on the home last year has strongly advocated for simply using 3lb/ft^3 dense-pack cellulose on the basis of it’s cost effectiveness. I know this approach has been used successfully in some areas, but there is no doubt based on the research that it is inherently more risky.
My questions at this point:
1. Does the existing assembly have any outward drying potential, or is it effectively nil due to the metal roofing?
2. Assuming there are no penetrations, why would adding a continuous vapor barrier (or even carefully sealed rigid foam sheets) under the rafters not be sufficient to prevent issues resulting from interior humidity?
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