Hello everyone;

I am currently struggling with a question about roofs:

What is the advantage of creating a vented deck? 

If the attic space is going to be conditioned, either for living or mechanical purposes,  provision R806.3 in the International Residential Code calls for the roof deck above the space to be vented continuously from the eave to the ridge.

Even If I had a simple geometry allowing to ventilated from eave to ridge, what is the point of ventilated the deck?  And what is the advantage of doing so over creating an unvented roof with all the insulation placed on the external side?

Many Thanks in Advance.

Kind Regards
Eduardo