The Difference Between Cat A and Cat B Fit Out

An office fit out can be a transformative project for your business. Transforming your workplace is undeniably a big task, but you’ll be reaping the rewards for years to come. There are a number of words and phrases associated with the fit out process that you might not be familiar with, but that are crucial to understand if you’re planning a relocation and weighing up your options. Here, we explain the primary four types of office fit out, as well as the key differences between the two most common types: Cat A and Cat B.

What is an office fit out?

Put simply, a fit out is the process by which an office space is developed, with a view towards fulfilling the needs and requirements of those using it. It’s a reshaping and reconstruction of a space to align its functionality with what the occupants need it to do.

There are four main types of fit out. These are: shell and core, Cat A, Cat B, and Tenant-Ready.

These terms are somewhat flexible, and there are no standard industry definitions for the different fit out types. However, there are several key features that define each type.

Shell and Core

Shell and core, also known as ‘base build’, is the absolute barebones fit out that covers only the outer framework of the building, the inner core, and the concrete and metal frame of the space. Lift shafts are also included.

At this stage, there is no interior installation. Even the most basic services – lighting, air conditioning, etcetera – aren’t present in a shell and core.

The Differences Between Cat A and Cat B

Cat A and B fit outs are very common, and are clearly distinguishable.

Cat A fit out is a basic fit out one step above shell and core, where the space is operational but empty, ready to be moved into.

Cat B fit out is the further process of bringing in the workplace elements, building the space into a fully functioning office.

Let’s take a look at both types in a little more detail.

Cat A  

This is also referred to as the ‘landlord fit out’, because landlords often commission Cat A fit outs, rendering the office space into a blank canvas that can be put on the market.

It’s the first fit after shell and core, leaving the interior of the building empty. This allows the occupier to establish and contract out their own design and construction.

Cat A includes the installation of electrical (including lights), plumbing and mechanical services, as well as fire detection systems, suspended ceilings and raised access flooring.


Cat B

In contrast to Cat A, this is the ‘tenant’s fit out’, usually carried out by a new tenant of an office space, before they move in, in conjunction with a design & build company.

This fit out incorporates everything that makes an office space functional, but, most importantly, it provides the framework to bring the tenant’s company to life.

From an empty shell, a fully functional, vibrant office is created; an exciting hub for the tenant’s business.

A design & build partner joins you in the design phase and builds your space: everything from specialist facilities (teapoints, meeting rooms, collaborative zones) to the installation of technical equipment, furniture, and biophilic elements.

For more information on Cat B fit outs, check out our guide.



The final type of fit out is the Tenant-Ready fit – also known as Cat A+. This form of fit out is commissioned by landlords looking to enter the burgeoning ‘flexible working’ market.

The Tenant-Ready fit out is essentially a fully functioning office space, replete with all standard office amenities – meeting rooms, breakout spaces, workstations, kitchens, IT infrastructure, power, etcetera – that a tenant can quickly move into and begin working immediately.

This is particularly attractive for smaller companies looking to begin operating in a space without worrying about the complexities that a Cat B fit out would bring.

For more information on Tenant-Ready spaces, check out our guide.


Your next fit out starts here

If you’re just at the outset of deciding on the next steps for your business in terms of potential relocation or renovation, or even just assessing the current and future needs of your workplace, we’re here to help.

As the UK’s leading, award-winning design and build firm, we have thirty years of experience delivering extraordinary office spaces.

Get in touch with us here.