Cat A vs Cat B fit-out: what the IT specification should include at each stage

What Cat A and Cat B actually mean

Cat A is the landlord's contribution: the building is handed over in a functional but blank state. Services are connected, the shell is complete, raised floors and ceiling grids are in – but there's no occupier-specific fit-out. The space is ready for a tenant to take possession and begin their own works. It's a building waiting to be used, not one ready to work in.

Cat B is the occupier's fit-out: the space is partitioned, furnished and configured for a specific tenant's use. Meeting rooms, kitchen areas, branded reception, AV systems – all of this sits in Cat B. The occupier either commissions and pays for Cat B directly, or negotiates a contribution from the landlord as part of the lease deal.

There's also Cat A+ (sometimes called enhanced Cat A), which has grown in relevance as flexible and build-to-let commercial property has become more common. In a Cat A+ specification, the landlord goes further – installing active Wi-Fi, furnishing open-plan areas and fitting out meeting rooms to a basic standard. The intent is a plug-and-play office that a tenant can occupy without any additional fit-out spend. The IT infrastructure is selected and locked by the landlord; tenants take it or negotiate modifications at their cost.

IT infrastructure in Cat A: what the landlord provides

The Cat A IT scope is passive infrastructure – the framework that makes Cat B possible, not the working network itself. It should include:

• Telecommunications ducts and risers: incoming duct routes from the street to the building's comms room, and vertical risers between floors. These need to be sized adequately for the building's anticipated occupancy and should accommodate multiple carriers.
• Comms room fit-out: a properly specified comms room – or floor-by-floor IDFs on larger buildings – with appropriate floor area, a dedicated power supply (including emergency power), adequate cooling, earthing and physical containment for cable entry. This is where Cat B cabling will terminate, so the room needs to be large enough to accommodate what Cat B will bring.
• Structured cabling to floor plates: horizontal cable containment – trunking, cable trays and conduit – run from the comms room to each floor zone. Some Cat A specifications stop at containment only; others include cables terminated in the comms room but not to individual outlets. The scope should be explicit, not assumed.
• Building-wide systems: CCTV, access control, fire alarm integration and building management system (BMS) connectivity are typically Cat A – the landlord owns and operates these systems throughout the tenancy.
• Power and containment capacity: sufficient electrical capacity and physical containment routes to support the Cat B works the tenant will carry out. This means the M&E and IT designs need to be coordinated at RIBA Stage 3, before the Cat A contractor mobilises.

What Cat A does not typically include: active network equipment (switches, wireless access points, routers), horizontal cabling to individual desks or meeting rooms, or any occupier-facing technology. Those sit firmly in Cat B.

IT infrastructure in Cat B: what the occupier specifies

Cat B is where the network becomes functional. The occupier – usually working with an IT consultant or their technology team – specifies and installs:

• Horizontal cabling from the comms room to every desk position, meeting room, access point location and device drop
• Wi-Fi access points, wireless controller and network management platform
• Active switching infrastructure – core switch, access switches, patch panels – installed in the Cat A comms room
• AV systems for meeting rooms: screens, conferencing hardware, room booking panels
• Telephony infrastructure, whether VoIP handsets or soft-phone systems
• Additional power and data points beyond the base Cat A provision
• Specialist systems specific to the occupier's use – trading floor infrastructure, medical equipment networks, high-density compute environments

The occupier's Cat B IT contractor works within the physical infrastructure the landlord has provided. If that infrastructure is inadequate – wrong cable category, insufficient comms room space, containment not routed where it's needed – Cat B becomes significantly more expensive and the programme slips.

Where disputes arise

The boundary between Cat A and Cat B IT is where most problems originate. The common flashpoints:

Cable category mismatch. The landlord installs Cat 6 structured cabling as part of Cat A – which was the market standard when the project was designed. The incoming tenant needs Cat 6A for 10 Gigabit Ethernet. The existing cabling doesn't support it. Who pays to re-cable? The answer usually ends up in the heads of terms negotiation, but it's a dispute that could have been avoided with an explicit Cat A IT specification agreed before planning.

Comms room too small. The Cat A comms room accommodates the building-wide systems – CCTV NVR, access control server, BMS gateway – and leaves barely enough space for a single rack. When the tenant's Cat B IT contractor arrives, there's nowhere to install the switching infrastructure. Floor space in comms rooms costs almost nothing at design stage; it costs a great deal to create retrospectively.

Containment not where it's needed. Cat A containment was designed around a speculative floor plan. The tenant's actual layout puts high-density workstations in a zone where there's no containment route. Running new trunking after the ceiling is finished – through completed partitions and finished surfaces – is expensive and disruptive.

Incompatible building-wide systems. The landlord's CCTV uses a proprietary NVR platform that can't be integrated with the tenant's security management system. The tenant wanted unified visibility; what they've got is two parallel systems that don't talk to each other. Open-protocol specifications at Cat A stage prevent this.

Writing a good Cat A IT specification

A Cat A IT specification that actually protects the developer, the agent and the incoming tenant covers the following:

• Cable category: Cat 6A as the minimum for any new structured cabling installation in 2026. Specify the manufacturer and require FLUKE certification for every run.
• Comms room dimensions and power: floor area, clear working height, power supply rating (include UPS provision), cooling capacity and earthing arrangement. These need to be sized for what Cat B will install, not just for what Cat A requires.
• Outlet density per zone: where Cat A includes cabling to floor plates, the specification should define a minimum outlet count per square metre or per workstation density assumption.
• Containment routing plan: cable tray and trunking routes shown on coordinated drawings, confirmed against the M&E and structural services to avoid conflicts.
• Building-wide system protocols: specify open-protocol systems for CCTV, access control and BMS where possible, to preserve the tenant's ability to integrate with their own management infrastructure.

All of this should be agreed between the design team, M&E contractor and an independent IT consultant at RIBA Stage 3. By Stage 4, the opportunity to avoid the most expensive mistakes has largely passed.

What incoming tenants should check before signing a lease

If you're taking occupation of a Cat A space, the IT specification is part of your due diligence – as important as the mechanical services schedule or the floor loading data. Before heads of terms are agreed, request:

• The Cat A IT specification document – not a summary, the full spec
• Confirmation of cable category and FLUKE test certification
• Comms room drawings showing available floor area and power capacity
• Containment routing drawings, to check coverage matches your intended layout
• Details of building-wide systems – CCTV, access control – and whether they're open protocol or vendor-locked

If the landlord can't provide these documents, or if the specification doesn't meet current standards, that's a negotiating point before you sign – not a problem to solve after practical completion.