Cat A vs Cat B Fit Out: What’s the Difference?

Shell and core is the bare building: the structure, common parts and main services, with the office floors left unfinished. Cat A and Cat B are the fit-out stages that follow.

If you are taking new office space, you will hear agents, landlords and contractors talk about “Cat A” and “Cat B”. The terms describe how finished a space is, and they matter because they decide what you get from the landlord, what you pay for yourself, and how long it takes to move in. This guide explains the categories in plain English.

Shell and core

Shell and core is the building structure with its common parts: the frame, external walls, roof, lifts, stairs, reception and toilets in the core, and main building services brought to each floor. Office floors are left unfinished: often exposed concrete, no ceilings and no internal distribution of heating, cooling or lighting. Developers sometimes leave space like this so incoming tenants can design it themselves.

What does Cat A include?

Cat A turns shell and core into a usable, open-plan floor. It typically includes:

• Raised access floors for power and data.
• Suspended ceilings, or an exposed finished soffit.
• Air conditioning and ventilation distributed across the floor.
• General and emergency lighting.
• Fire detection and alarm systems.
• Basic finishes to walls, and toilets in the core.

A Cat A floor is clean and functional but empty: no meeting rooms, kitchens, desks or company identity.

What does Cat B include?

Cat B is the fit-out that makes the space work for a particular business. It typically includes:

• Partitioned offices, meeting rooms and phone booths.
• Kitchens, tea points and breakout areas.
• Floor finishes, decoration and branding.
• Changes to lighting, air conditioning and power to suit the new layout.
• IT, AV and security systems.
• Furniture, storage and reception.

Cat A+ and “plug and play”

Cat A+ sits between the two. The landlord goes beyond Cat A and adds a basic fitted layout, often meeting rooms, a kitchen, flooring and sometimes furniture and connectivity, so a tenant can move in with minimal work. It is popular with smaller occupiers and those who want to avoid managing a fit-out, at the cost of less control over design.

Side-by-side comparison

Source: Hampstead Renovations, London Office Fit-Out Cost Index Q1 2026, published 15 April 2026 (hampsteadrenovations.co.uk), checked 4 October 2026. Ranges are per sq ft of net internal area and exclude VAT; they are benchmarks, not quotes.

Who pays for what?

In a typical new letting, the landlord delivers Cat A and the tenant pays for Cat B. That split is negotiable. Landlords sometimes offer a capital contribution or rent-free period towards the tenant’s fit-out, or deliver Cat A+ space to attract occupiers. Where a tenant plans to rip out parts of the Cat A to build a Cat B layout, such as replacing ceilings, some tenants negotiate a payment from the landlord instead of works that will be wasted. Agree the details in heads of terms before you sign.

How long does each take?

Cat A is usually complete before you sign or take occupation. Cat B timing depends on size and complexity, but even a simple fit-out needs time for design, landlord approval and procurement before work starts on site. For larger floors, several months on site is common. Cat A+ can allow occupation within weeks.

What is Cat C?

You may occasionally hear “Cat C”. It is not a formal industry standard, but some contractors use it for specialist elements added on top of Cat B, such as server rooms, secure areas or high-specification AV.

Common misunderstandings

Definitions are not perfectly standardised, so one landlord’s Cat A may differ from another’s. Some include a basic tea point; some use exposed services rather than suspended ceilings. Always ask for the specification in writing rather than relying on the label, and check the condition and capacity of the services, particularly cooling and power, against the layout and headcount you plan.

Dilapidations: think about the end of the lease

Whatever you install in Cat B, your lease may require you to remove it and reinstate the space to its Cat A condition when you leave. That reinstatement cost (dilapidations) can be substantial, so factor it in when planning your fit-out and negotiating your lease.

Questions to ask your agent or landlord

• Exactly what does the Cat A specification include, and what condition are the services in?
• Is there a capital contribution or rent-free period towards our Cat B fit-out?
• Can parts of the Cat A that we won’t use be omitted in exchange for a payment?
• What are the building’s rules on working hours, deliveries and contractor approval?
• What will our reinstatement obligations be at the end of the lease?

Which should you choose?

If you want a space designed around your team and brand, a Cat A floor plus your own Cat B gives you full control. If speed and simplicity matter more, Cat A+ may suit. For an existing office, a refurbishment can achieve much of what a Cat B delivers without moving. To compare options, read our fit-out cost guide, or send us your brief and a vetted contractor will help you scope the project. See also office refurbishment in London.

Frequently asked questions

Sources

Facts and prices in this guide come from the following sources (checked 4 October 2026):

• hampsteadrenovations.co.uk (hampsteadrenovations.co.uk)

Related guides

• Office Fit Out Cost per Sq Ft in London (2026)
• How to Choose an Office Fit Out Company in London (2026)
• Cat A Fit Out in London: What’s Included and What It Costs (2026)
• Office Dilapidations in London: A Tenant’s Guide
• Office fit-out and refurbishment across London: areas we cover

This guide is general information for office occupiers, not professional cost, legal or construction advice. Costs are published benchmarks and will vary with your building, specification and programme. Always get a detailed quote and take professional advice on your lease and statutory duties.