An office fit out will secure the progression and growth of your company for the years to come, so it’s imperative to get it right.

To understand the difference between a CAT A and CAT B fit out it’s helpful to peel back the layers and to look at the various types of fit out agreements between landlords and tenants: CAT A, CAT A+ and CAT B. These are discussed in more detail below.

What is a Fit Out?

A fit out is the full end-to-end process of creating a space that is ready for occupation. This includes everything from the installation of facilities like bathrooms, to raised floors, and the creation of meeting rooms, breakout areas and kitchens.

As the tenants of an office building, it’s important that you confirm with your developer or landlord regarding the finish required. Depending on the agreement between the tenant and the landlord, an office building can be fitted out to CAT A, CAT A+ or Cat B standard, where the building is fully complete and ready to move in. Each of these are discussed in more detail below. 

What is Core and Shell?

At the very start of the spectrum, before any fit out occurs, is a core and shell construction. 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 an 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 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.

CAT A Fit Out
Example of a CAT A Fit Out

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 teapoints
  • 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?

Platinum Equity CAT B Office Fit Out - Mayfair, London
Platinum Equity CAT B Office Fit Out – Mayfair, London


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 which 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 wellbeing 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.

Concluding Thoughts and Next Steps

While terms such as CAT A, CAT A+ and CAT B are useful in navigating fit out requirements, the fit out industry doesn’t have a universal standard on what each category of fit out means, or what’s included as part of the agreement. One landlord’s understanding of CAT A may differ from another. Additionally, depending on your lease agreement, you may be required to return the premises to its original state when your tenancy ends. 

Our design and build team specialise in helping tenants find, build and design exceptional workplaces. If you require help and advice on any of the fit out stages, including dilapidation, feel free to contact us to discuss things in more detail. With over 18 years of experience in the fit out industry  our team are ready to advise and assist you with any of the following:

  • Space planning and rationalisationwe have an in-house team of designers who specialise in office space planning and provide exceptional recommendations that help make the best utilisation of space within your budget.
  • Interior design – from sketches and mood boards to the provision of 3D CAD designs, our team of office designers are second to none in bringing exciting ideas to life. 
  • Furniture – our longstanding relationships with leading suppliers allows us to offer you significant cost savings in purchasing office furniture from a wide range of leading brands including designer and ergonomic office furniture (see our section on furniture suppliers)
  • Hybrid office design – with years of experience in enabling flexible workspaces for clients, we are now leading the way in hybrid office design.
  • Wellbeing in the workplace – our team is skilled in the creation of workplaces that encourage workplace wellbeing, with the inclusion of breakout areas and flexible work arrangements.
  • Clean air and sustainable HVAC solutions – we offer expert in-house advice on the installation of HVAC and have long standing relationships with HVAC contractors.


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