Unvented roof design involves apply insulation directly to the underside of the roof service, closing off all outside venting to the attic/roof space, and creating a conditioned attic space. This type of design is  energy efficient and will not harm roofing materials such as shingles. Building Science Corpration is a consulting/engineering firm that works closely with both the U.S. Department of Energy's Build America program and various building code bodies. They produce a series of technical building science and building phsyics articles. The one listed below is on various roof designs and includes unveted roof construction.

Roof Design - Building Science Corproation article on various roof designs, included unvented roof construction.