How to insulate bonus room and use of air baffle
I have read many articles on how to insulate a bonus room over a garage. I have a heat run in the attic space behind the knee wall. Therefore, I plan to include the bonus room and attic space in the conditioned space. I want to run 1” inch continuous air baffle from the soffit to the ridge vent and air seal it. I am working with
2×6 rafters and I want to get approximately R30 rating by using 5 ½ high density fiber glass R21 plus Styrofoam (extruded polystyrene insulation) Wallmate R7.5. These are 2×8 sheets slotted for a 1×3 firing strip. To increase the R value I would like to make my own air baffles from ½ polystyrene insulation. This would add R value of 2.5. I am concerned about trapping condensation inside the cavity. Do you know what the permeable rating is for ½ foam board and whether it can be used to create the an air baffle? I have checked with the various manufactures of the foam board, but I cannot get a clear and definitive answer from them.