The designer should determine the type of insulation required for the construction by consideration of the factors listed below:

- Required thermal performance (‘U’ value) of the roof.

- The build-up thickness that can be accommodated at roof level.

- Imposed weight loading to the deck structure.

- Compressive strength required (the ability of the insulation to withstand loads applied directly onto the roof system surface).

- The level and type of traffic that the roof will experience both during and after construction.

- Compatibility with other roofing components.

- Required fire resistance.

- Required acoustic performance.

- Environmental properties.

Your choice - it's just a choice of one of the major systems: