[NH.Solar]

Will you be considering using metal roofing? if yes the solution is simple. Have your roofer install 2x4s 2 feet apart as the purlins and place 1.5 inch foam board in between. Tyvek or similar vapor shield would also provide an even bigger improvement but may not be a good idea on an older home because it will trap too much moisture. The purlin/foamboard solution on it's own should provide a huge improvement in both heat retention and sound control while still allowing for sufficient ventilation. Older home? talk to a seasoned local expert!