If you are taking on a new commercial space in London, you will hear the terms CAT A and CAT B almost immediately. Landlords use them. Agents use them. Fit-out contractors use them constantly — often assuming you already know what they mean.
This guide explains exactly what CAT A and CAT B mean, what each one includes, what they cost, and how to plan a successful office fit-out in London without the expensive mistakes that catch most businesses off guard.
What Is a CAT A Office Fit-Out?
CAT A (Category A) is the base-level fit-out typically delivered by a landlord before a tenant moves in. It takes a shell-and-core space, bare concrete floors, exposed structure, no services, and brings it to a blank, functional standard.
A typical CAT A office fit-out includes:
- Raised access flooring
- Suspended ceiling grid with basic lighting
- Mechanical and electrical services — heating, ventilation, air conditioning
- Fire detection and sprinkler systems
- WC facilities
- Basic reception area finish
What CAT A does not include is anything that reflects how the occupying business actually works. There are no partitions, no meeting rooms, no branding, no furniture, and no design. It is a functional blank canvas, nothing more.
Some landlords also offer what is known as a CAT A+ or fitted-out spec, which adds basic furniture and a more finished appearance to attract tenants. This is not an industry standard and varies significantly between landlords.
What Is a CAT B Office Fit-Out?
CAT B (Category B) is where the space becomes a workplace. This is the fit-out that a tenant commissions, transforming a CAT A shell into a fully functioning, branded, and operational office environment.
A typical CAT B office fit-out includes:
- Space planning and interior design
- Partitioned meeting rooms, offices, and breakout areas
- Bespoke reception and front-of-house design
- Flooring upgrades, carpet, timber, luxury vinyl tile
- Feature lighting and lighting design beyond the basic CAT A grid
- Branded wall finishes, graphics, and decorative elements
- Kitchen and staff amenity areas
- IT and AV infrastructure
- Furniture, workstations, and storage
- Bespoke joinery, reception counters, storage walls, feature elements
CAT B is where design decisions directly affect how your team works, how clients perceive your business, and how efficiently the space operates day to day. It requires a proper brief, a design process, and a coordinated delivery programme.
For a full breakdown of what goes into planning a successful workplace, our guide to commercial office design in London covers how layout decisions affect productivity and long-term commercial performance.
CAT A vs CAT B: What Is the Practical Difference?
The simplest way to understand the distinction is this.
CAT A is what you inherit. CAT B is what you build.
A business taking on a CAT A space needs to commission a full CAT B fit-out before anyone can actually work there. A business taking on a pre-fitted CAT A+ space may need only a partial CAT B programme, furniture, branding, IT, to become operational.
Understanding which starting point you are working from is one of the first questions a specialist office interior designer will ask, because it directly determines the scope, budget, and programme of the fit-out required.
CAT A Fit-Out Cost in London
CAT A fit-out costs in London are typically borne by the landlord, but understanding them matters when negotiating a lease. Landlord-funded CAT A works in London typically cost between £35 and £80 per square foot depending on the quality of the building and the extent of M&E services installed.
When a tenant is responsible for CAT A works — in older buildings or shell-and-core agreements — budget between £40 and £75 per square foot for a standard commercial specification in London.
CAT B Office Fit-Out Cost Per Square Metre in London
This is the figure most businesses want to know — and it varies more than most people expect.
As a realistic guide for London in 2026:
- Basic CAT B fit-out: £60 to £90 per square foot (approximately £650 to £970 per square metre)
- Mid-range CAT B fit-out: £90 to £130 per square foot (approximately £970 to £1,400 per square metre)
- High-specification CAT B fit-out: £130 to £200+ per square foot (approximately £1,400 to £2,150+ per square metre)
For a typical 2,000 square foot (186 square metre) London office, a mid-range CAT B programme will cost in the region of £180,000 to £260,000 before furniture, IT, and professional fees.
For a detailed breakdown of what drives these figures and how to budget accurately before going to tender, our full guide to office fit-out costs in London covers every cost category with realistic numbers.
What Drives CAT B Office Fit-Out Costs Up?
Several variables move the cost of a commercial office fit-out significantly in either direction.
Partitioning. Glass-fronted meeting rooms and acoustic partitioned offices add cost quickly. Full-height acoustic glass can cost £600 to £1,200 per linear metre for quality commercial specification.
Reception and front-of-house. The reception is the highest-specification area in most offices. Bespoke joinery, feature lighting, branded graphics, and quality flooring concentrated in one zone drive the cost per square metre in this area well above the office average.
Breakout and amenity areas. Kitchen fit-outs, café-style breakout zones, and wellness spaces require specialist contractor input and contribute disproportionately to total project cost relative to their floor area.
M&E modifications. Any changes to the mechanical and electrical infrastructure inherited from the CAT A — moving air conditioning units, upgrading electrical capacity, adding data points — are costed separately and can add significantly to the programme budget.
Furniture. Furniture is often treated as a separate budget line but should be planned as part of the CAT B design process from the outset. Mismatches between the designed space and the furniture specification are one of the most common and most avoidable sources of post-completion disappointment.
How Long Does a CAT B Office Fit-Out Take?
Timeline is as important as cost for most London businesses, particularly those paying rent on a new space while fit-out works are underway.
As a realistic guide:
- Small office (under 2,000 sq ft): 6 to 10 weeks on site
- Medium office (2,000 to 5,000 sq ft): 10 to 16 weeks on site
- Large office (5,000 sq ft+): 16 to 24 weeks on site
These are construction timelines only. The design and planning phase — space planning, concept design, technical drawings, procurement, and contractor tender — typically adds a further 8 to 14 weeks before site work begins. A business targeting an office opening date should be engaging a design team at least five to six months in advance of that date for a mid-size project.
For smaller office projects where the priority is maximising efficiency within a compact footprint, our guide to small office design in London covers how smart planning can deliver a high-quality result without an oversized budget.
Common CAT B Fit-Out Mistakes London Businesses Make
Appointing the contractor before the design is complete. Going to tender with incomplete drawings means contractors cannot price accurately, and scope additions during the build programme are priced at a premium. Complete the design first.
Separating design and project management. When the design team and the fit-out contractor are working from different sets of information, the gap between design intent and built result widens. A coordinated approach, where the designer is involved through delivery, produces a consistently better outcome.
Underestimating the furniture budget. Furniture is frequently the last thing budgeted and the first thing cut. In a well-designed office, furniture is not a finishing touch — it is a core component of the spatial design. Budget for it properly from the start.
Ignoring acoustics. Open-plan offices that have not addressed acoustic performance become operationally difficult within weeks of opening. Acoustic ceiling treatments, partitioned focus areas, and considered material choices should be built into the CAT B specification from day one.
If you are planning a commercial office fit-out in London and want to discuss your project with a specialist team, our work across open-plan office design and full CAT B delivery demonstrates exactly how we approach the balance between design quality and operational performance.
Planning Your CAT B Fit-Out: Where to Start
The best outcomes in office fit-out come from starting the right conversations early. Before any designer or contractor is appointed, the business needs clarity on three things: the operational brief (how the team works and what the office needs to support), the realistic budget (including contingency), and the critical timeline milestones.
With those three elements in place, a specialist team can design and deliver a workplace that performs commercially from day one, rather than a space that looks impressive in photographs but creates operational friction every day it is in use.
If you are planning a CAT A or CAT B office fit-out in London and want to discuss your project, book a free consultation with Oraanj Interiors and we will help you plan a workplace that works as well as it looks.
