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In today’s commercial property market, it’s important for property owners, tenants, and contractors to understand the difference between CAT A and CAT B fit-outs. Whether you’re developing office space or industrial warehouses, these different levels of fit-out serve a purpose and require consideration of many technical and practical elements.
The Key Differences Between CAT A and CAT B Fit-outs
Understanding the main differences between CAT A and CAT B fit-outs is key for property owners, developers and tenants. Both are important stages of commercial property development but serve different purposes and levels of customisation.
CAT A Fit-outs: The Base Build
CAT A fit-outs are the basic, landlord grade finish of a commercial space. These include:
Basic electrical infrastructure and distribution
Standard suspended ceilings and raised floors
Essential mechanical and electrical services
Primary air conditioning systems
Basic fire detection and prevention systems
Minimal internal walls (mainly core walls)
Standard lighting arrays
Base level floor finishes
CAT B Fit-outs: The Tenant’s Space
CAT B fit-outs turn the base build into a fully functional, branded space. These customisations include:
Custom internal walls and partitions
Specific room layouts and floor plans
Bespoke lighting designs
Enhanced electrical and data infrastructure
Meeting rooms and collaborative spaces
Kitchen and break-out areas
Brand specific finishes and decoration
Furniture, fixtures and equipment (FF&E)
Key differences
The main differences can be summarised as:
Purpose: CAT A is a blank canvas, CAT B is a finished space
Timing: CAT A post construction, CAT B is often post tenant acquisition
Responsibility: CAT A landlord funded, CAT B can be tenant funded
Customisation: CAT A standardised, CAT B highly customised
Duration: CAT A takes longer due to base build work; CAT B can be quicker but varies with complexity
Cost
You need to understand the costs for each:
CAT A costs are included in the building’s core development budget
CAT B costs vary greatly depending on tenant requirements and specifications
Some costs can be shared through landlord contributions or tenant improvement allowances
Future proofing should be considered in both stages to avoid long term costs

CAT A Fit-outs
A CAT A fit-out is the basic level of finish that landlords provide to make a space functional and compliant with building regulations. This first stage creates a blank canvas for future tenants and ensures all the fundamentals are in place.
Office CAT A Specifications
In office environments, CAT A installations include essential building services and infrastructure. The scope consists of suspended ceilings, raised access flooring and the fundamental mechanical and electrical services.
The electrical infrastructure at this stage is primary distribution, with main distribution boards, essential lighting systems, and fire detection equipment. Basic lighting is uniform LED panels or downlights in a standard grid pattern with emergency lighting to current regulations. Air conditioning and ventilation systems are installed but may require final commissioning based on the final office layout.
Warehouse CAT A Specifications
Warehouse CAT A fit-outs are very different from office specifications due to their industrial nature. These installations focus on robust, industrial grade systems that can support heavy industrial use. High bay lighting is standard, usually energy efficient LED solutions that provide sufficient lighting for large open spaces.
Three phase power distribution is the backbone of the electrical infrastructure with capacity planning for various industrial applications. Loading-bay areas get special attention with standard electrical provisions for dock levellers and security systems. Fire safety systems are more comprehensive as there are more risk factors in industrial environments.

CAT B Fit-outs in Detail
CAT B fit-outs turn the CAT A space into a fully functional, bespoke environment that meets the operational requirements.
Office CAT B Elements
Office CAT B works to create the final working environment:
- Bespoke lighting designs for different work zones
- Power to workstations and specialist areas
- Complete data and comms infrastructure
- Access control and security systems
- Audio visual installations for meeting rooms
- Specialist areas such as server rooms and comms hubs
At this stage, the electrical installation becomes more complex, with power requirements for different areas. Meeting rooms need sophisticated lighting control systems, and open-plan areas need flexible power solutions to accommodate changing layouts.
Warehouse CAT B Elements
Warehouse CAT B fit-outs are about operational efficiency and business-specific requirements. Key elements:
- Electrical infrastructure for racking systems
- Installation of charging stations for MHE
- Power for specialist machinery
- Office mezzanine installations with services
- Temperature-controlled zone requirements
- Enhanced security systems, including CCTV and access control

Technical Considerations
Office-Specific Requirements
Office environments require:
- Power load calculations based on occupancy and equipment
- Lighting control systems for energy efficiency
- Small power distribution through raised floors or dado trunking
- UPS for critical equipment
- Emergency lighting to BS 5266-1
Warehouse-Specific Requirements
Warehouses have specific technical challenges:
- Heavy machinery power with isolation
- Industrial lighting that minimises shadows and dark spots
- Three phase power for equipment
- Charging infrastructure for electric forklifts and MHE
- Emergency power for critical operations
Energy Efficiency and Sustainability
Modern fit outs must be energy efficient and sustainable. This includes:
- LED lighting with intelligent control systems
- Motion sensors and daylight harvesting
- Energy monitoring and building management systems
- VSD for motors and pumps
- Smart metering for power consumption analysis
Common Challenges and Solutions
Office Challenges
Office fit-outs have:
- Working in occupied spaces requires planning
- After hours of working to minimise disruption
- Integration with existing services
- Dust and noise control during installation
- Business continuity
Solutions will typically involve:
- Detailed project phasing
- Temporary power
- Coordination with other trades
- Stakeholder communication
- Health and safety measures
Choosing a Contractor
Choosing the right electrical contractor is vital to a successful fit out. Consider:
- Experience in similar projects
- Accreditations (NICEIC, ECA, etc.)
- Full insurance cover
- Health and safety record
- Financials
- Previous work

Knowing the difference between CAT A and CAT B fit outs is critical to successful project delivery. Whether in office or warehouse environments, each project requires technical requirements, operational needs and future flexibility. The secret to success is planning, choosing the right contractors, and communicating throughout the project. As buildings get more complex, the importance of professional electrical installation becomes more critical. Future trends will be:
- Smart building technology
- Sustainable
- Energy efficiency
- Flexible spaces
- Advanced security
By knowing these and working with the right contractors, property owners and tenants can get the most out of their fit-outs.
Need electrical contractors for your CAT A or CAT B fit out? Get in touch today.