Spray on systems are becoming much more widely accepted now a days. They vary in the materials used and the length of the warranty. I know they can come in much cheaper compared to the cost of total roof replacement and usually cheaper than new roof overlays. Obviously you must do your homework and decide which is best for your situation. I would compare total lifetime costs and think about any added benefits such as reduced energy usage through reduced cooling costs or renewable warranties and reduced maintenance costs. I am not going to recommend any one product since my opinion may be biased since I do work for
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, Insulating Coatings Corporation. I think if you do the research and read the articles from the major roofing magazines and then get references and literature and then do a full cost comparison, you will see that spray on systems can be a very effective and economical choice.