No one in the foam business seems to want to answer what does happen when a roof leak occurs. Every sample of foam I've seen will not allow any water to pass through it. It also forms a very good bond to the roof decking and trusses...they push it as a hurricane resistant feature here in FL. One...roof leaks will occur...two, you'll never know it..until maybe you fall through a rotted deck or a rotted truss collapses. Any foam people want to engage in a discussion about this issue?
Just go outside and look for the missile sticking through the roof after the hurricane and you will find the source of your leak
At least you will still have a ceiling.
Your neighbour with a vented attic will lose his ceiling before the roof fails with a major storm as water will blow up into the soffit vents, saturate your insulation and bring down your ceilings. That is a fact jack and not a 'what if'