What Is the Difference Between Cat A and Cat B Office Fit Out?

A Cat A office fit out prepares a commercial space to a basic functional standard, usually for landlords or developers. A Cat B office fit out turns that space into a finished workplace for the occupier, including meeting rooms, furniture, branding, finishes, kitchens, technology and the final office interior design.

In simple terms:

• Cat A fit out = the space is usable but not personalised

• Cat B fit out = the space is ready for the business to move in and work from

For London businesses, landlords and tenants, understanding this difference is important because it affects cost, programme, lease negotiations, responsibility and the final workplace experience.

Why Cat A and Cat B Fit Out Searches Matter

Searches around Cat A office fit out, Cat B office fit out, office interior fit out and office design and fit out are often made by people close to making a commercial property decision.

They may be:

• landlords preparing a space for the market

• tenants comparing different office options

• businesses planning a relocation

• occupiers upgrading an existing workplace

• facilities teams managing commercial refurbishment

• property managers reviewing fit out responsibilities

This is why the topic matters commercially. People are not just looking for definitions. They are trying to understand what type of project they need, who pays for what and what should be included before signing off the works.

What Is a Cat A Office Fit Out?

A Cat A office fit out is usually the base-level fit out of a commercial office space.

It creates a functional internal environment but does not normally include the occupier’s final layout, furniture, branding or specialist workplace features.

A Cat A office fit out may include:

• raised access floors

• suspended ceilings

• basic floor finishes

• mechanical and electrical services

• lighting

• fire detection systems

• air conditioning or ventilation infrastructure

• toilets and core facilities

• basic internal walls

• compliant escape routes

• landlord-controlled systems

Cat A fit outs are commonly delivered by landlords, developers or commercial property owners to make a space ready for prospective tenants.

However, the exact scope can vary significantly between buildings, leases and landlords. That is why tenants should always ask what “Cat A” actually includes before making assumptions.

What Is a Cat B Office Fit Out?

A Cat B office fit out is the occupier-specific stage.

This is where the office becomes a usable, branded and functional workplace.

A Cat B office fit out may include:

• reception areas

• meeting rooms

• private offices

• open-plan workstations

• breakout spaces

• kitchen and tea point areas

• furniture

• floor finishes

• feature lighting

• branded decoration

• acoustic treatments

• collaboration zones

• storage

• AV equipment

• data and power layouts

• signage

• final finishes

If Cat A is the blank canvas, Cat B is the working office.

For most businesses, Cat B is where the real workplace value is created because the space is shaped around people, operations, clients and company culture.

Cat A vs Cat B Fit Out: Quick Comparison

What Is Office Interior Fit Out?

Office interior fit out is the practical process of shaping the internal office environment.

It may include both design and construction elements, such as:

• layout planning

• finishes

• partitions

• ceilings

• lighting

• flooring

• joinery

• furniture

• decoration

• data and power

• staff facilities

• meeting rooms

• compliance improvements

This phrase is often used by businesses looking for a complete service that covers both how the office looks and how it works.

A successful office interior fit out should improve:

• staff productivity

• visitor experience

• space efficiency

• comfort

• acoustic performance

• collaboration

• flexibility

• brand presentation

• long-term maintenance

The British Council for Offices notes that its latest Guide to Fit-Out supports office interior design for occupiers and built environment professionals, with guidance shaped by changing work trends and environmental demands. This reflects why modern office fit outs are now about more than appearance. They need to respond to hybrid working, wellbeing and sustainability.

What Is Office Design and Fit Out?

Office design and fit out combines workplace planning with physical delivery.

That means the project should consider both:

1. How the office should work 2. How the works will be delivered

A design-only approach may create an attractive concept but fail to consider cost, sequencing, compliance or construction practicalities.

A build-only approach may complete the works but miss the opportunity to improve how the business uses the space.

A joined-up office design and fit out process should review:

• how many people use the office

• how hybrid working affects occupancy

• where meetings happen

• where private calls take place

• how teams collaborate

• how visitors are welcomed

• where storage is needed

• how building services support the layout

• what compliance works are required

• how disruption will be managed

This is especially important in London, where offices are often occupied, access can be restricted and programmes need careful coordination.

Which Fit Out Type Do You Need?

The right fit out depends on who you are and what stage the building is at.

Landlords Usually Need Cat A Fit Out When:

• a space is being prepared for lease

• an older office is being brought back to market

• base building services need refreshing

• the space needs to appeal to multiple tenant types

• compliance needs to be improved before marketing

Tenants Usually Need Cat B Fit Out When:

• moving into a new office

• adapting a space to their team

• installing workstations and meeting rooms

• creating client-facing areas

• adding branding and final finishes

• making the office ready for occupation

Existing Occupiers May Need Office Refurbishment When:

• the team is staying in the same premises

• the layout no longer works

• the office feels tired

• hybrid working has changed space requirements

• building services need upgrading

• the business wants to avoid relocation

Why Cat A and Cat B Fit Out Scopes Must Be Clear

One of the biggest causes of confusion is unclear scope.

A tenant may assume a landlord is providing certain items. A landlord may assume the tenant will take responsibility after handover. A contractor may price based on limited information.

This can create disputes around:

• lighting

• flooring

• mechanical systems

• electrical capacity

• fire doors

• fire stopping

• kitchen facilities

• meeting rooms

• decoration

• data infrastructure

• furniture

• handover documentation

Before works begin, it should be clear what is included, who is responsible and what level of finish is expected.

Compliance Considerations for Cat A and Cat B Fit Out

Office fit out projects are not just design projects. They are construction projects and can affect health, safety and building compliance.

Important areas to consider include:

• fire risk assessment findings

• fire doors

• fire stopping

• escape routes

• emergency lighting

• electrical safety

• ventilation

• accessibility

• CDM duties

• welfare facilities

• landlord approvals

GOV.UK guidance explains that the responsible person for workplace fire safety must carry out and regularly review a fire risk assessment, tell staff about risks and maintain appropriate fire safety measures.

CDM Duties During Office Fit Out Projects

Commercial office fit out works usually fall under construction health and safety requirements.

The HSE explains that commercial clients have duties under CDM 2015 and must make suitable arrangements for managing a project so construction work can be carried out without risks to health and safety.

For businesses appointing an office fit out contractor, this means the project should be planned properly from the start.

Key questions include:

• has enough information been provided about the building?

• are the contractors suitable for the works?

• has the programme allowed enough time?

• are staff, visitors or neighbouring tenants affected?

• are risks being managed during the works?

• is there a clear handover process?

This is particularly important for live office environments where people may remain in the building during the project.

What Should Be Checked Before Starting a Cat B Fit Out?

Before a Cat B fit out begins, review:

1. The Existing Cat A Condition

Check whether the base building is genuinely ready for fit out.

Review:

• lighting

• ceilings

• floors

• ventilation

• electrical capacity

• fire safety systems

• toilets

• landlord areas

2. The Lease and Landlord Requirements

Confirm:

• what works are permitted

• what approvals are required

• who owns which elements

• reinstatement responsibilities

• access restrictions

• insurance requirements

3. Workplace Requirements

Assess:

• desk numbers

• meeting room needs

• call spaces

• kitchen facilities

• reception needs

• storage

• breakout areas

• future growth

4. Building Services

Confirm whether the existing services support the planned layout.

This includes:

• electrical loads

• data requirements

• ventilation

• heating and cooling

• plumbing

• lighting controls

Common Mistakes in Cat A and Cat B Office Fit Outs

Assuming All Cat A Spaces Are the Same

They are not.

One Cat A space may be nearly ready for tenant fit out. Another may need significant upgrading before it can support the intended layout.

Leaving Building Services Too Late

Furniture and finishes often get attention first, but services determine whether the office will function properly.

Ignoring Fire Safety Until the End

Fit out works can affect fire doors, escape routes, compartmentation and emergency lighting. These should be considered early.

Underestimating Acoustic Needs

Hybrid work has increased video calls and private meetings. Poor acoustics can quickly make a new office frustrating to use.

Choosing Finishes Before Confirming Practical Requirements

A design may look good, but the office still needs to support daily operations, compliance, storage, technology and maintenance.

Cat A and Cat B Office Fit Out Checklist

Use this checklist before committing to works:

• Confirm whether the project is Cat A, Cat B or refurbishment-led

• Define who is responsible for each element

• Review the lease and landlord requirements

• Survey the existing condition

• Check fire safety and compliance requirements

• Confirm mechanical and electrical capacity

• Review ventilation and comfort

• Agree the workplace brief

• Confirm furniture and technology needs

• Plan for staff disruption if occupied

• Agree programme, access and handover

• Make sure the specification is clear before pricing

Why London Businesses Need a Practical Fit Out Partner

London office fit out projects often involve more than interiors.

They may require:

• occupied building planning

• out-of-hours working

• landlord coordination

• access management

• multiple trades

• compliance upgrades

• tight programmes

• phased delivery

• careful communication

That is why businesses should look beyond surface-level design and choose a contractor that understands commercial environments.

Final Thoughts

Understanding the difference between Cat A office fit out and Cat B office fit out helps landlords, tenants and businesses make better decisions before work begins.

Cat A prepares the commercial space. Cat B turns it into a workplace.

For London businesses, the most successful projects usually combine clear scope, practical office interior fit out, compliance checks, realistic programme planning and a contractor who understands live commercial buildings.

Barry Turner and Son Ltd supports commercial clients with office refurbishment, office fit out, fire doors, fire stopping, electrical services, HVAC, plumbing, decorating and wider building upgrade works across London and the South East.

To discuss a Cat A, Cat B or refurbishment-led office project, visit Commercial Services or request a Free Quotation.

FAQ

What is a Cat A office fit out?

A Cat A office fit out prepares a commercial space to a basic functional standard, usually including floors, ceilings, lighting, mechanical and electrical services and core building systems.

What is a Cat B office fit out?

A Cat B office fit out creates the final workplace for the occupier. It may include meeting rooms, workstations, furniture, finishes, kitchens, branding, technology and final decoration.

What is the difference between Cat A and Cat B fit out?

Cat A is the base fit out, usually landlord-led. Cat B is the occupier-specific fit out that makes the office ready to use.

Who pays for Cat A and Cat B fit out?

This depends on the lease, landlord agreement and project structure. Cat A is often landlord-led, while Cat B is usually tenant-led, but responsibilities should always be confirmed in writing.

What is office interior fit out?

Office interior fit out is the process of designing and delivering the internal workplace, including layout, finishes, partitions, furniture, lighting, power, data and staff facilities.

Is office design and fit out the same as refurbishment?

Not always. Office design and fit out usually creates or adapts a workspace, while refurbishment upgrades an existing office. Many projects include elements of both.

Can a Cat B fit out be done in an occupied office?

Yes, but it needs careful phasing, access planning, health and safety controls and communication to reduce disruption.

Why is fire safety important during office fit out?

Fit out works can affect escape routes, fire doors, compartmentation and emergency systems, so fire safety should be reviewed before work begins.

Do CDM duties apply to office fit out projects?

Yes. Commercial clients have duties under CDM 2015 when construction work is carried out, including making suitable arrangements for managing the project safely.

How do I know which fit out type my business needs?

If you are preparing a space for lease, you may need Cat A. If you are creating a workplace for your team, you probably need Cat B. If you are improving an existing office, you may need refurbishment.