ISO 1 - Frame
Exterior walls, floors, or roof are mostly combustible, usually wood frame.
ISO 2 - Joisted masonry
Masonry exterior walls with combustible wood joist floors or roof.
ISO 3 - Non-combustible
Walls, floors, and roof are non-combustible, often light steel or metal.
ISO 4 - Masonry non-combustible
Masonry exterior walls with non-combustible floors and roof.
ISO 5 - Modified fire resistive
Protected structural members, usually less fire resistance than full fire resistive.
ISO 6 - Fire resistive
Reinforced concrete or protected steel with strong fire-resistance characteristics.
When unsure, select the closest match and add construction details in Property notes.