The short answer
Cat A is the landlord-level finish that makes an office floor usable by anyone: ceilings, raised floor, lighting, heating and cooling, and finished toilets. Cat B is the occupier's fit-out on top: partitions, meeting rooms, kitchens, finishes and furniture. Landlords usually pay for Cat A; tenants usually pay for Cat B and often have to remove it when they leave.
On this page
“Category A” and “Category B” are the terms the UK office market uses to describe how far a floor has been fitted out. Neither has a legal definition. The industry reference is the British Council for Offices’ Guide to Specification, and the line between them varies from building to building, so always read the specification rather than relying on the label.
Side by side
| Cat A | Cat B | |
|---|---|---|
| Purpose | Make the floor lettable to anyone | Make it work for one occupier |
| Typical contents | Suspended ceiling, raised floor, LED lighting, heating, cooling and fresh air to open plan, fire alarm, finished toilets | Partitions, meeting rooms, kitchen and breakout, reception, finishes, AV, furniture, services adjusted to the layout |
| Usually paid by | Landlord | Tenant (sometimes with a landlord contribution) |
| Central London guide cost | about £650 to £1,020 per m² | about £1,300 to £2,150 per m² (standard) |
| At lease end | Stays | Often stripped out back to Cat A |
Costs are converted from per ft² ranges in published Q1 2026 guides, before VAT and fees. Regional costs are typically 10 to 30% lower.
A quick test
If you are unsure which category a quote or a listing describes, ask three questions: are there any enclosed rooms on the floor apart from the core; is there a kitchen or tea point; and is there furniture? Three “no” answers usually mean Cat A.
Where shell and core fits
Before Cat A comes shell and core: the structure, facade, lifts, stairs, core toilets and main plant, with the office floors left bare. New developments are often built to shell and core, with Cat A added floor by floor as tenants are found, or all at once to market the building.
Cat A plus
Some landlords go a step further and build a kitchen, a few meeting rooms and sometimes furniture into a Cat A floor, so a smaller tenant can move in quickly without its own fit-out. It is often called Cat A plus or “fitted” space. One London contractor’s Q1 2026 guide puts it at about £95 to £140 per ft², roughly £1,020 to £1,510 per m².
What drives the cost of each
Cat A cost is mostly services: the cooling system, lighting and controls, and how much existing plant can be kept. The design density matters; the BCO’s 2023 guide recommends designing speculative offices for about 10 m² per person.
Cat B cost is mostly rooms. Every enclosed room needs partitions, a door, cooling, fresh air, lighting, sprinkler and fire alarm adjustments and often acoustic upgrades. Fewer, better-used rooms often beat many small ones.
Rules that touch both
- Fire safety: new partitions in a Cat B layout change escape routes and fire separation, so building regulations apply.
- Energy: for landlords, the minimum energy efficiency standard means a let commercial building in England and Wales currently needs an EPC of E or better unless exempt. Cat A works are the usual moment to improve the rating.
- Lease: Cat B works need the landlord’s consent, and the lease or licence usually says whether you must remove them when you leave.
Choosing between a fitted and an unfitted floor
For a tenant, taking Cat A space means a bigger upfront Cat B budget and a longer wait before moving in, but a layout designed around the business. Taking Cat A plus or a fully fitted floor means a faster, cheaper start, with less control over the layout and often a higher rent. Smaller organisations, or those unsure of future headcount, often favour fitted space; larger ones with a clear brief usually prefer to design their own Cat B.
For a landlord, the choice depends on the target market. Fitted floors can let faster to smaller tenants. Plain Cat A suits larger tenants who will strip out a landlord’s fit-out anyway, which wastes the investment.
Programme
A Cat A refurbishment of an existing floor commonly takes 8 to 16 weeks on site, driven by plant lead times. A Cat B fit-out of around 1,000 m² is typically 8 to 14 weeks on site, after 6 to 12 weeks of design, pricing and landlord consent.
How they meet at the end of a lease
Many leases require the tenant to strip out its Cat B and return the floor to Cat A condition. That cost is real and should be planned from the start; freestanding joinery and demountable partitions are easier to remove. See our dilapidations works page.
For more on each, see Cat A fit-out and Cat B fit-out, or work out a budget in the office refurbishment cost plan. Our commercial refurbishment contractors homepage sets out the other sectors.
If you are planning either, the form below sends a short brief to a contractor who covers your area.