What's the Difference Between a Cat A and Cat B Fit Out?

A Cat A space delivers the bare essentials; a clean shell with core services and basic finishes, while a Cat B fit out transforms that blank canvas into a tailor-made workspace complete with partitions, premium finishes, tech installations, and furniture.

In a Cat A fit out, you’ll typically receive the shell and core of the building plus the essential services brought to the floorplate. This usually comprises the installation of suspended ceilings, painted walls, raised floors or screed, basic lighting, heating, ventilation and air-conditioning (HVAC), fire detection and alarm systems, and mechanical risers brought to a nominated point. Cat A does not include any demountable partitioning, bespoke fixtures, or tenant-specific décor.

A Cat A+ fit out takes the Cat A specification a step further by incorporating enhanced elements such as upgraded lighting schemes, raised floor finishes, improved ceiling grids, and more comprehensive mechanical and electrical distribution to tenant zones. It provides a more complete back-of-house installation without delving into bespoke partitioning or furniture.

A Cat B fit out is the tenant’s opportunity to bring the space to life with their own brand identity and functional requirements. This phase covers the design and construction of internal walls and doors, bespoke joinery, feature ceilings, specialist lighting, full IT and telecoms cabling, kitchenette and breakout area fit-outs, and all loose furniture, artwork and accessories needed to create a fully operational workspace.

As a tenant, it’s essential to clarify with your landlord which level of finish you will be handed over – a Cat A, CAT A+ or Cat B – so that you can accurately budget, programme your project and avoid scope-creep. Each of these is discussed in more detail below.

What is Shell and Core?

Shell and core construction occurs at the very start of a building construction before any office fit out occurs (i.e. CAT A+ or CAT B) where an office space is created. The core is usually a square or rectangular reinforced concrete tube located at the centre of a building. It comprises concrete walls that have openings at each floor level for access, serving to connect various floor levels via lift shaft and stairwells.

The building shell is the basic minimum enclosure of a building, consisting of the foundation and floors at each level, the structural framework, roof coverings, exterior walls and exterior doors and windows. It also typically includes fire sprinkler systems and smoke detectors; restroom facilities for the premises located at each floor level; mechanical & electrical systems, plumbing systems, and heating, air conditioning and ventilation (HVAC) for the premises.

The concept of shell and core fit outs originated to allow tenants the flexibility to change an office layout after the developer’s notional layout of the office was completed. This would prevent money from being wasted, for instance, in taking down ceilings or lifting floors to alter the arrangement of mechanical and electrical services after the base build was completed. As a tenant of office space, it’s unlikely that you want an office left in a shell and core state. This is where a CAT A and CAT B Fit out come into play.

What is a CAT A Fit Out?

A CAT A is the basic finish of an office following the building construction – the shell and core. CAT A’s are generally commissioned by landlords who lease the building on to tenants, who in turn fit it out the office space to meet their bespoke requirements. This is not to be confused with a “Grade A” which refers to the quality of the building. CAT A (or Category A fit out) is the basic finish after the completion of the shell and core. A CAT A fit out is still essentially a blank canvas or “White Box” with an open-plan finish. This is still a relatively rough standard. It’s not suitable for tenants to move in as such.

A CAT A finish typically includes:

• Installation of basic mechanical and electrical and plumbing services
• Standard lighting installation
• Raised floors and suspended ceilings
• Heating, Ventilation and Air-conditioning (HVAC)
• Fire detection services and smoke alarms (which are essential for the health and safety of the building)
• Basic internal finishes

If you were walking around a CAT A finish you would notice a very plain-looking space with evenly spaced lighting and metal blocks of the raised floor. The raised floor is essentially a set of high-density particleboards with a steel wraparound on the top and a steel sheet at the bottom, all a uniform size of 60 x 60 cm, and laid out in a grid pattern across the entire floor. Lifting a section of these blocks would expose a space underneath (around 10-25 cm in height) which is supported by pedestals. This allows computer and electrical cables to pass under the floor to respective work stations and other areas of the office.

Note: At this point, there is no partitioning of the office space. Landlords may require at the end of the tenancy that the office space be returned to CAT A finish. This requires separate cost and timescale considerations for dilapidations.

What is CAT A+ FIT Out?

A CAT A+ sits midway between a CAT A and CAT B. It emerged as a landlord’s response to serviced office and co-working spaces (the likes of WeWork and Regus). Tenants who are less inclined to take long leases have the option of a plug-and-play office setup that comes already fitted out to a generic level, but without the bespoke design elements, fittings and choices of exactly how they want the office layed out.

CAT + Fit Outs typically include: 

• Fitted kitchens and tea points
• Partitioning for meeting rooms, breakout areas, and offices
• Furniture
• Workstations
• Re-routed Air Conditioning
• Power sockets
• IT Infrastructure

The CAT A+ model is not suitable for all companies. Many companies wish to create their own customised space to fit the company culture. If the company brand and culture are important elements to you and you want to retain a unique corporate identity, the CAT B fit out is more appropriate.

What is a CAT B Fit Out?

A CAT B fit out (also known as a Category B fit out) follows on directly from a CAT A fit out to provide completed ready-to-use office space. In contrast to the CAT A+ which provides a generic usable space (common with co-working and serviced offices), a CAT B is a space that is tailored to the requirements of a particular company brand. This is a particularly favourable option if you’re looking to take out a long-term lease and you want to separate and distinguish your branded workspace from others.

In contrast to a CAT A+, there are numerous advantages that a CAT B fit out affords its tenants:

• A unique, professionally designed office space with purpose-built areas
• A choice of functional and aesthetic interior fittings
• A more integrated design that augments your company’s brand identity
• Better utilisation of space, which comes from the ability to carefully space plan the office from a blank canvas CAT A fit out.
• Less wastage from renovating an already complete and standardised office space.
• Cost savings in not having to reconfigure ventilation ducting and mechanical and electrical systems.

As a tenant, you want a space that is designed and fitted out to motivate, energise and inspire your workforce. The design and layout of this space need to be considered alongside all sorts of practicalities, like the number of staff working at the office and working from home (see our article on hybrid office design), and the arrangement of heating, ventilation and air conditioning (HVAC) in the suspended ceiling so that it reaches each workstation. In addition, there are considerations of workplace well-being such as breakout areas and the use of plants in various parts of the office (see our article on biophilic office design). Ultimately the Cat B design and fit out should work to improve staff performance, aid retention, and generate efficiencies within a company. This, in a nutshell, is what a CAT B fit out has to offer. So where does it start, and how do you achieve it?

The CAT B starts essentially where the CAT A ends. It covers everything from interior partitioning (the creation of meeting rooms, boardrooms etc.) to the design of ceilings, walls, doors, reception areas, break-out areas, kitchens, tea points, quiet spaces, and various other essential parts of the modern office. Before a CAT B commences, a company needs to decide whether to go the traditional route, by partnering with an architect, builders, and various other parties, or to use the design and build route (D&B) where a single office fit out company is selected to look after every detail, from space planning and 3D designs to the choice of furniture, interior design, build work and final finishes. The Design and Build (D&B) model is becoming far more popular as it saves time and avoids complications where otherwise multiple independent contractors are involved.

Final Thoughts and Next Steps

While terms like Cat A, Cat A+ and Cat B are helpful for navigating fit-out requirements, there’s no universal industry standard defining exactly what each category includes. One landlord’s Cat A may differ from another’s, and your lease may require you to return the premises to its original condition at the end of your tenancy.

Our design-and-build team specialises in creating exceptional workplaces. If you need guidance or cost estimates for your office fit-out, please get in touch. With over 20 years of experience, we’re ready to advise and assist on a whole range of considerations including:

• Space planning & rationalisation – Expert in-house designers optimise your budget by making the best use of available space.
• Interior design – From initial sketches and mood boards to detailed 3D CAD models, we bring your vision to life.
• Furniture procurement – Benefit from our long-standing supplier relationships for cost savings on leading designer and ergonomic brands.
• Hybrid office design – Pioneering flexible workspace solutions to support modern working models.
• Workplace wellbeing – Thoughtfully designed breakout areas and flexible work arrangements promote employee health and happiness. See more on workplace wellbeing.
• Clean air & sustainable HVAC – In-house expertise and trusted contractor partnerships ensure efficient, eco-friendly climate control.