Steve: If your spray foam installer leaves the vents open, he will be committing the 2nd of the 4 problems I described above. You will most likely have comfort and efficiency problems. You may well have condensation problems. You will be spending a lot of money on a product that likely won't perform as it should. Don't let him leave the vents open. If the installer you've chosen doesn't understand this, you may want to choose someone else. 
Solvent-based polyurethane coatings have excellent adhesion and when used as a base coat over asphalt, EPDM, TPO or PVC, it eliminates the need for a primer. The resulting savings on labor and material more than offsets the higher cost of the product. When top coated with silicone, it gives you the best of both worlds. It's also an excellent gutter and RV coating. https://www.youtube.com/v/ggLAUsiuI_o&feature=kp
Though foam insulation has a higher upfront cost than fiberglass or cellulose, it recoups this expenditure in a relatively short period of time. Additionally, the insulation’s permanence means that it will continue to generate savings over the life of your structure. The durability of this insulation means that you can rest easy in the knowledge that at least one component of your structure will stand the test of time. https://youtube.com/v/ggLAUsiuI_o

This depends on the geographic location, insulation, and cost of electricity. Lawrence Berkeley National Laboratory (LBNL), Oak Ridge National Laboratory (ORNL), National Roofing Contractors Association (NRCA), and several roofing material manufacturers have computer programs that can estimate the savings. A growing number of energy consultants are available to provide environmental regulation compliance information. http://m.youtu.be/ggLAUsiuI_o

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