A Cat B fit out is the second phase of commercial interior work, building on the landlord’s base building (Cat A) to create a finished, tenant-ready space. It includes all partitioning, mechanical & electrical services, flooring, decorative finishes, lighting & power distribution, and bespoke elements like reception desks or treatment rooms. The distinction between Cat A & Cat B determines your budget, timeline & specification responsibility.
How does Cat B differ from Cat A?
The commercial property industry divides fit out into two legal & financial phases. Cat A (Category A) is the landlord’s responsibility: a stripped, weathertight shell with basic structural services (risers, distribution routes). Cat B (Category B) is the tenant’s scope: everything from the partition wall inwards, including mechanical heating & cooling, all electrical outlets & distribution boards, floor coverings, wall finishes, lighting design, joinery, and any specialist requirements like dental surgeries or salon treatment areas.
Understanding this boundary is crucial because it governs cost accountability, project risk, and specification detail. When a studio approaches Discovery for a commercial project, the first task is establishing what the landlord has delivered (Cat A) & what must be designed & commissioned as Cat B. The Beaulieu Dental Practice, Fruittii Hair Salon, Keystones Estate Agent & Tone at Canary Wharf all involved Cat B scopes because each required bespoke treatment rooms, client spaces, or operational layouts that go far beyond a bare shell.
What does a Cat B scope typically include?
Cat B covers the full interior specification from floors to ceilings & walls. This includes partition walls (to create rooms or zones), mechanical & electrical services (heating, cooling, power circuits, data routes), all lighting design & installation, door sets & hardware, floor finishes (whether carpet, timber, resin or terrazzo), wall decoration & paint, ceiling treatments, joinery & cabinetry, signage, and all soft furnishings or moveable elements. It also includes the design & specification of any bespoke built-in features: treatment chairs in a salon, reception counters, kitchen facilities, or storage systems.
The scope is not standardised across projects. A fitness studio requires different mechanical & electrical infrastructure than a dental practice, which requires different acoustic & infection-control specifications than a hair salon. This is why the Concept, Design & Specification stage is the studio’s longest phase: the brief, the building’s constraints, planning regulations, & the tenant’s operational needs all dictate what Cat B actually means on paper.
Why does Cat B matter to your project cost & timeline?
Cat B is a tenant’s largest expenditure in a lease. Because you are responsible for its design, specification, & execution, the clarity of your brief & the quality of your design documentation directly affect cost predictability & delivery speed. A poorly specified partition will require rework; an electrical strategy designed without input from your operations team will force costly relocations mid-project; a finish schedule that conflicts with the Cat A base will create delays. The studio’s process — particularly the Discovery & Concept phases — exists to prevent these failures by translating your operational needs into a coherent specification that contractors can price & execute accurately.
The timeline for Cat B also depends on whether the Cat A works are complete & dry before you begin. Many commercial tenants discover late that the landlord’s schedule delays their fit out start; a detailed Concept & Concept, Design & Specification stage allows parallel planning so you can start the moment the space is ready. Projects like Tone at Canary Wharf & Keystones Estate Agent benefited from this foresight: specification & procurement were complete before site access, so the Commission phase ran without friction.
What does the design & specification process look like for Cat B?
The studio’s approach to Cat B begins in Discovery: understanding your business model, your client journey, your operational constraints, & the building’s structural & services reality. This informs the Concept phase, where spatial layout, material palette & service strategy are tested & agreed. Then the Concept, Design & Specification stage produces the detailed drawings, specifications, & schedules that contractors will price & build from: floor plans showing partition locations & door swings; reflected ceiling plans showing lighting & mechanical distribution; electrical plans with outlet & circuit detail; finishes schedules specifying paint, flooring, wall coverings by room; & joinery drawings for bespoke elements.
This specificity is not bureaucratic overhead; it is protection & clarity. A contractor cannot price ambiguity, & clients cannot budget for vague scopes. The Beaulieu Dental Practice & Fruittii Hair Salon required particularly rigorous specification because their treatment areas involved fixed equipment, specialized finishes (for hygiene & durability), & compliance with healthcare & salon regulations. The design documentation became the contract record that both the studio & the contractor referenced throughout the Commission phase.
How do you know if Cat B is right for your brief?
Every commercial lease will involve some Cat B work. The question is not whether you need it, but how deep your scope runs. A small office space might need only partition walls, redecoration, & new power distribution (light Cat B). A salon, dental surgery, or hospitality venue requires full mechanical & electrical design, bespoke treatment areas, & specialist finishes (substantial Cat B). The landlord’s Cat A offer also shapes your scope: some landlords deliver more (e.g. raised floors, full electrical distribution, HVAC ready-to-connect) which reduces Cat B; others deliver only the minimum, expanding your responsibility.
The clearest way to establish your actual scope is to obtain the Cat A specification from the landlord before committing to your fit out budget or timeline. Then engage a designer early in Discovery to audit the space against your operational brief & build a realistic Cat B scope & cost model. This is the work that protects tenants from budget creep & schedule shock. Projects like Keystones Estate Agent started with this conversation: what has the landlord delivered, what does the business need, & what must be designed & built as Cat B?
What questions should you ask before you start your Cat B fit out?
Before the Commission phase begins, you should be able to answer these questions with confidence: What exactly did the landlord deliver in Cat A (obtain the Cat A specification document)? What is your operational brief (how will the space be used, who uses it, what equipment must be accommodated)? What is your budget & can it be baselined against the design specification? What is the landlord’s program & when will Cat A be complete & dry? Are there any planning or compliance constraints (disability access, fire safety, heritage restrictions)? Who will be responsible for mechanical & electrical design (the studio, a MEP consultant, the contractor)? How will change & contingency be managed during the build?
A studio works through these questions in the Discovery & Concept phases & ensures the Concept, Design & Specification documentation reflects the answers. This is why the early phases matter so much. Once you move into Commission, the specification becomes fixed & changes become expensive. The residential projects London Embankment Apartment & Witham Project followed the same discipline at smaller scale: clarity up front, execution without friction, a finished interior that works as intended & endures.