Cat A and Cat B are the two terms you'll encounter most when planning an office fit out or refurbishment, but despite how frequently they're used, there's no single industry-wide definition for either.
That inconsistency causes real confusion for tenants, landlords and property agents, and in the worst cases it leads to costly misunderstandings before a lease is even signed.
This guide covers all four stages of an office fit out in sequence, shell and core, Cat A, Cat A+ and Cat B, so you know exactly what each one means, who's responsible for it, and what it will cost you.
Cat A vs Cat B fit-outs vs Shell and Core
Office fit outs work on a sliding scale, from bare structural shell through to a fully operational, branded workplace.
There are four recognised stages, shell and core, Category A, Category A+ and Category B, and each builds on the last. Shell and core is the raw building with nothing inside.
Cat A takes it to a functional but unfinished base. Cat A+ adds a layer of usability so the space is ready for immediate occupation. Cat B takes it all the way to a bespoke, move-in-ready workplace tailored to the tenant.
Fit Out Stage | Purpose | What's Included | Responsibility | Ready for Occupation? |
Shell & Core | Structural base with no internal services | External structure, core walls, lifts, plant rooms | Developer / Landlord | No |
Category A | Prepares a space for letting, functional but unfinished | Raised floors, suspended ceilings, lighting, HVAC, fire detection, basic finishes | Landlord | No |
Category A+ | Landlord-delivered, plug-and-play space with basic usability | Cat A features plus fitted kitchen, some furniture, meeting rooms, minimal branding | Landlord | Yes (basic use) |
Category B | Fully tailored for tenant occupation and brand expression | Partitions, furniture, branded finishes, IT infrastructure, kitchen, acoustic treatments | Tenant | Yes |
Cat A fit out
What is a Cat A fit out?
A Cat A fit out is the base level of finish provided by a landlord to make a commercial office space ready for tenant customisation.
It takes a building from structural shell to a point where the core mechanical and electrical services are installed, the floors, walls and ceilings are finished to a basic standard, and the space is technically lettable, but it stops well short of being a functioning workplace.
Think of it as a blank canvas: everything a tenant needs to start their own fit out is in place, but nothing has been done to make the space usable for day-to-day work. The British Council for Offices (BCO) provides guidance on Cat A specifications, though it's worth noting there is no single mandatory standard.
Read our guide to what is a Cat A fit out, to get more insight into the Cat A fit out process.
What’s included in a Cat A fit out?
A standard Cat A fit out can include:
Raised access floors
Suspended ceilings
Mechanical and electrical (M&E) services
HVAC (heating, ventilation and air conditioning)
Lighting
Fire detection and alarm systems
Sprinkler systems
Basic wall finishes ready for decoration
Toilet and shower facilities
Lift lobbies
Building reception
The exact specification varies, since there is no single industry standard, and tenants should always confirm the precise scope with their landlord before signing heads of terms.
Learn more about our Cat A services at Area.
Who is Cat A fit out most suited to?
Cat A is almost always commissioned and paid for by the landlord, developer or institutional investor as part of preparing a space for the market.
It sets the baseline specification against which future rent reviews are assessed and against which reinstatement obligations at lease end are measured, which is exactly why understanding what your Cat A includes before you commit to a Cat B fit out matters so much.
If the Cat A scope isn't documented clearly in your lease, dilapidations disputes at the end of your term become far more complicated.
If you're a landlord planning a Cat A, it's worth reading more about landlord refurbishment and the financial impact of office refurbishments before defining your specification.
Cat B fit out
What is a Cat B fit out?
A Cat B fit out transforms a Cat A space into a fully operational, branded workplace tailored to the specific needs of the occupying business.
Unlike a Cat A fit out, which leaves the space functional and bare, a Cat B fit out incorporates a business’s identity and culture into a fully functional workplace.
Cat B is almost always enacted by the tenant, typically before they move in, and it's where the real investment in workplace design and brand expression happens.
Find out more about Cat B fit outs here.
What is included in a Cat B fit out?
A Cat B fit out typically includes:
Internal partitioning
Meeting rooms and private offices
Reception design and fit out
Bespoke flooring finishes
Wall finishes and decoration
Data cabling and IT infrastructure
Workstations and task furniture
Soft furnishings and breakout furniture
Branded graphics and signage
Kitchen and tea point facilities
Welfare and accessible facilities
Specialist lighting design
Acoustic treatments
Audiovisual (AV) equipment
Cat B scope varies significantly depending on the size of the space, the complexity of the brief and the level of finish required, a 2,000 sq ft startup office and a 20,000 sq ft headquarters are both Cat B projects, but they're entirely different in scale and ambition.
Learn more about our Cat B fit out services here.
Who pays for a Cat B Fit Out?
The Cat B fit out is the tenant's responsibility and cost. The upfront cost can be significant, but it's always worth negotiating a fit out contribution from the landlord as part of your lease, typically expressed as a sum per square foot, which can offset a meaningful portion of the build cost. Rent-free periods are a related incentive that tenants should also push for during heads of terms negotiations, and your property agent or solicitor should be helping you secure both.
One cost that's frequently overlooked at the planning stage is dilapidations liability. At the end of your lease, you'll almost certainly be required to strip out your Cat B works and reinstate the space to Cat A standard.
Factoring that cost in at the outset, and putting a schedule of conditions in place before works begin, will save you a difficult conversation later. For a fuller breakdown of what to budget, see our guide to how much an office fit out costs.
How Long Does a Cat B Fit Out Take?
For a smaller office of under 5,000 sq ft, you should allow eight to twelve weeks on site. Larger or more complex projects typically run to twelve to twenty weeks or more for the construction phase alone.
What's consistently underestimated, though, is the design phase, workplace consultancy, space planning and design development all need to happen before a contractor sets foot on site, and that can add several weeks to the overall programme.
If you're working to a relocation or lease expiry deadline, build the design phase into your timeline from day one, not as an afterthought. Our office fit out guide covers programme planning in more detail.
What is a Cat A+ Fit Out?
Cat A+ sits between Cat A and Cat B, and it's commissioned by the landlord rather than the tenant. The aim is to deliver a move-in-ready space, with furniture, a fitted kitchen, meeting rooms and the basics of a functioning office, without the bespoke branding that defines a Cat B.
Cat A + fit outs are sometimes referred to as a "plug and play" fit out for good reason, on account that a tenant can walk in and start working with minimal lead time.
Cat A+ has grown considerably in popularity since the pandemic, as landlords compete harder for tenants, and flexible, shorter lease terms have become more common.
For businesses that want speed and flexibility over full customisation, startups, businesses in growth phases, or organisations trialling hybrid working models before committing to a long-term space, it's an increasingly attractive option.
For a full breakdown, see our dedicated article on what is a Cat A+ fit out.
Shell and core fit outs
What is a shell and core fit out?
Shell and core is the stage before Cat A, it's the point at which the structural fabric of the building is complete, but no internal services or finishes have been installed. The building envelope, structural frame and core services such as centralised heating, cooling and ventilation may be in place, but the floors, ceilings and internal walls are bare. Individual floors are entirely unfinished.
Some shell and core buildings do include completed communal areas, building reception, lifts and toilets, which are sometimes delivered by the developer at this stage, but individual floor plates are left entirely raw for future tenants to develop.
One of the advantages of working at the shell and core stage is the opportunity to influence the sustainability credentials of the building from the outset. Pursuing certifications such as BREEAM or LEED at this stage, and thinking carefully about embodied carbon in the structure and materials, can make a significant difference to the long-term environmental performance of the building and its progress toward net-zero carbon targets. Find out more about shell and core fit outs here.
What’s included in a shell and core fit out?
Essentially, shell and core fit outs will include the basics a building needs to function. This includes:
The building’s fabric and structure, e.g. walls, roof, windows and floor.
Its core services, e.g. centralised mechanics and electrics (heating, cooling and ventilation)
Localised services, e.g. lighting, local heating, cooling and ventilation.
But some shell and core fit outs also include some completed communal areas, such as:
Building reception
Lifts
Toilets
What can you expect from the end result?
The end result of a shell and core fit-out provides a blank canvas for future tenants. Individual tenants or occupants can then undertake their own interior fit-out, customising the space according to their specific requirements, design preferences, and business needs. This process allows for flexibility and adaptability to different types of businesses or uses within the same building.
How can shell and core fit outs be sustainable?
The positive about working on a shell and core fit-out is that there are plenty of opportunities to make the space as sustainable as possible from the offset. This is more important than ever considering the construction sector’s greenhouse gas (GHG) emissions make up approximately 40% of global GHG emissions.
By adhering to the Leadership in Energy and Environmental Design certification (LEED) - the most widely used green building rating system in the world.
LEED for Shell and Core
LEED is a green building system that provides a set of sustainable design and construction standards for shell and core buildings. It promotes practices to ensure buildings are as environmentally friendly as possible. Gaining certification from LEED also helps to create a sustainable workplace and puts you on the right path toward net-zero carbon (NZC).
For further actionable steps to reach NZC download our free guide where you’ll find more guidance and advice.
Cat A vs Cat B fit outs: Which do you need?
The right choice depends on who you are and what you need, and it's a decision worth taking seriously before you sign anything.
If you're a landlord or developer
Cat A is still the standard market expectation for most commercial office spaces. It makes the space lettable and sets the benchmark for future rent reviews. Cat A+ is increasingly worth considering in competitive markets, in buildings where shorter or more flexible leases are being offered, or where void periods are a pressing concern, a well-executed Cat A+ can materially shorten the time to let and reduce the financial drag of an empty floor.
If you're a tenant,
The key factors to weigh up are:
Lease length: A short lease of three to five years may not justify the capital expenditure of a full Cat B fit out, particularly once you factor in the dilapidations liability at the end. In those cases, a Cat A+ space may offer better value.
Budget and timeline: Cat B projects require upfront investment and meaningful lead time. If you need to be operational quickly, Cat A+ or an inherited Cat B from a previous occupier may be a faster route.
Brand and culture: For businesses where the workplace is a genuine expression of their identity, where clients visit, where talent decisions are made, where culture is built, Cat B isn't optional. A generic space simply won't do that job.
Growth or consolidation: If your headcount is likely to change significantly during the lease term, it's worth thinking about how much of your Cat B investment is built around your current structure rather than a flexible one.
Inheriting an existing Cat B: If you're taking a space that a previous tenant has already fitted out, you'll need to assess whether to refurbish what's there or strip back to Cat A and start again. That decision depends on the quality and condition of the existing fit out, how closely it matches your brief, and what reinstatement obligations the previous tenant may have left unresolved.
Workplace consultancy is genuinely useful at this decision-making stage, before you commit to a procurement route or a lease. Find out more about workplace consultancy, office refurbishment, and the differences between traditional procurement and design and build.
Frequently Asked Questions
Does the tenant pay for a Cat B fit out?
In almost all cases, yes the Cat B fit out is the tenant's cost and responsibility. However, landlords will frequently offer a fit out contribution as part of lease negotiations, expressed as a sum per square foot, which can offset a significant portion of the build cost. It's always worth pushing for this. For current cost benchmarks, see our guide to how much an office fit out costs.
What is Cat A reinstatement?
Cat A reinstatement is the process of returning a space to Cat A standard at the end of a lease, after all Cat B fit out works have been stripped out. It's a dilapidations obligation written into most commercial leases, and the cost is often underestimated at the outset. A schedule of condition agreed before Cat B works begin is the most effective way to limit this liability.
Can you go straight from shell and core to Cat B?
Yes, it's technically possible and is sometimes done on longer leases where a tenant takes a space directly from the developer. In this scenario the tenant effectively takes on the Cat A scope as well as their own Cat B works, which requires more coordination, more upfront cost and a higher tolerance for risk. It can make sense where the tenant wants full control over the base specification from day one. Find out more about shell and core fit outs.
Is Cat A+ the same as Cat B?
No. The key distinction is who commissions and funds each stage. Cat A+ is landlord-funded and delivers a generic, usable workspace without bespoke branding. Cat B is tenant-funded and creates a fully customised workplace built around the occupying business's specific needs, culture and identity. Read more in our guide to what a Cat A+ fit out is.
How much does a Cat B fit out cost?
The market-cited range is broadly £60 to £120 per sq ft, but this varies considerably depending on specification, location and the size of the space. A highly specified London headquarters will sit at the top of that range or beyond it; a straightforward regional office fit out may come in below it. For a detailed breakdown, see our guide to how much an office fit out costs.
What is the difference between a fit out and a refurbishment?
A fit out starts from a shell or Cat A space and builds a workplace from scratch, there's nothing there yet and everything is new. A refurbishment works on an existing occupied or previously occupied space, improving or replacing what's already there. The two terms are often used interchangeably, but they describe different starting points and different scopes of work.
