A commercial fit-out is one of the most significant investments a business makes. Get it right and you have a workspace that supports productivity, reflects your brand, and holds its value. Get it wrong and you are looking at cost overruns, programme delays, and a defects list that drags on for months after you move in.
Most of the problems we see on commercial fit-outs are not caused by bad contractors or poor materials. They come from a lack of clarity about what happens at each stage — who is responsible for what, when decisions need to be made, and what the consequences are of leaving things too late.
This guide walks through the eight stages of a commercial fit-out as TCM runs them, with honest notes on the points where projects most often go wrong. Whether you are fitting out a new office, refurbishing a retail unit, or taking on a shell-and-core space, the process is broadly the same — though the timescales and complexity vary considerably.
What this guide covers
CAT A and CAT B fit-outs for offices, retail units, and mixed-use commercial premises in Hertfordshire and North London. If you are planning a commercial refurbishment of an existing occupied space, see our guide to commercial refurbishment services.
CAT A vs CAT B: Understanding the Starting Point
Before we get into the stages, it is worth clarifying the terminology, because it causes confusion on almost every project.
A CAT A fit-out brings a shell-and-core space to a basic functional standard. Think raised floors, suspended ceilings, M&E distribution to floor and ceiling level, and perimeter trunking. It is typically the landlord's responsibility and creates a blank canvas for the tenant.
A CAT B fit-out is the tenant's fit-out. This is where the space becomes yours: partitioning, kitchen and welfare, reception, branding, specialist lighting, furniture, IT and AV infrastructure. Most commercial clients engage TCM for CAT B works, though we also carry out combined CAT A and CAT B programmes where the landlord has not completed the base build to the required standard.
| Element | CAT A (Landlord) | CAT B (Tenant) |
|---|---|---|
| Raised floors / screeds | ✓ | — |
| Suspended ceilings | ✓ | — |
| M&E distribution | ✓ | — |
| Partitioning | — | ✓ |
| Kitchen / welfare | — | ✓ |
| Reception / branding | — | ✓ |
| Specialist lighting | — | ✓ |
| IT / AV infrastructure | — | ✓ |
| Furniture | — | ✓ |
The Eight Stages of a Commercial Fit-Out
Initial Survey and Brief
Week 1–2The process starts with a measured survey of the space and a detailed brief. TCM's project manager walks the site with you to understand your operational requirements — headcount, departmental adjacencies, IT infrastructure, welfare facilities, and any brand standards. This is also when we identify constraints: existing M&E services, structural elements that cannot be moved, landlord restrictions, and CDM obligations.
From Our Experience
One thing clients often underestimate at this stage is the importance of getting the landlord's licence to alter in place early. Waiting until design is complete can add 4–6 weeks to the programme. We flag this at the first meeting.
Design and Specification
Weeks 2–5With the brief confirmed, the design team produces space plans, elevations, and a full specification. For CAT B works, this covers partition layouts, ceiling design, lighting scheme, flooring, joinery, kitchen and welfare, and IT/AV infrastructure. The specification document is the contract reference — it defines materials, finishes, and performance standards so there are no surprises at the end.
From Our Experience
The most common design-stage mistake we see is under-specifying the M&E. Clients focus on the visible finishes and leave the mechanical and electrical to be 'sorted later'. This almost always leads to programme delays and cost increases. We insist on a complete M&E specification before tendering.
Regulatory Approvals and Landlord Consent
Weeks 3–6 (parallel with design)Most commercial fit-outs require building regulations approval for M&E works, structural alterations, and fire safety upgrades. If the works change the use class or affect the external appearance, planning permission is also needed. Landlord consent — the licence to alter — is a separate process and must be obtained before works begin. TCM prepares the licence to alter package and liaises with the landlord's surveyor to keep this moving.
From Our Experience
In our experience, landlords in Hertfordshire and North London typically take 3–6 weeks to grant a licence to alter once the package is submitted. Starting this process at design stage rather than after tender is one of the most effective ways to protect the programme.
Tender and Contract Award
Weeks 4–6Once the design and specification are complete, TCM prepares a fixed-price contract sum. For larger projects, we may tender specialist packages (AV, data, bespoke joinery) to ensure best value. The contract sets out the programme, payment schedule, change-order procedure, and defects liability period. We use JCT Minor Works or a bespoke contract depending on project value.
From Our Experience
Fixed-price contracts protect you from cost creep, but only if the specification is complete. Vague specifications lead to provisional sums, which become the source of most commercial disputes. We will not issue a fixed price against an incomplete specification.
Pre-Construction and Mobilisation
1–2 weeks before start on siteBefore work begins, TCM completes a Construction Phase Plan (required under CDM Regulations for most commercial projects), orders long-lead items (bespoke joinery, specialist lighting, raised floor systems), and agrees the site logistics plan with the building manager. Access arrangements, delivery windows, and waste management are all confirmed in writing.
From Our Experience
Out-of-hours working is common on commercial fit-outs, particularly for noisy or disruptive phases like demolition, concrete cutting, and first-fix M&E. We agree the out-of-hours programme with the building manager and your team before mobilising — not on the day.
Construction Phase
Varies by scope (typically 6–12 weeks)The construction phase follows a logical sequence: strip-out and demolition first, then structural works if required, followed by first-fix M&E (containment, cabling, ductwork), partitioning and ceilings, second-fix M&E (devices, luminaires, grilles), joinery installation, floor finishes, decoration, and finally furniture and IT. TCM's site manager produces a weekly progress report with photographs so you always know where the project stands.
From Our Experience
The phase clients most often misunderstand is second-fix M&E. It looks like not much is happening — the electricians are fitting sockets and the HVAC engineers are commissioning units — but this is actually the most technically complex phase. Rushing it is where defects originate.
Commissioning and Testing
Final 1–2 weeksBefore handover, all M&E systems are commissioned and tested: HVAC balancing, lighting control programming, fire alarm testing, emergency lighting testing, and data infrastructure testing. Building control inspects the works and issues a completion certificate. TCM's site manager carries out a pre-handover snagging inspection and resolves all items before the client walkthrough.
From Our Experience
We carry out our own internal snagging before inviting the client to the formal handover. The client's snag list is typically very short as a result — usually cosmetic items only. This is deliberate: we would rather find and fix issues ourselves than have them raised at handover.
Handover and Post-Completion
Handover day + 12-month defects periodAt handover, TCM provides a complete O&M manual covering all installed systems, test certificates, warranties, and as-built drawings. The defects liability period (typically 12 months) begins at practical completion — any defects that emerge during this period are rectified by TCM at no additional cost. We also offer ongoing commercial maintenance contracts to keep the fit-out in peak condition.
From Our Experience
The O&M manual is often treated as a formality, but it is genuinely important. When a system fails two years after handover, the manual tells the facilities manager exactly who installed it, what the service schedule is, and who to call. We invest time in making ours comprehensive.
Typical Programme by Fit-Out Type
Programme durations vary significantly by scope and size. The table below shows typical overall durations from survey to handover for the most common commercial fit-out types TCM delivers in Hertfordshire and North London.
| Fit-Out Type | Typical Size | Survey to Handover | Construction Phase |
|---|---|---|---|
| Small office (CAT B) | 500–1,500 sq ft | 8–12 weeks | 4–6 weeks |
| Medium office (CAT B) | 2,000–5,000 sq ft | 12–18 weeks | 8–12 weeks |
| Large office (CAT B) | 5,000+ sq ft | 18–28 weeks | 12–18 weeks |
| Retail unit | 500–3,000 sq ft | 6–12 weeks | 4–8 weeks |
| Restaurant / hospitality | 1,000–4,000 sq ft | 14–22 weeks | 10–14 weeks |
| Combined CAT A + CAT B | Any | Add 4–8 weeks to above | Add 3–6 weeks |
The Most Common Causes of Programme Delay
In our experience managing commercial fit-outs across Hertfordshire and North London, the same causes of delay appear repeatedly. None of them are inevitable — all can be managed with good pre-construction planning.
Licence to alter delays
Landlords take time to review and approve the licence to alter. Starting this process at design stage rather than after tender typically saves 4–6 weeks. We prepare the licence package and chase the landlord's surveyor proactively.
Incomplete specification at tender
Tendering against a partial specification leads to provisional sums, which become the source of cost and programme uncertainty. We will not issue a fixed price against an incomplete specification.
Long-lead item ordering
Bespoke joinery, specialist lighting, raised floor systems, and some HVAC equipment have lead times of 6–12 weeks. Ordering these before construction begins is essential. We identify long-lead items at the design stage and order them as soon as the contract is signed.
IT and AV scope creep
IT and AV requirements often expand during construction as the client's team gets more involved. Agreeing the IT and AV specification in full before construction begins avoids late changes that affect the M&E programme.
Building control delays
Building control inspections are required at specific stages. Scheduling these in advance and ensuring the works are ready for inspection avoids waiting time. We coordinate with the building control inspector throughout the programme.
Frequently Asked Questions
How long does a commercial fit-out take?+
A typical CAT B office fit-out for a 2,000–5,000 sq ft space takes 8–14 weeks from survey to handover. Retail fit-outs can be faster — 4–8 weeks — because the scope is usually more defined. The programme depends on the complexity of M&E works, bespoke joinery lead times, and whether the space requires structural alterations. TCM provides a detailed programme at the pre-construction stage so you know exactly when each phase completes.
What is the difference between CAT A and CAT B fit-out?+
A CAT A fit-out brings a shell-and-core space to a basic functional standard — raised floors, suspended ceilings, M&E distribution, and perimeter trunking. It is typically the landlord's responsibility. A CAT B fit-out is the tenant's fit-out: partitioning, kitchen, reception, branding, furniture, and all the elements that make the space work for your business. Most commercial clients engage TCM for CAT B works, though we also carry out combined CAT A and CAT B programmes.
Do I need planning permission for a commercial fit-out?+
Internal fit-outs that do not alter the building's external appearance or change its use class generally fall within permitted development and do not require planning permission. However, if you are changing the use of the premises (for example, from office to retail), installing a new shopfront, or making external alterations, planning permission will be required. Building regulations approval is almost always needed for M&E works, structural alterations, and fire safety upgrades. TCM's pre-construction team advises on regulatory requirements at the survey stage.
Can the fit-out be carried out while we are still trading?+
Yes, in many cases. TCM has extensive experience in phased fit-outs that allow businesses to continue operating during construction. We sequence works to minimise disruption — typically completing the noisiest and dustiest phases out of hours or over weekends, then moving to quieter finishing works during business hours. A detailed phasing plan is agreed before works begin so you know exactly when each area will be affected.
What should I check at the handover inspection?+
At handover, check that all M&E systems are commissioned and working (lighting, HVAC, data, fire alarm), all joinery and partitioning is complete and snag-free, all finishes match the specification, and all statutory documentation is in order (building control sign-off, O&M manuals, test certificates). TCM carries out a pre-handover snagging inspection internally before inviting the client to the formal handover walkthrough, so the list is typically short.
Related Services and Guides
Commercial Fit-Out Services
Full CAT A and CAT B fit-outs across Hertfordshire and North London
Office Fit-Out
Bespoke office fit-outs from survey to handover
Retail Shop Fit-Out
Retail fit-outs for Hertfordshire and North London businesses
Commercial Refurbishment
Refurbishment of occupied commercial premises
Commercial Fit-Out Cost Guide
CAT A and CAT B costs per sq ft in 2026
Commercial Maintenance
Ongoing maintenance contracts after your fit-out
Planning a Commercial Fit-Out?
TCM Building & Maintenance delivers commercial fit-outs across Hertfordshire and North London. Fixed-price contracts, IPAF certified, CDM compliant. Get a free survey and detailed programme.