What’s the difference between
Cat A and Cat B fit-outs?

Category A (Cat A) fit-outs provide a functional but unfurnished office shell, typically delivered by the landlord. Category B (Cat B) fit-outs — also known as tenant fit-outs — are the internal works an occupier carries out to make the space ready for daily use. Cat A includes basic finishes and services; Cat B completes the space with partitions, furniture, IT, and branding.

If you're reviewing a lease or looking at office plans, you've probably come across the terms "Cat A" and "Cat B" fit-out. These are industry-standard classifications, not legal requirements, used across the UK to describe the level of finish an office space has when handed over. This post breaks down what each category means, what's included, and how they differ — using definitions from RICS, BSRIA, and common industry practice.

Types of Office Fit-Out

Office spaces in the UK are usually delivered in one of four formats:

• Shell and Core: Just the building's structure — frame, façade, lifts, and lobbies. No internal services, lighting, or flooring.
• Cat A Fit-Out: A blank, functional shell with mechanical and electrical systems, lighting, basic flooring, and ceilings.
• Cat A+ Fit-Out: A landlord-delivered package that includes some Cat B elements, like fitted kitchens or meeting pods, to make the space more usable.
• Cat B Fit-Out: The occupier's works that complete the space with layout, furniture, and branding.

Category A (Cat A) Fit-Out

A Cat A fit-out is typically completed by the landlord to make the space legally lettable. It includes building services and finishes but leaves layout, furniture, and branding to the occupier. According to RICS and BSRIA, Cat A is the base level required for occupancy. It's intended as a clean slate for the tenant to customise.

Category B (Cat B) Fit-Out

A Cat B fit-out is completed by the occupier to turn the blank Cat A space into a workplace tailored to the team's needs. It includes everything needed to support functionality, brand identity, and workplace wellbeing. These works are tailored to the occupier's specific needs and complete the interior design of the workspace. RICS defines Cat B as the final layer of works installed within the demised area.

Cat A+ and Plug-and-Play Fit-Outs

Cat A+ is an informal term used for spaces that go beyond standard Cat A. Landlords may include meeting rooms, fitted kitchens, and basic furniture to attract tenants looking for ready-to-use space. This model is common in flexible office arrangements and short-term leases. Some landlords now offer enhanced Cat A fit-outs with select Cat B elements already installed.

Fit-Out Timeline and Responsibilities

The typical fit-out process follows this sequence:

1. Shell and Core — Delivered by the developer
2. Cat A Fit-Out — Installed by the landlord
3. Cat A+ — Optional landlord-led enhancement of Cat A
4. Cat B Fit-Out — Installed by or for the occupier

In most leases, landlords deliver Cat A or Cat A+ by handover, while tenants handle the Cat B fit-out. Tenants are often required to return the space to Cat A condition at lease end, which affects dilapidation costs.

Lease Implications and Permissions

In most commercial leases, the landlord delivers the space in Cat A condition. The tenant then carries out the Cat B fit-out to suit their operational needs. Where the space is already fitted out from a previous occupier, tenants often choose an office refurbishment instead — adapting what's there rather than stripping back to Cat A. It's also common for the lease to include a clause requiring the tenant to return the space to Cat A at the end of the term.

This return condition — often tied to dilapidations — can add cost, especially if the Cat B fit-out involved heavy customisation. It's worth reviewing these terms before starting work, as some landlords may allow elements of the fit-out to remain in place or agree a financial settlement instead.

Before any Cat B works begin, tenants typically need to submit plans for landlord approval. This ensures that any changes won't interfere with building systems or common areas, and that reinstatement obligations are clear from the start.

Market Trends

There's a growing focus on sustainability in office fit-outs. Landlords are increasingly criticised for delivering full Cat A fits that tenants later strip out. Industry leaders now recommend fitting out one floor as a sample or using VR to visualise Cat B options. Meanwhile, tenants continue to demand flexible layouts, good air quality, and pre-installed IT — pushing demand for Cat A+ and hybrid fit-outs.