We are located in northern NJ. We are starting an energy retrofit. We will have 3” mineral wool on the exterior walls. For the exterior roof deck, should we go with polyiso. It is spec’d at 4” (2”+2”) polyiso with staggered joints. Moreover, there will not be spray foam on the interior roof deck (only r19 batts). The roof is unvented. Singled asphalt roof will be the roof material. Is the existing r19 sufficient for the interior roof assembly?