Cat A is the landlord's base fit-out that brings a shell-and-core building to an open-plan, lettable standard; Cat B is the tenant's fit-out that turns that blank space into a finished, branded workplace. This guide explains what each category typically includes, who usually pays for what, and where Cat A+ and dilapidations fit in.
Commercial fit-out is usually described as a sequence of stages, and it starts with shell and core. This is the building as the developer hands it over: the structure, external envelope, common parts, lifts and main plant are complete, but the office floors themselves are bare concrete with capped-off services. Reception areas, lift lobbies and toilets in the common parts are typically finished; the lettable floorplates are not.
Everything that follows — Cat A, then Cat B — builds on this baseline. Understanding where shell and core ends is the easiest way to understand where Cat A begins.
Cat A is the landlord's fit-out. It takes a shell-and-core floor to a functional, open-plan condition that can be marketed to tenants — sometimes described as 'lettable condition'. The space is finished but deliberately generic: no partitions, no furniture, no branding.
A typical Cat A specification includes raised access floors, suspended ceilings, basic mechanical and electrical services distributed to suit an open plan — lighting, heating, cooling and ventilation, power to floor boxes or perimeter — plus fire detection, life-safety systems and basic internal finishes to walls and columns.
The scope is not fixed by any statute or single standard; it is defined in the building's specification and lease documents, and it varies between landlords. But the principle holds: Cat A gets the floor to a consistent, serviceable open-plan baseline that any incoming tenant can then adapt.
Cat B is the tenant's fit-out. It transforms the open Cat A floor into a working environment designed around a specific occupier: partitions and glazed screens forming offices and meeting rooms, joinery, tea points and kitchens, floor finishes, decoration and branding, furniture, and IT and audio-visual infrastructure.
Cat B also has a significant M&E component, and this is where many projects go wrong. Dividing an open floor into cellular rooms changes how air, heating, cooling, lighting and fire detection need to work. Ductwork is re-routed, lighting is re-circuited and controls re-zoned, and small power and data are distributed to desks and rooms. The Cat A services were designed for open plan; Cat B adapts them to the actual layout.
Because Cat B alters base-building systems, landlord consent — usually through a licence for alterations — is normally required before work starts.
As a general rule of UK practice, the landlord funds shell and core and Cat A, because these create the lettable asset. The tenant funds Cat B, because it is specific to their occupation.
In reality the line is negotiated. Landlords often offer incentives — rent-free periods or a capital contribution towards the tenant's fit-out — and some tenants take space before Cat A is complete and agree a hybrid arrangement. In a plug-and-play or managed offer, the landlord may fund fit-out beyond Cat A and recover the cost through rent.
The commercial split is set out in the heads of terms and the lease, so it varies deal by deal. Treat the landlord-pays-Cat-A, tenant-pays-Cat-B pattern as the typical starting point rather than a rule, and take advice on the specifics — this is general guidance, not legal advice.
Cat A+ (sometimes called 'plug and play') sits between the two categories. The landlord fits the space out beyond Cat A — typically with a simple layout of meeting rooms, a kitchen or tea point, finishes and sometimes furniture — so a smaller occupier can move in with minimal work. It has become common for suites aimed at tenants who want speed and certainty over a bespoke design.
Dilapidations sit at the other end of the lease. Most leases oblige the tenant to reinstate the premises at expiry — commonly stripping out the Cat B works and returning the floor to something close to its Cat A condition, depending on the lease wording and any licence for alterations. A sensible occupier prices this future liability into the fit-out decision at the start, not the end, of the term.
Because reinstatement obligations turn on the exact drafting of the lease, this is another area where professional advice matters.
The most common friction in fit-out projects is the junction between the architectural works and the building services. Partitions that cut across air-distribution paths, lighting that no longer matches the room layout, fire detection and emergency lighting that need re-designing for cellular spaces — all of it is M&E work triggered by Cat B decisions.
A contractor that delivers mechanical, electrical and public health engineering alongside the fit-out can co-ordinate these interfaces from day one: services designed to the layout rather than patched around it, one programme, one point of responsibility, and commissioning that covers the floor as a whole. Standards such as BS 7671 for electrical work and CIBSE guidance for building services set the method.
AMPM delivers Cat A and Cat B fit-out with in-house MEPH engineering across London and the South East, which keeps the design of the space and the design of its services in the same conversation.
It depends on the specification, but for the occupier the relevant cost is usually Cat B, since the landlord typically funds Cat A. Cat B costs vary widely with the density of partitions, the quality of finishes and joinery, and how much the M&E services need to be adapted to the layout. A simple open-plan Cat B is at the lower end; a heavily cellularised space with high-spec finishes and extensive services alterations is at the upper end.
Technically the space is functional — it has floors, ceilings, lighting and climate control — but it has no partitions, furniture, kitchens or IT infrastructure, so in practice almost no occupier moves into pure Cat A. Tenants either commission a Cat B fit-out or take a Cat A+ (plug-and-play) suite where the landlord has already added a basic layout and finishes.
Almost always. Cat B works alter the premises and usually connect into base-building systems, so most leases require the landlord's consent through a licence for alterations before work begins. The licence records what is being installed and typically shapes the reinstatement (dilapidations) obligations at the end of the lease, so it is worth getting the documentation right at the outset.