Yes, otherwise it won't adhere to the substrate. My Prediction: Installation will be less than perfect and voids will be left between the insulation and roof sheathing. Those voids will allow condensate to occur causing more of the closed cell to delaminate and rot the sheathing. This of course will not be observable until it is becomes widespread...maybe. Even if the installation is perfect, how are they going to stop the moisture content of the sheathing from elevating, when the exterior side of it doesn't have a vapor barrier on it? It could become the successor to EIFS if it becomes popular enough. Maybe it will perform better in a dry climate.