Published on:

30 May 2024

Updated on:

30 May 2024

Read time:

1 minute

Max Parsons

Project Director

Cyril Parsons

Managing Director

When it comes to an office fit out, businesses often face a crucial decision: should they opt for a Category A (Cat A) fit out or a Shell and Core fit out?

Understanding the differences between these two options is essential for making an informed choice that aligns with the company's goals, budget, timescales and needs. In this article, we'll provide a detailed comparison of Cat A and Shell and Core fit outs, outlining their definitions, features, as well as their pros and cons.

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What is a Shell and Core fit out?

A Shell and Core fit out refers to the basic structure of a property before any interior work takes place. It includes the core concrete and metal framework, structural elements like columns and elevator shafts, the external facade (windows and/or curtain walling) and weatherproofing, and initial utilities and plumbing.

Essentially, a Shell and Core space is a bare construction site without lighting, flooring, or mechanical systems. It establishes the fundamental supports and bones of the property, upon which the fit out process can build to create customised interiors.

What is included in a Shell and Core fit out?

While the specifics may vary, a typical Shell and Core fit out includes:

  • The core concrete and metal framework
  • Structural elements like columns and elevator shafts
  • External facade and weatherproofing
  • Initial utilities, plumbing and drainage
  • In-coming power supply and distribution board

Shell and Core Pros:

  • Allows for maximum flexibility in layout and design
  • Enables tenants to customise the space to their specific needs and requests
  • May be more cost-effective for long-term leases
  • There is often a cost contribution from the landlord/developer to enable the occupier to fit it out to a Cat A specification.

Shell and Core Cons:

  • Requires additional work and investment to make the space functional
  • Longer timeline for occupancy due to the need for a complete fit out
  • May not be suitable for companies with limited budgets or short-term leases

What is a Cat A office fit out?

A Cat A fit out takes a Shell and Core space and adds the core services needed to make it habitable. However, at this stage, the environment remains a "blank canvas" without custom elements like kitchens, breakout areas, or meeting rooms.

Additional work through a Cat B fit out is required to create a fully functioning office space design tailored to the tenant's needs.

What is included in a CAT A fit out?

While there's no industry standard, but Cat A spaces typically contain:

  • Raised floors and suspended ceilings (with basic finish)
  • Basic mechanical, electrical, and HVAC services
  • Fire detection systems and smoke alarms
  • Minimal finishes on walls
  • Lighting, air conditioning, and bathrooms
  • Core area toilets and shower facilities

A Cat A fit out provides the bare minimum for occupancy but lacks the specialised design and amenities needed for the space to operate as a workplace.

Cat A Pros:

  • Provides a habitable space with core services installed
  • Offers a "blank canvas" for tenants to customise through a Cat B fit out
  • Shorter timeline for occupancy compared to Shell and Core

Cat A Cons:

  • Limited flexibility in layout and design due to pre-installed services
  • Additional investment required for a Cat B fit out to create a fully functional office
  • May not align with the tenant's specific needs or brand identity


Understanding the differences between Cat A and Shell and Core fit outs is crucial for companies looking at an office refurbishment project. Ultimately, the choice between a Cat A and Shell and Core fit out depends on factors such as the company's goals, budget, timeline, and desired level of customisation.

By carefully considering these pros and cons and consulting with experienced office fit out professionals, companies can make an informed decision that best suits their needs and sets them up for long-term success in their new office space.

Meet the Authors

Responsible for the day-to-day management of a project, Max provides the interface between the internal teams, addressing the client’s needs to make sure they are always considered and that objectives and standards are consistently met.

A founding partner of Office Principles, Cyril has over 30 years’ experience in workplace design and has been instrumental in the success of the business and its positioning as a leading workplace consultancy. An author of white papers and a renowned industry speaker, who regularly hosts his own popular seminars and webinars, thought leader Cyril’s book on office relocation and fit out, The Black Book, is currently on its fourth edition.