A Simple Guide to Commercial Fit Out Terms

Commercial fit out language can be useful, but it is not always as clear as it sounds.

Terms like CAT A, CAT A+, CAT B, turnkey and shell and core are often used early in a project, usually before the design, budget and programme are fully understood. They can help everyone talk about the same broad stages of a space, but they can also create confusion if the actual scope is not clearly defined.

The important thing to remember is this: the label matters less than the detail behind it.

A space described as CAT A in one building may not include the same things as CAT A in another. A “move in ready” workspace may still need additional furniture, data, branding or operational items before anyone can actually use it. A turnkey space may be ready in principle, but still need careful checking against the needs of the occupier.

This guide explains some of the most common commercial fit out terms in plain English.

Shell and core

Shell and core usually describes a building or unit that is structurally complete, but not yet fitted out internally for occupation.

It may include the main structure, external envelope, lifts, stair cores, risers and incoming services infrastructure. However, the individual tenant areas are often left unfinished.

In simple terms, the space exists, but it is not ready to use.

Shell and core can be common in new developments, larger commercial buildings, retail units and hospitality spaces where the final occupier will take responsibility for their own fit out.

CAT A

CAT A is usually the landlord’s base finish.

It is intended to make a commercial space lettable and ready for a tenant to fit out. This might include items such as raised floors, ceilings or exposed services, lighting, basic mechanical and electrical services, fire alarm provision, decorated perimeter walls and other landlord finishes.

The exact specification can vary from building to building.

A CAT A space is not usually designed around a specific occupier. It is more of a blank canvas. It should give the tenant a clean, functional starting point for their own fit out.

In simple terms, CAT A is generally ready for the next layer of design, but not fully ready for a business to move in and operate.

CAT A+

CAT A+ sits somewhere between CAT A and CAT B.

It is usually a more complete landlord fit out, designed to make a space feel more ready for occupation. This can be useful for tenants who want a quicker, simpler move, or for landlords who want to reduce the amount of decision making and upfront work needed from potential occupiers.

CAT A+ might include meeting rooms, a tea point, floor finishes, desks, chairs, lighting, soft seating, planting and basic power and data provision.

It is often described as “plug and play” or “semi fitted”.

However, this is where the grey area starts. CAT A+ is not always defined in the same way. One landlord’s CAT A+ might be a fully furnished workspace. Another might be a lightly dressed suite with only some basic facilities included.

The key question is not just whether a space is called CAT A+. The key question is what is actually included.

CAT B

CAT B is the occupier specific fit out.

This is the layer that makes the space work for the people, brand and operation using it. In an office, that could include the final layout, meeting rooms, furniture, kitchens, tea points, finishes, feature lighting, joinery, AV, signage, storage, branding and staff facilities.

In retail, hospitality or leisure, CAT B may include much more specialist design and operational detail, such as customer journey, back of house planning, counters, changing rooms, bars, kitchens, display systems, lighting scenes and brand specific finishes.

CAT B is where the space becomes more tailored.

In simple terms, CAT B is the fit out that turns the space into somewhere specific people can actually use.

CAT C

CAT C is less universally used, but it is sometimes used to describe the final move in layer.

This can include loose furniture, artwork, accessories, styling, plants, equipment and other items that complete the space.

Because CAT C is not as consistently defined as CAT A or CAT B, it is worth being very clear about what is included. For some teams, furniture might sit within CAT B. For others, it might be treated as a separate CAT C package.

Again, the label is less important than the scope.

Turnkey

Turnkey usually means a space is delivered ready to use.

In theory, the occupier should be able to move in, turn the key and start operating.

In practice, it is worth checking exactly what “ready” means. Does it include furniture? IT? AV? signage? accessories? operational equipment? final cleaning? staff areas? storage? brand elements?

Turnkey can be a very useful delivery route, especially for clients who want one team to take responsibility for a complete outcome. But the scope still needs to be carefully agreed.

Plug and play / Fitted & Furnished

Plug and play or fitted and furnished is often used for flexible workspace, serviced offices and CAT A+ suites.

It usually suggests that the basics are already in place, such as desks, chairs, meeting rooms, power, data, WiFi, tea points and shared amenities.

The idea is that a tenant can move in quickly without needing to manage a full fit out themselves.

As with turnkey, it is worth checking what is actually included, what is shared, what is private and what still needs to be added.

Base build

Base build refers to the existing building and its main systems before the tenant specific fit out is added.

This can include the structure, external envelope, roof, core areas, risers, main mechanical and electrical infrastructure, life safety systems and other landlord controlled elements.

Understanding the base build is important because it sets the limits of what can be done easily, what needs coordination and what may trigger additional approvals.

Demise

The demise is the area included within the lease.

In simple terms, it is the part of the building the tenant is actually taking.

This matters because it affects responsibility. Some areas may sit inside the tenant demise, while others may remain under landlord control. This can influence maintenance, alterations, signage, services, access, fire strategy and permissions.

Common parts

Common parts are shared areas outside the tenant demise.

These might include receptions, corridors, WCs, lift lobbies, stairs, shared lounges, cycle stores and other communal facilities.

Common parts can have a big impact on how a building feels. They are often the first and last spaces people experience, so they can strongly influence perceived quality, tenant confidence and the overall value of the building.

Test fit / Space Plan

A test fit is an early space planning exercise.

It is usually used to check whether a space can accommodate a particular use, number of people, layout, operational requirement or commercial target.

For an office, a test fit might explore desk numbers, meeting room provision, breakout space, storage and circulation. For retail or hospitality, it might explore customer flow, back of house, covers, sales area, counters or service points.

A good test fit is not just about making things fit on paper. It should help identify whether the space works in practice.

Feasibility

Feasibility is a broader early stage review of whether a project is viable.

This can include space planning, budget, programme, statutory requirements, planning, building control, services, access, heritage constraints, landlord requirements and operational needs.

Feasibility work is useful because it helps identify the key opportunities and risks before too much time or money is committed.

Why these terms matter

Commercial fit out terms are useful shorthand, but they should never replace a clear scope.

Before a project is priced, programmed or designed in detail, everyone should understand what is included, what is excluded, who is responsible and what still needs to be decided.

This matters because unclear scope can affect cost, programme, design quality and expectations. It can also create gaps between what a landlord thinks they are providing, what a tenant thinks they are receiving and what the project team is actually delivering.

A space might be finished, but not usable.
It might be lettable, but not occupier ready.
It might be described as turnkey, but still need important decisions before anyone can move in properly.

The best starting point is always clarity.

Not just the label, but the detail behind it.