Estimated read time: 7 minutes
When you’re planning a significant home improvement — a loft conversion, rear extension, or full refurbishment — one of the earliest decisions you’ll face is this: do you hire a main contractor to manage everything, or do you save money by appointing separate trades yourself?
It’s a question we get asked regularly at Excel Construction. And it’s a fair one. On the surface, going direct to individual tradespeople can look like a smart way to cut costs. You’re cutting out the “middleman”, right?
In this article, we’ll explain exactly what a main contractor does, what managing your own trades actually involves, and help you decide which approach is right for your project — and your budget.
What does a main contractor actually do?
A main contractor takes responsibility for the entire project. That means appointing, scheduling and coordinating all trades — groundworkers, structural engineers, bricklayers, carpenters, roofers, plumbers, electricians and plasterers — in the right sequence. Procuring materials, managing deliveries, and keeping the site clean, safe and compliant. Holding contracts with each trade, meaning you have one point of accountability if something goes wrong. Providing a fixed programme so you know when each phase starts and finishes. Carrying full insurance and, where applicable, operating under a JCT contract that protects both parties.
In short, a main contractor doesn’t just build — they manage risk on your behalf.
What does managing your own trades involve?
When you manage separate trades yourself, you become the project manager. That means finding and vetting each trade individually, coordinating their diaries so they arrive in the right order, chasing them when they don’t show up, making decisions on the spot when problems arise — and on a building site, problems always arise — and taking on the financial and legal risk if something goes wrong between trades.
Many homeowners underestimate how much time and expertise this requires. Construction projects have dependencies — one trade’s delay cascades into the next. Without someone experienced managing that sequence, costs and timescales spiral quickly.
What you don’t know can cost you
This is where the difference between a homeowner managing trades and an experienced main contractor becomes most apparent — and most expensive.
When we walk onto a site, 20 years of experience shapes where we look and what we see. We know which details to check on a plumber’s work, how a carpenter’s fixings should look, whether a bricklayer’s bed joints are consistent. We know the failure points that don’t show up until six months after completion — the product specified that won’t last, the joint that will let in water, the fixing that will work loose.
A homeowner managing their own trades doesn’t have that reference point. You can see whether a wall looks straight. You cannot easily see whether the materials used will perform over the next 20 years, or whether a detail has been cut that will cause a problem you won’t notice until the damage is done.
We regularly advise clients away from materials and products they’ve found online. The appeal is understandable — the price looks attractive and the product looks similar. But building work is not a purchase you replace in a few years. A roof, an extension, a structural frame — these need to perform for the next two decades at minimum. The saving on a cheaper product rarely survives contact with a repair bill five years later.
Part of what you are paying for with an experienced main contractor is the knowledge of what not to use, and the professional standing to push back when a cheaper option is being considered. That kind of advice is hard to put a number on — but it protects your investment.
A real example from South London
We were called to a project in Morden by a homeowner who had been managing their own trades for a loft conversion and rear extension. They had appointed different companies for different parts of the work and were coordinating everything themselves.
By the time we arrived to carry out the roof structure and loft shell — our specific scope — the site was in a poor state. Rubbish was everywhere. Materials were stored incorrectly, creating hazards. The screed on the extension floor was inconsistent in height and already cracking. The drainage and plumbing had been installed incorrectly.
Our contract was for the roof structure only — £48,000 of work — and we completed that to our usual standard. But the remedial work required on the extension was so extensive that we couldn’t take it on without essentially rebuilding it. The homeowner ultimately had to return to their bank and borrow additional money to get the project finished.
This isn’t an isolated case. We see variations of this story regularly. The intention to save money is understandable — but the cost of putting things right almost always exceeds what a main contractor would have charged in the first place.
Where self-managing can go wrong
Trades arriving out of sequence
If your plasterer arrives before your electrician has first-fixed, walls have to come down. If your screed goes down before drainage is signed off, you may be cutting it up again. Sequencing is everything on a building project, and it requires experience to get right.
No single point of accountability
When something goes wrong — and on any project of scale, something will — who is responsible? If three separate companies have touched the same area of work, each will point to the others. A main contractor absorbs that argument on your behalf.
Site safety and compliance
A construction site is a regulated environment. There are rules about waste disposal, material storage, welfare facilities, and working at height. When you manage your own trades, compliance responsibility falls on you as the client. A main contractor handles this as part of their role.
Programme overruns
Tradespeople are busy. Without a main contractor applying programme pressure, gaps appear between trades — days or weeks where nothing happens. A project that should take four months can easily stretch to eight.
When might managing your own trades make sense?
We believe in being straight with our clients. There are situations where self-managing can work. For very small, single-trade jobs — a bathroom refurbishment with one plumber, for instance — there’s no coordination challenge. If you have a construction background yourself and understand sequencing, procurement and site management, you may be well placed to manage certain projects.
But for any project involving structural work, multiple trades, or a programme longer than a few weeks, the risk of self-managing almost always outweighs the saving.
What does a main contractor cost?
Main contractors typically charge a management margin on top of trade and material costs — usually somewhere between 15% and 25%, depending on project complexity and size. This covers their programme management, site supervision, procurement, insurance, and the risk they carry on your behalf.
On a £200,000 project, that might represent £30,000–£40,000. It sounds significant. But when you consider that a single sequencing error — a floor screed laid before drainage sign-off, or a roof structure built over incorrect wall heights — can cost more than that to put right, the maths changes considerably.
Our approach at Excel Construction
We operate as a main contractor on every project we take on. That means you have one contract, one programme, and one point of contact. We have a setting-out engineer on every project, our own directly employed teams, and over 20 years of experience delivering high-specification residential work across South London, Croydon and Surrey.
We also believe that the client should always be informed and involved. On older properties especially — where we might discover joist levels aren’t straight, or party walls aren’t where the drawings suggest — we come back to you with options and recommendations. It’s your project and your home. Our job is to give you the information you need to make good decisions, and then deliver on whatever we agree together.
If you’re weighing up your options for an upcoming project, we’re happy to talk it through. Get in touch with the Excel Construction team here.