That is the deciding factor.
Hot roof vs cold roof.
In cold roofs the outside air is allowed to freely flow under the roof sheathing.
Cold roof construction requires that a suitable ventilated air space exists above the insulation layer within which the air is constantly mobile being replenished by fresh incoming air whilst the air resident within the void space is being expelled via a natural vent action at another point.
Namely the insulation layers.
So what kind of difference does this make.
In hot roofs the insulation is typically installed close to the roof sheathing but the main characteristic is the space under the sheathing is closed to fresh air flow.
In climates that remain cold for a sustained period unvented roofs can cause more harm than good.
The hot roof assembly is found almost exclusively in new construction.
Basically the term cold roof refers to a traditional roof or vented roof while hot roof refers to a roof that is not ventilated and which has foam insulation attached directly to the roof sheathing.
Whether or not a hot roof is a superior setup depends heavily upon climate homeowner needs and building plans.
A little q a on the subject i tapped sean from alabama green building solutions to help clear up a few lingering questions i had about hot roofs and cool roofs.
A warm roof is much more straightforward to install and provides a superior thermal performance and is therefore more costly.
Thus your unventilated roof is indeed a hot roof.
On a flat roof this could be air in at.
In a cold roof the insulation is applied between the rafters but in a warm roof the insulation is applied on top of the existing roof surface.