How to properly insulate a tongue-and-groove ceiling?
I live in climate zone 5B in northern California and I’m finishing a shop building that I plan to heat in the winter. My plan for the ceiling is to cover it with tongue and groove pine. The rafters are 2×8′, 2′ OC that are vented at the ridge and with soffits at the eaves. I’ve installed R21 Kraft faced insulation between the rafters (Kraft side facing the interior of the building).
To minimize heat loss through the tongue and groove, I’ve considered using either gypsum as an under layment or a semi-permeable membrane like Intello. To make a more informed decision, I hope you can answer the following questions:
1. Since I’m using Kraft faced insulation that I’ve stapled to the underside of the rafters, is it worth going to the extra work of installing gypsum or a membrane?
2. Are semi-permeable membranes suitable for ceiling applications and can they be placed against Kraft faced insulation?
3. Can you help me weigh the benefits of gypsum versus a semi-permeable membrane for the application I’ve proposed?
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