A straight-talking guide from Excel Construction based on 20 years of delivering high-specification projects across South London, Croydon, and Surrey.
Hiring a contractor for a significant home project is one of the largest financial decisions most people will ever make. And yet the process most homeowners follow get three quotes, pick the middle one, hope for the best leaves them dangerously exposed.
We have been called in to fix other contractors’ work more times than we care to count. Structural problems. Abandoned sites. Contracts that offered no protection whatsoever. In almost every case, the root cause was one of the seven mistakes below.
Read this before you appoint anyone.
Mistake 1: Hiring a Contractor Who Isn’t the Right Size for Your Project
Most homeowners focus on price. Very few think about capacity or compliance.
A contractor turning over £400,000 a year typically runs one or two teams. They have limited insurance, limited reserves, and limited ability to absorb problems. If your project hits an unexpected complication bad weather, a supplier failure, a structural issue they have nothing to draw on. Their entire operation is your job.
The same applies at £1 million turnover. One significant problem on one project can destabilise the whole business.
Excel Construction turns over £5 million a year. At any given time we are running ten projects simultaneously across South London and Surrey with ten directly employed teams. If something needs to move a team reassigned, a programme adjusted, a specialist brought in at short notice we have the capacity to do it without your project suffering.
Compliance is not optional and it changes constantly
Building regulations, planning requirements, party wall legislation, health and safety law these are not static. They update regularly, and a contractor who is not actively investing in staying current is a contractor who is cutting corners without necessarily knowing it.
We invest continuously in compliance. Our team holds current accreditations, we stay ahead of regulatory changes, and we carry full public liability, employers’ liability, and contract works insurance commensurate with the scale of work we deliver.
We also invest in systems that give clients genuine peace of mind
Every client gets their own portal on Buildertrend our project management platform updated daily with progress photographs, programme tracking, and cost reporting. You can see exactly what is happening on your project at any time, from anywhere. No chasing. No waiting for a call back. Full transparency from day one to handover.
A £400,000 contractor running jobs off a WhatsApp group is not the same operation. Twenty years in business means we have seen everything and we are still here, which is more than can be said for contractors who were not built to last.
When you are spending £100,000 to £500,000 on your home, the contractor’s turnover, capacity, compliance record, and systems matter as much as their price.
Mistake 2: Signing a Contract That Isn’t Linked to the Full Project Package
Most homeowners think a contract is just a piece of paper with a price on it. It isn’t or it shouldn’t be.
A properly constructed contract is a complete package. When Excel Construction submits a contract for signature, it is linked to and supported by every relevant document: the architectural drawings, the structural engineer’s calculations, the party wall award (where applicable), the full specification, the insurance certificates, and the payment schedule.
By the time a client signs with us, there should be no ambiguity whatsoever about what is being built, to what standard, under what conditions, and at what cost. Every question should already be answered on paper.
The payment schedule is not a separate conversation to have after the contract is signed. It is part of the contract. It should be agreed, documented, and signed at the same time as every other element of the project package. If a contractor presents you with a contract and tells you the payment schedule will be sorted out later, that is not acceptable. It should already be there.
The payment schedule
Our payment milestones are tied directly to construction progress not to dates on a calendar. You pay when a defined stage of work has been completed and verified. Not before. This protects you from paying for work that hasn’t happened, and it protects us from cash flow problems caused by late payment.
The final payment is released only when snagging is complete and the completion certificate is in place. Not before. The contractor’s incentive to finish properly is built into the structure of the contract.
What the JCT contract actually does
The JCT the standard form of building contract used by professional contractors across the UK is designed to protect both parties equally. It is not a tool for the contractor to hide behind. It gives the client clear rights and clear remedies. It gives the contractor clear obligations and clear protections against scope changes, unreasonable demands, and late payment.
A contractor who uses a one-page letter, a simple email, or no written agreement at all is not protecting you. They are also not protecting themselves which tells you something about how seriously they take the project.
Ask to see the full contract package before you sign anything. If it doesn’t include the drawings, the specification, the engineer’s calculations, and a milestone-based payment schedule it isn’t complete.
Mistake 3: Starting Without Complete Drawings and a Full Specification
Incomplete drawings are a recipe for disputes. We have seen it more times than we can count and it always costs the client more money, more time, and more stress than getting it right at the outset would have.
A set of basic architectural drawings tells you what is being built. It does not tell you how it is being built, or to what standard. Without a full specification alongside those drawings, every contractor will make their own assumptions and those assumptions will differ. That is why three quotes on the same basic drawings can vary by tens of thousands of pounds. The contractors are not pricing the same job.
The interior design problem
We once took on a project where the client provided basic drawings at the outset. Midway through the build, they appointed an interior designer and the specification changed dramatically. Over 100 additional electrical points were added beyond the original plan. Pendant lighting became shadow gap lighting. Standard tiling became a complex layout requiring a completely different approach.
None of this was in the original contract. All of it became a dispute.
The cost difference between finishing a room to a basic standard and finishing it to a high specification is significant and it is entirely in the detail. Consider the difference between:
A 600×600 tile and a 50×200 tile the smaller format requires far more cuts, far more time, and a completely different adhesive approach
A standard pendant light fitting and a shadow gap or cove lighting detail one is a standard electrical connection, the other requires precise joinery, plastering, and electrical coordination
A standard door with skirting and architrave and a hidden door with no visible frame, no skirting break, and no architrave — the latter requires bespoke joinery and precise sequencing across multiple trades
These are not finishing touches. They are construction decisions that affect programme, cost, and the sequencing of every trade on site. They need to be agreed before the contract is signed not discovered halfway through the build.
What you should have in place before signing anything
Architect’s drawings full planning and construction issue set
Structural engineer’s calculations
A complete interior specification finishes, tiles, sanitaryware, lighting design, joinery details
All client-supplied items confirmed and lead times checked
Party wall award if required
A contractor who is willing to start without these documents is a contractor who is planning to price the unknowns as variations once you are committed and have nowhere else to go.
Mistake 4: Assuming Building Control Is Someone Else’s Problem
Building control is not a formality. It is not a box to tick. And it is certainly not something you can skip and sort out later.
We were called by a friend who could not sell his house. The reason: no building control sign-off on works that had been completed years earlier. What followed was a rectification process additional work required to bring the property up to the standard that should have been met the first time before the sale could proceed. The cost, the delay, and the stress were entirely avoidable.
What building control actually involves
Building control inspectors visit at key stages of the project and issue a report after each visit. That report identifies outstanding items that need to be rectified, flags any discrepancies between the work on site and the approved drawings, and records any disagreements between the inspector and the design team.
We once had a building control inspector delay sign-off because he disagreed with our structural engineer’s calculations. This was not a failure of workmanship. It was a professional disagreement between two qualified engineers and it required careful, experienced liaison to resolve. That is not something a homeowner managing their own build is equipped to handle.
Construction is unpredictable. Experience is what manages that.
Anyone who thinks a contractor’s job is simply to build what is on the drawings is not understanding what construction actually involves. A contractor on a live site is constantly liaising with architects, structural engineers, building control, party wall surveyors, utility companies, and neighbours. When something unexpected happens and it always does — it is the contractor’s experience that determines whether it becomes a minor delay or a major crisis.
On a project in Brockley, we opened up a party wall and discovered it was single brick. We had never encountered that before on a property of that type. The structural steel beam we were about to install was specified to bear on a double-skin wall. It wasn’t there.
We stopped work immediately.
The client had to appoint a new structural engineer to redesign the connection detail. New drawings were produced. Building control was re-consulted. The programme was extended. None of this was anyone’s fault but it required immediate, experienced decision-making to prevent a dangerous situation from becoming a catastrophic one.
A less experienced contractor might have pressed on. We did not.
Mistake 5: Underestimating What a Complex Project Actually Requires
The bigger the project, the more moving parts. And the more moving parts, the greater the gap between a contractor who can manage them and one who cannot.
Planning drawings are a starting point. They are not a guarantee that what is drawn can be built exactly as shown. On larger or more complex projects conversions, multi-unit developments, mixed-use buildings the gap between what is approved on paper and what is deliverable on site can be significant. Managing that gap is the contractor’s job.
A real example: commercial to residential conversion in South London
We recently delivered a project converting a first-floor flat above a commercial unit into three new residential flats, with a new double-storey rear extension. The planning drawings were approved. The design team was in place. On paper, the project was straightforward.
It was not straightforward.
During the build, the fire brigade was consulted as required and identified a mandatory requirement for AOV (Automatic Opening Vent) Velux smoke ventilation windows that had not been specified in the original drawings. This was not optional. It was a statutory fire safety requirement, and without it the building could not be signed off.
What followed required simultaneous liaison with the architect, the structural engineer, and building control to redesign the affected areas, produce revised drawings, obtain updated approvals, and integrate the new specification into a build that was already underway.
We managed it. The building was signed off successfully. The client took possession on programme.
What larger projects actually require
On any project of significant scale or complexity, the contractor is not just a builder. They are the central coordination point for every professional involved architect, structural engineer, building control, fire brigade, party wall surveyor, utility companies, and specialist subcontractors.
When one of those parties raises a concern, changes a requirement, or identifies something that was not on the original drawings, the contractor needs to respond immediately, intelligently, and without panic. That requires 20 years of experience, established relationships with the professional teams involved, and a business with the capacity to absorb the unexpected.
The hidden cost of hiring the wrong contractor
Consider the hidden cost to the client on that project. The building owner is a solicitor. His time is billed at a premium hourly rate. If he had appointed a contractor who simply followed the drawings and left every coordination problem for the client to resolve — as many contractors do — he would have spent hours of his own highly paid professional time managing fire brigade consultations, chasing revised drawings, and coordinating between the architect and building control. That is not what he hired a contractor for.
The job description of a builder, in the narrowest sense, is to follow the plans. But the job description of a main contractor is to manage everything that happens when the plans meet reality. Those are two very different things — and the difference in cost between them is nothing compared to the cost of your own time, your own stress, and the delays that follow when no one is taking responsibility.
Mistake 6: Agreeing a Payment Schedule That Doesn’t Protect You
Most disputes between homeowners and contractors come down to money specifically, who has it and when.
A contractor who asks for a large upfront payment before work has started is a contractor who is using your money to fund their business. Established contractors with healthy cash flow, good supplier relationships, and a properly run operation do not need 30, 40, or 50 per cent of the contract value before a single block is laid. If they are asking for it, ask yourself why.
The right way to structure payments
Payment schedules should be tied to construction milestones not to dates, not to the contractor’s cash flow needs, and not to how persuasive they are in the initial meeting. The payment schedule must be agreed and signed as part of the contract not discussed afterwards.
A milestone-based schedule works like this: a defined stage of work is completed and verified, and payment is released for that stage. Foundations complete payment released. Superstructure complete payment released. Roof watertight payment released. And so on through to practical completion.
This protects you because you are never significantly ahead of the contractor. You are paying for work that has been done, not work that is promised. It also protects the contractor a fair payment schedule means we are not financing your project from our own reserves. It keeps the relationship clean and the project moving.
The final payment
The final payment should always be held until snagging is complete and the completion certificate is in place. This is non-negotiable. It is the contractor’s incentive to finish properly every last detail, every outstanding item on the snagging list rather than moving on to the next job and leaving yours 95 per cent done.
A contractor who pushes back on retaining the final payment until completion is telling you something about how confident they are in their own finish.
What to watch for
Any request for more than 10 to 15 per cent upfront before work begins
Payment tied to dates rather than completed stages
Pressure to release payments before a stage is visibly complete
No written payment schedule included in the contract
Mistake 7: Thinking You Can Manage the Trades Yourself
Every year, homeowners decide to save money by appointing trades directly a groundworker, then a bricklayer, then a carpenter, then a plumber, then an electrician and managing the project themselves. It is almost never cheaper. And it is almost always more stressful than they anticipated.
Trades do their bit. Nothing more.
An electrician is there to do electrical work. If something adjacent to his work needs doing — a small piece of boarding, a bracket fixed, a void made good he will not do it. That is not his job. The same applies to the plumber, the carpenter, the tiler. Each trade works within their own defined scope, and the gaps between those scopes and there are always gaps fall to whoever is managing the project. If that person is you, those gaps are your problem.
Coordination is a full-time job
A main contractor’s day is spent coordinating. Which trade is on site today. Which materials need to be there when they arrive. Which stage needs to be complete before the next trade can start. What happens when a delivery is late, a trade is sick, or a measurement turns out to be wrong.
When you manage trades yourself, you become that coordinator. You need to speak the language of every trade on site to know how long it takes to fit an oil radiator, hang a door, tile a square metre, rough-in a bathroom. If you do not know these things, trades will tell you what suits them not what is accurate.
Materials and time
A main contractor has trade accounts, material discounts, and established supplier relationships. We can predict lead times, order in advance, and keep a project moving because we know exactly what is coming and when.
A trade operative who runs out of materials will leave site to buy them. Then they are in traffic. Then they are back. Half a day is gone. On a project with multiple trades running simultaneously, this happens constantly and every hour lost costs money.
Compliance does not manage itself
We have changed glazing on a project because the specified glass did not meet current fire regulations. We have redesigned a roof detail because the original specification did not comply with building control requirements. These are not unusual occurrences they are the reality of construction on live projects with evolving compliance requirements.
A main contractor catches these issues, resolves them, and keeps the project moving. A homeowner managing their own trades discovers them when building control refuses to sign off or when something goes wrong.
The honest calculation
The saving you think you are making by managing trades yourself is consumed and then some by delays, rework, compliance issues, and the sheer volume of time you will spend on something you were not trained to do. Your time has a value. Your stress has a cost. And the mistakes made by uncoordinated trades on an unmanaged site have a price that is almost always higher than the main contractor’s fee you were trying to avoid.
A main contractor does not just build. They predict, coordinate, problem-solve, and take responsibility. That is what you are paying for and it is worth every penny.
The Question You Should Ask Every Contractor
Before you appoint anyone, ask them this: can you show me three completed projects of similar scale and specification, with contact details for the clients?
A contractor with nothing to hide will answer immediately. A contractor who hesitates, deflects, or offers you a portfolio of photographs instead of real references is telling you something important.
Get a Detailed Quote from Excel Construction
We are a fully insured main contractor with over 20 years of experience delivering high-specification residential projects across South London, Croydon, and Surrey. We use JCT contracts, we manage building control, we invest in compliance, and we give every client a fully itemised quotation and a milestone-based payment schedule before anything is agreed.
We are not always the cheapest quote. We are the contractor you will not need to call someone else to fix.
To request a site visit and detailed quotation:
Excel Construction Ltd
148 Addiscombe Road, Croydon
www.excelconstructionuk.co.uk
Published by Excel Construction Ltd. Based on 20 years of experience delivering residential construction projects across South London and Surrey.