Category A fit out is the process of taking an interior space from the shell and core state and turning it into a blank canvas. By the end of the Cat A phase, all construction and essential work will be completed. The interior space will be at a stage where it can be moulded for a variety of purposes and functions, whether that be an office space, studio or conference room. Category A fit out can include the mechanical and electrical installation such as heating, aircon and lighting, raised floors, suspended ceilings, fire detection systems and toilets.

Category B fit out follows the cat a fit out stage. From the blank canvas provided by the Cat A fit out, the Cat B fit out involves creating a functional internal space tailored to the requirement of its users. During the Cat B phase, contractors such as decorators and painters will be adding decorative features that reflect the businesses branding, character and values. Category B fit out generally includes installing partitioning to create breakout rooms, meeting rooms and offices, fitting kitchen areas, floor fitting, furniture, doors and specialist lighting.