Recently, i took on this job of remodeling an attic,  which was partly reframed and and partly demo’d.  Now here is my dilema. The owner is putting in or has hired a contractor to blow in that insulation that expands and then is scrapped off(polystyrene?)  similar to great stuff in a can.  Now this will be a conditoned space, meaning just lived in,  so how does he vent from soffit to ridge if he has this impermeable membrane in the rafter cavities?  Are soffit to ridge vents necessary if the cavities are impermeable by air and water?    Please help