Difference Between Cat A and Cat B Fit-Out
The difference between a Cat A and Cat B fit-out is the level of completion.
A Cat A fit-out creates a basic, functional commercial space. It provides the essential finishes, services and infrastructure needed to make a building ready for occupation, but not yet shaped around a specific occupier.
A Cat B fit-out takes that space further. It turns the building into a finished, working environment, with the layout, furniture, meeting rooms, branding, technology and details needed by the people who will use it every day.
Both stages matter. The right route depends on the building, the lease, the occupier, the budget, the programme and the long-term purpose of the space.
At Aptus Construction, we deliver Cat A and Cat B fit-out projects across commercial, workplace, healthcare, education and public-sector environments, managing the process from early engagement through to final handover.
What is a Cat A fit-out?
A Cat A fit-out is the stage that brings a commercial space up to a basic occupiable standard. It creates the foundation that a tenant or occupier can later adapt.
In simple terms, Cat A is the blank but usable canvas.
The exact specification can vary, but a Cat A fit-out will often include raised floors, suspended ceilings, basic wall finishes, lighting, mechanical and electrical services, heating, cooling, ventilation, fire safety systems and core infrastructure.
It does not usually include the elements that make the space specific to one organisation. There may be no meeting rooms, no furniture, no branded areas, no kitchen or breakout space, and no detailed workplace layout beyond the base provision.
For landlords, developers and asset managers, Cat A work is often about making a building lettable, flexible and ready for future use. It creates a clean and practical base that can be adapted by incoming tenants.
For occupiers, it is important to understand exactly what the Cat A specification includes before planning the next stage. A space may look ready, but it may still need significant Cat B work before people can use it properly.
What is a Cat B fit-out?
A Cat B fit-out takes a Cat A space and turns it into a finished environment designed around a specific organisation.
This is where the building starts to feel purposeful.
A Cat B fit-out may include partitioning, meeting rooms, offices, collaboration areas, breakout spaces, kitchens, reception areas, flooring, wall finishes, furniture, signage, lighting design, AV, IT infrastructure, acoustic treatments, bespoke joinery and brand-led finishes.
In a workplace, Cat B is where the space begins to reflect how people actually work. Team sizes, hybrid working, client-facing areas, focused work, informal collaboration, storage, staff welfare and future flexibility all need to be considered.
In other commercial environments, the same principle applies. A Cat B fit-out should respond to the way the building will be used day to day, not just how it looks on completion.
A good Cat B project is not simply decoration. It is the point where design, construction, services, furniture, technology and user experience are brought together into one working environment.
Cat A vs Cat B fit-out: The Main Difference
The easiest way to understand the difference is this:
Cat A prepares the space. Cat B personalises it.Cat A focuses on the base condition of the space. Cat B focuses on how that space will support the organisation using it.
Neither is automatically better. They answer different questions.
Cat A asks: “Is the space ready to be occupied and adapted?”
Cat B asks: “Does the space work for the people moving in?”
Where Does Shell and Core Fit In?
Shell and core comes before Cat A. It refers to the main structure and shared parts of the building, such as the frame, roof, external walls, windows, doors, stairs, lifts, cores and main incoming services.
At shell and core stage, the internal tenant areas are usually not finished. The building may be structurally complete, but the internal spaces still need work before they can be occupied.
Cat A builds on shell and core. Cat B builds on Cat A.
Understanding this sequence matters because it affects programme, budget and responsibility. If a space is closer to shell and core than Cat A, the amount of work needed before occupation may be greater than expected.
What is a Cat A+ fit-out?
Cat A+ sits between Cat A and Cat B. It is sometimes described as a plug-and-play fit-out because it provides a more complete workplace than a standard Cat A finish.
A Cat A+ space may include furniture, meeting rooms, kitchen facilities, workstations, breakout areas and basic technology infrastructure. It can help occupiers move in more quickly with less upfront work.
This can be useful where speed matters, or where a landlord wants to make a space more attractive to potential tenants.
The trade-off is that Cat A+ is not usually as tailored as a full Cat B fit-out. The space may function well, but it may not fully reflect the occupier’s culture, brand, working patterns or future plans.
Which fit-out Do You Need?
The right fit-out depends on what you are trying to achieve.
If you are a landlord preparing a commercial building for the market, Cat A may be the right route. It gives future occupiers a flexible base without committing too heavily to one layout or design.
If you are an occupier taking space for your own use, Cat B is usually where the real workplace planning begins. This is where decisions around teams, rooms, technology, furniture, lighting, storage, welfare and client experience are made.
If you need speed and simplicity, Cat A+ may be worth considering. It can reduce the time between lease agreement and occupation, but the specification should still be checked carefully against the needs of the organisation using the space.
The important point is not to rely on the label alone. The specification behind it matters more. One landlord’s Cat A may not be the same as another’s. One Cat B project may be a light-touch finish, while another may involve major reconfiguration, specialist joinery, MEP coordination and complex phasing.
Why Early Planning Matters
Fit-out decisions affect cost, programme, design quality, lease negotiations and long-term building performance.
Early engagement gives clients the chance to understand what the space already provides, what needs to be added, what can be retained and where risks may sit. It can also help identify whether the brief is aligned with the budget and whether the programme is realistic.
This matters because fit-out projects often involve many moving parts. Design, building services, furniture, IT, compliance, landlord approvals, procurement, access and occupation dates all need to be coordinated.
If these decisions are left too late, the project can become reactive. Costs become harder to control. Programme pressure increases. Design compromises become more likely.
A carefully planned Cat A or Cat B fit-out should feel structured from the beginning. The earlier the right team is involved, the easier it is to test the brief, manage expectations and create a space that works properly from day one.
How Aptus Delivers Cat A and Cat B Fit-Out Projects
At Aptus Construction, our fit-out work shapes internal environments from base build through to finished, ready-to-use spaces.
We manage layout, finishes, services, structure, fabric, MEP coordination and furniture where required, making sure each part of the fit-out supports the wider purpose of the building.
Our projects range from workplace refurbishment and commercial reconfiguration through to full Cat A and Cat B fit-out across live environments, public-sector buildings, healthcare facilities, education estates and commercial workplaces.
As principal contractor, we manage the process from pre-construction through to final handover. That means bringing the right people into the project early, coordinating consultants and specialist trades, managing programme and budget, maintaining clear communication, and protecting quality throughout delivery.
For clients, the value is not only in the finished space. It is in the confidence that the route to that space has been properly planned.
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A Cat A fit-out creates the base. A Cat B fit-out creates the finished environment.
For landlords, Cat A can help make a building flexible and ready for the market. For occupiers, Cat B is often the stage where the space becomes genuinely useful. For clients who need speed, Cat A+ may offer a practical middle ground.
The best fit-out projects start with a clear understanding of what the building needs to do, who it needs to support and how the work should be planned.
If you are planning a Cat A fit-out, Cat B fit-out or wider commercial refurbishment project, speak to Aptus Construction. We can help you understand the scope, shape the programme and plan the work properly from the start.