Content last updated: February 2026
Every area of work or industry has its own language, and this can make it very difficult for people to understand and know what is being discussed. The construction and refurbishment industry is no exception.
This article identifies the differences between Commercial Cat A and Cat B fit-outs, so you can be more confident and knowledgeable as to the differences and what each entails.
Key Takeaways
- Cat A fit-outs provide a compliant, functional, and largely unfinished space that forms the foundation for occupation.
- Cat B fit-outs transform a Cat A space into a fully operational, branded, and ready-to-use workplace tailored to customer needs.
- The main distinction lies in customisation, with Cat A focusing on base building services and Cat B delivering interior design, finishes, and functionality.
- Most commercial office projects involve both stages, progressing from Cat A preparation to Cat B occupation.
What is Cat A Fit-Out?
Cat A is the very basic fit-out a commercial building undergoes during refurbishment. This is often described as the ‘empty shell’ phase. It includes essential elements necessary for occupancy. Therefore, it lacks any specific interior finishes or customisation.
The aim is to create a clean, compliant, and functional environment that can be marketed to prospective tenants.
Key Features of a Cat A Fit-Out:
- Cat A fit-outs include basic services such as electrical, lighting, plumbing, and heating/cooling systems. These services are installed up to a specified point but are not typically tailored to the customer’s needs. If the building is to have a lift, then work will be carried out to ‘house’ the facility at this stage.
- The space usually includes raised flooring and a suspended ceiling grid, providing flexibility for future configurations.
- Common areas like hallways, staircases, lifts, and toilets are part of Cat A fit-outs.
- Fire detection, smoke alarms and suppression systems are installed to meet building regulations.
- The walls are generally left unfinished or painted in a basic neutral colour. Floor coverings and finishes, such as carpet tiles or concrete screed, may be provided at a basic level.
Cat A fit-outs serve as a starting point for customers, allowing them to customise the space to meet their specific requirements.
What is a Cat B Fit-Out?
A Cat B fit-out transforms a space into a fully operational workplace tailored to the occupier. It builds on the Cat A foundation and introduces the elements that make the environment usable and distinctive.
This stage often includes meeting rooms, offices, breakout areas, tea points, specialist facilities, finishes, and furniture. It may also involve bespoke lighting, acoustic treatments, and technology integration. The focus shifts from infrastructure to experience, ensuring the space supports productivity, wellbeing, and organisational culture.
Key Features of a Cat B Fit-Out:
- Designing the layout, installing internal partitions, and creating individual offices, meeting rooms, open workspaces, reception areas, and any other required spaces. The design and materials are very often tailored to meet specific branding and functional requirements.
- The base building services provided in the Cat A fit-out may be modified or expanded to align with the customer’s specific needs. This includes electrical layouts, data cabling, HVAC zoning, and other services required for the customer’s operations.
- Cat B fit-outs include a wide range of finishes such as specific flooring materials, wall finishes, tailored ceiling treatments, lighting fixtures, and special fixtures and fittings.
- The customer is responsible for providing furniture, workstations, office equipment, and any other items required for their day-to-day operations.
What is the Difference Between Cat A and Cat B Fit-Out?
The key difference lies in purpose and level of completion. Cat A establishes the core infrastructure of a building, ensuring it is safe, compliant, and ready for occupation. Cat B, by contrast, is concerned with how the space functions for the people who use it.
In simple terms, Cat A provides the framework, while Cat B delivers the finished workplace. Together, they form a structured approach to fit out, moving from base build preparation to a fully realised environment designed around the needs of the occupier.
Delivering Cat A and Cat B with Confidence
Whether you are preparing a space for market through a Cat A fit-out or creating a tailored environment with a Cat B scheme, Willmott Dixon Interiors brings the experience and insight to guide you at every stage.
“Cat A and Cat B fit outs each play a distinct role in bringing a workplace to life. Cat A establishes the core infrastructure and performance of a space, creating a compliant and flexible foundation. Cat B is where the environment becomes tailored to the occupier, reflecting culture, supporting productivity, and enabling long term value. Our role is to guide clients through both stages with clarity and expertise, ensuring the finished space is not only functional, but fit for the future.”
– Adam Worrall, Willmott Dixon Interiors Managing Director
Willmott Dixon Interiors is a fit out company with extensive experience across a wide range of commercial projects. If you have a Cat A or Cat B question or project in mind, please contact us today.