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I am planning on reroofing and redoing the insulation in my home in the Central Valley of California. The spray foam insulation salesman says they would seal up the attic and enclose the attic space with insulation so that it will be the same tempurature as the interior of the house. He also says the foam will block moisture so you don't need ventilation to remove moisture to prevent rot in the roof. The roofer says sealing off the vents will void the roof warrenty. The foam insulator responds that the roofer doesn't know his technology. Where is the source that can be trusted to resolve this? The spray foam insulation seems better than fiberglass in other respects so if this could be resolved I'd go with spray foam.

 To answer your question, " Where is the source that can be trusted to resolve this?"  There isn't one. Which salesman do you want to believe? 

The roofer is going on the manufactures guide lines and your foam guy is going on a kinda out there principle of building science.

Think about this!  "The spray foam insulation salesman says they would seal up the attic and enclose the attic space with insulation so that it will be the same tempurature as the interior of the house.". 

Do you live in your attic?  If not, why should you expend resources/money on heating/cooling it?

There are better ways to effectively and economically improve the comfort and safety of a home.