Spray Polyuethane Foam (SPF) is a great insulator and considered to be a very "green" roofing material. But it is the coating over the foam that determines it's life. SPF left un-coated will degrade very quickly in the sun's rays, with-in months. So it is the coating that will determine the ultimate success or failure of a foam roof.
A foam roof is a sustainable roofing system if the coatings are maintained and regularly inspected - once every year or two. Bug's, bird's, and gravel can make holes in the coating, allowing sun and moisture to begin to degrade the foam. If the foam degradation goes too far, the foam will have to be torn out, prematurely. So a superior coating - one that is strong, and flexible - applied correctly - proper surface prep and thickness- is the only way to keep that great insulating, good looking roofing system performing for the entire life of the building. Our renewable warranties mean that your roof can always be under warranty, We use the best foam coatings available. conklin.com/pg.asp 
HERE'S WHAT WE DO:
1. SWEEP Remove all gravel, dirt, debris.
2. PESSURE WASH Thoroughly, all areas to be coated.
3. APPLY A heavy layer of Conklin premium coatings.
⇒ 1.9 gallons per 100 square feet.
⇒ 26 wet mils* 13 - 14 dry mils
*1 mil is .001 inch
75% - 85% Reflectivity
See More Foam Re-Coating Pictures hill-toproofing.com/gallery/v/test05'''