Metal Roof – Peel and Stick Underlayment for a vented roof deck?
I am in the process of contracting for a Metal Roof on my current house and have a question of using what type of Peel and Stick (SA) underlayment to use. The house was built in 1986 and is in Zone 6A (MSP). It has a vented roof deck over a conditioned attic containing A/C ductwork. The underside of the roof assembly is plywood attached to the roof rafters and covered with 2″ of ccSPF. The roof vent has continuous ventilation on eaves and a vented ridge. The topside (roof deck) is one-half inch OSB (circa 1986) is currently with shingles. Pitch is 6/12. The AccuRite sensors in the attic show a range of 50 – 80% RH during the winter. For the replacement roof, one of my options is a 138T panel with ASV clips – which hold the metal panels 3/4″ off the roof deck (think rainscreen for a roof). The plan is to remove the shingles and place a peel and stick on the topside of the roof deck. Lots of choices but two example products are: (1) Platinum FT SA (0.035 perm); (2) VaproShield Slope Shield Plus SA (30 perms). The underside of the roof deck OSB is exposed to the vent – so that does provide a path for water vapor to escape if the OSB is exposed to water. Currently, I am re-reading through the BSI material (BSI 038 and CP 1101). Any thoughts/suggestions/recommendation from the GBA experts?
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