For business owners, landlords and developers
What Does a Commercial Contractor Do? Full Guide
Sviatoslav JerdetchiiCEO & Founder of Craftex. Updated , 7 min read
The short answer
A commercial contractor builds, converts, refurbishes or fits out buildings used for business. They price the work, plan the programme, run the site and the trades, and carry the legal health and safety duties until handover.
- Before work starts: survey, price, programme and order the long-lead items.
- On site: manage every trade, safety, quality, neighbours and changes.
- By law: usually acts as principal contractor under CDM 2015.
- At the end: test, sign off, hand over and fix defects.
Most people only meet a commercial contractor when something has to be built by a date. A lease ends. A shop must open. A school needs its pool back for the new term. So what does a commercial contractor actually do between the first call and the keys?
This guide explains the job in plain English, stage by stage. It covers the legal roles, the main types of contractor and how the work looks on real projects. We're a London design and build contractor, so it's written from the builder's side. Have a building in mind? Book a site visit and we'll walk it with you.
What a commercial contractor does, in short
A commercial contractor delivers construction work for a business. That means offices, shops, restaurants, clinics, schools and warehouses. The work can be a new build, a conversion, a refurbishment or a fit-out.
The contractor takes your design and your budget and turns them into a finished building. They plan the work, hire and manage the trades and buy the materials. They control safety and quality on site. Then they test everything, hand it over and fix any defects.
On most projects the contractor is also the one legal point of control on site. That's the role the law calls principal contractor. More on that below.
The commercial contractor's job, stage by stage
The work starts long before anyone picks up a tool. This is how the job runs on a typical commercial fit-out or refurbishment.
| Stage | What the contractor does | What you get |
|---|---|---|
| Survey | Inspects the building, services, structure and access | A list of risks before you commit |
| Pricing | Prices the scope, line by line or as a lump sum | A written price against a clear scope |
| Programme | Plans the sequence and the long-lead items | Dates you can plan a move or opening around |
| Pre-construction | Finalises design details, orders materials, books trades | A site that starts ready, not waiting |
| Construction | Runs the site, the trades, safety and quality every day | Progress you can see and measure |
| Handover | Tests, commissions, cleans and signs off | A working building and its manuals |
| Aftercare | Returns to fix defects in the agreed period | Problems fixed without a fight |
Before work starts: survey, price and programme
The survey is where a good contractor earns its fee. Old buildings hide things. Floors are not level. Services are smaller than the drawings say. A price given before anyone has looked is a guess.
At The Gloucester Arms, a 300 m² London pub, we surveyed the fabric and services before construction. The strip-out was planned with a contingency for the defects old pubs hide. The refurbishment ran on a 10-week programme.
On site: trades, safety, quality and neighbours
Once work starts, the contractor runs the site every day. They sequence the trades so nobody waits for anybody. They keep the site safe, check the work and deal with neighbours, tenants and the building manager.
They also manage change. Every project has some. A good contractor prices a change before it is built, so you decide with the cost in front of you.
At the end: testing, sign-off and handover
The last fortnight is busy. Fire alarms, emergency lighting, ventilation and power are tested. Building control signs off the work. You receive the certificates, the manuals and a clean building.
The legal side: what CDM 2015 makes a contractor do
In the UK, most commercial projects fall under the Construction (Design and Management) Regulations 2015, known as CDM. They set out who is responsible for health and safety at each stage.
On a project with more than one contractor, the main contractor usually becomes the principal contractor. Their job is to plan, manage, monitor and coordinate health and safety during the construction phase. They also make sure workers are consulted about their own safety.
Since 1 October 2023, the Building Regulations add a similar duty in England. Where more than one contractor is involved, the client must appoint a principal designer and a principal contractor in writing. The client must also take reasonable steps to check they are competent.
Larger projects must be notified to HSE before the construction phase. A project is notifiable if it lasts more than 30 working days with more than 20 workers at once, or exceeds 500 person days. Our guide to CDM 2015 client duties on a fit-out explains what that means for you.
Five types of commercial contractor
Commercial construction isn't handled by one kind of firm. The right type depends on the size and scope of the job.
- General or main contractors. They coordinate the whole project: planning, programme, budget and every trade on site. They oversee the build from start to finish.
- Design and build contractors. One company takes on both the design and the construction under one contract. You deal with one team, and design and cost develop together.
- Fit-out contractors. They complete the inside of a building. A Cat A fit-out gives you a usable shell with ceilings, lighting and services. A Cat B fit-out adds the layout, finishes, furniture and technology.
- Specialist contractors. They focus on one system, such as electrics, ventilation, plumbing, fire protection or roofing. They usually work under the main contractor.
- Civil or structural contractors. They build foundations, frames, drainage and the structure itself.
Not sure which one you need? We compare two of them in fit-out contractor vs general contractor. Most mid-size jobs in London, from £100,000 to £10M+, suit a design and build contractor. That's where we work.
Fuse Energy hired Craftex on the fit-out and installation of our engineering and research centre, which included electrical, heating, lighting, plumbing, and ventilation upgrades. They delivered everything to a high standard and were proactive throughout — even working weekends to help speed up the programme, despite not being contracted to. They managed last-minute changes very well, communication was clear and consistent, and the team was professional from start to finish. We’d happily recommend Craftex to anyone needing a reliable construction partner.
What a commercial contractor does on real projects
Definitions only go so far. Here's what the job looked like on two of our projects, both with a fixed date and people using the building.
A school pool, ready for the new term
At Francis Holland School, we refurbished the swimming pool and its facilities. The area was 1,250 m², and the programme was 16 weeks. The new term was the deadline, and it could not move.
A pool is a hard place to build. Moisture, chemicals and heavy use punish the wrong materials. We managed every trade directly and sequenced the work around the school calendar. The facility was ready for pupils on the first day of term.
A live warehouse that never stopped
After an office project for the same client in Kensington, they hired us for their Banbury warehouse. The warehouse had to keep working. In four weeks we built 148 sq m of new space. It holds a changing room with lockers and a storage room with pallet racking and safety barriers.
Repeat work is the clearest sign a contractor did the first job well.
How a commercial contractor keeps a project on time and on budget
Most overruns start before the site opens. These are the habits that stop them.
- Survey first. Problems found before pricing cost far less than problems found during strip-out.
- Freeze the design early. Changes after work starts cost the most.
- Order long-lead items first. Bespoke joinery, glazing and equipment break more programmes than the trades do.
- Price every change before it is built. You keep control of the budget.
- Report weekly. Progress, risks and the decisions needed from you.
Material and labour prices still move during a project. We explain why in the rising cost of construction labour and materials. Our guide to delivering projects on time and on budget shows how we plan each stage.
What a good commercial contractor does that an average one doesn't
Good and average contractors use the same trades and materials. The difference is in how they run the job.
If you're comparing firms now, our guide to commercial construction companies in London lists the checks to make before you sign.
How Craftex works as your commercial contractor
Craftex started in 2016 as a carpentry and joinery company. Today we design and build commercial projects across London. Around 60% of our labour is in-house, so the joinery and finishes stay under our control.
We hold £10 million public liability and £10 million employers' liability cover. One team runs your project from survey and design to handover.
A contractor's job doesn't end with the build. Good design decisions also cut running costs, as we show in energy efficiency in data centre construction. And a layout that works starts with commercial space planning.
Have a project in mind? Book a site visit. We'll walk the building with you, flag the risks and give you a clear scope and price.
Seven traits of a good commercial contractor
- Clear communication with you, the designers and the site team.
- Sound knowledge of Building Regulations, fire safety and access.
- Calm problem-solving when supplies slip or the building surprises everyone.
- Careful control of the budget and the materials.
- A firm grip on health and safety, every day.
- Attention to detail, checked as the work goes, not just at the end.
- Honest, regular updates, including bad news early.
