spray foam cathedral ceiling – GreenBuildingAdvisor

We have a 1-1/2 story Victorian with sloping ceilings on the second floor that lead to a flat ceiling with small attic above. We live in climate zone 4C. I mentioned to an architect friend that I was planning to spray, or have sprayed 1″ – 2″ of closed cell foam to the underside of the sloped ceiling portions of the roof deck and use some sort of “fluffy” insulation between the foam and sloped ceiling. I will conventionally insulate the flat floored attic and will run the spray foam up the underside of the roof deck to the intended level of the top of the attic insulation. He told me that in the UK, lenders are denying mortgages to people wanting to buy homes with roofs insulated with spray foam of any type on the underside of roof decks. Why? And am I making a bad choice? I do not want to create an air channel between the deck and insulation under, nor do I want to tear off a new $30K roof that I had recently installed to retrofit continuous insulation above the roof deck.