Taking on bigger projects is the goal for most builders who’ve been grinding away as sole traders or small outfits. At some point, you simply can’t do it all yourself. More hands on site means more work completed, better programmes, and the ability to bid on contracts that were previously out of reach. But hiring subcontractors is not as simple as ringing a mate and telling him to show up Monday morning. There are legal obligations, tax responsibilities, and contract formalities that, if ignored, can land you in serious bother with HMRC and leave your business exposed when things go wrong. This guide covers the whole picture.
Why Hiring Subcontractors Makes Business Sense for Growing Builders
When you’re taking on extensions, refurbs, or new-build plots, you need specialist trades you can’t reasonably be across yourself. Plasterers, electricians, plumbers, groundworkers. Bringing these in as subcontractors keeps your fixed overhead down. You’re not carrying employees on your payroll through quiet periods, you’re not paying employer’s National Insurance, and you’re not locked into employment law obligations. That flexibility is the whole point.
According to the HMRC Construction Industry Scheme guidance, hundreds of thousands of subcontractors operate within the UK construction sector at any one time. The industry runs on this model. But the rules exist for a reason, and the builders who get caught out are usually the ones who thought paperwork was someone else’s problem.
How to Find Reliable Subcontractors
Word of mouth is still the best way. Ask other builders, your merchant contacts, or suppliers on site who they’ve used and rated. A plasterer who comes recommended by three people you trust is worth far more than a stranger off a general listing site.
That said, platforms like Checkatrade, Rated People, and local trade Facebook groups have become genuinely useful for finding trades in specific areas. Federation of Master Builders membership is another signal worth looking for. It doesn’t guarantee quality, but it does mean the person takes their trade seriously enough to maintain a professional standing.
When you’re first considering hiring subcontractors, build a shortlist of at least two or three options for each trade type. That way you’re not scrambling when your first-choice tiler is already booked out six weeks.
What to Check Before You Commit
Before anyone sets foot on your site, do a basic check. Ask for proof of Public Liability Insurance. A minimum of £1 million cover is standard; £2 million or more is better for anything other than small domestic jobs. Check it’s current, not last year’s certificate dug out of a drawer.
Ask for their UTR (Unique Taxpayer Reference) number. If they can’t provide one quickly, that’s a red flag. You’ll need it for the Construction Industry Scheme. Also check their CIS registration status via HMRC’s online verification service before making any payments.
For electrical and gas work, trade certification is a legal requirement. NICEIC or NAPIT for electricians, Gas Safe for anything involving gas. There’s no flexibility here. Engaging unregistered trades on notifiable work is a liability you don’t want near your business.
Understanding Your CIS Obligations as a Contractor
The Construction Industry Scheme is the part most small builders either don’t understand or conveniently forget about. If you’re hiring subcontractors to carry out construction work, and you yourself are paid under CIS by a client or main contractor, you are classed as both a subcontractor and a contractor. That means CIS obligations run in both directions.
As a contractor, you must register with HMRC as a contractor under CIS before your first payment to a subcontractor. Then, before paying any subcontractor for the first time, you verify them with HMRC. The result of that verification determines the deduction rate you apply:
- 20% deduction for registered subcontractors.
- 30% deduction for unregistered subcontractors.
- 0% (gross payment) for subcontractors who’ve qualified for gross payment status.
You deduct the relevant percentage from the labour portion of the payment only. Materials are excluded. You then pay that deduction to HMRC by the 19th of the following month and file a monthly CIS return showing what you’ve paid and deducted. Miss the deadline and fines start at £100. It escalates fast if you keep missing it.
Keeping a clear breakdown of labour versus materials on every subcontractor invoice is therefore not just good practice. It’s essential. Make sure your subs invoice correctly from day one.
Written Contracts: Don’t Skip This Step
A handshake and a price agreed on the phone is a dispute waiting to happen. When you’re hiring subcontractors for anything beyond a couple of days’ work, you need something in writing. It doesn’t need to be a 40-page legal document. A clear, one-page written agreement covering the key points will do the job.
At minimum, your subcontract should cover:
- Scope of works and specification reference
- Start date and expected programme
- Agreed price (fixed, day rate, or measured)
- Payment terms (more on this below)
- Variation procedure
- Insurance requirements
- Health and safety responsibilities on site
- Defects liability period
There are template subcontract agreements available through the Federation of Master Builders and the Joint Contracts Tribunal (JCT) for various sizes of project. Using one of these gives you a legally sound starting point without paying a solicitor every time.
Payment Terms and the Late Payment Problem
Cash flow is the thing that kills building businesses, and it flows directly from how you structure payment with both your clients and your subcontractors. The general principle is simple: don’t pay out more than you’ve been paid, and don’t pay before the work’s been properly checked.
Agree payment intervals upfront. Fortnightly or monthly applications work well on longer projects. Tie payments to completion of defined stages, not just to dates, so there’s a measurable trigger. Retain a small percentage (typically 2.5% to 5%) until the end of the defects liability period so you have some leverage if snags appear.
The Construction Act (Housing Grants, Construction and Regeneration Act 1996, as amended) gives subcontractors the right to suspend work for non-payment after giving seven days’ notice. Knowing this law works in both directions is useful. You’re protected by the same provisions when your client is the one dragging their heels.
Employment Status: The Self-Employed Test
One area where builders regularly come unstuck is treating workers as subcontractors when HMRC views them as employees. The distinction matters enormously. Get it wrong and you’re looking at backdated PAYE, employer’s NI, and potential penalties.
HMRC looks at a range of factors: does the person work for other clients? Do they bring their own tools? Can they send a substitute? Do they set their own hours? The more control you exercise over how and when someone works, the more they look like an employee. Someone who shows up every day, uses your tools, works solely for you, and follows your daily direction is almost certainly an employee in legal terms regardless of what the invoice says.
If you’re genuinely unsure, use HMRC’s Check Employment Status for Tax (CEST) tool before you start paying anyone. It’s not perfect, but it’s HMRC’s own guidance tool and gives you a documented position if questions arise later.
Running a tight building business means staying on top of the details. It’s a bit like how a well-designed mechanical system works, every part doing its specific job precisely. That same principle applies whether you’re building an extension in Swindon or, for that matter, whether you’re buying LEGO Technic for a kid who’s got a thing for engineering. Every component has its place and function.
Building the Right Team Over Time
The best subbies are the ones you work with repeatedly. Once you’ve found reliable trades who understand your standards and your way of working, hold onto them. Pay them on time, treat them professionally, and communicate clearly. The building industry runs on relationships, and a good network of trusted subcontractors is genuinely one of the most valuable assets a growing builder can have.
Hiring subcontractors for the first time feels like a jump. The paperwork seems daunting. But once the CIS process is set up, the contract templates are in place, and you’ve got two or three reliable trades you can call on, it becomes second nature. And it opens the door to projects you’d never have been able to touch on your own.
Frequently Asked Questions
Do I need to register for CIS before hiring my first subcontractor?
Yes. If you’re paying subcontractors for construction work, you must register as a contractor with HMRC under the Construction Industry Scheme before making any payments. You then verify each subcontractor through HMRC before paying them for the first time, which determines the correct deduction rate to apply.
What deduction rate do I apply to subcontractor payments under CIS?
It depends on the subcontractor’s registration status. Registered subcontractors have 20% deducted from the labour element of their payment. Unregistered subcontractors have 30% deducted. Those with gross payment status receive the full amount with no deduction. Always verify status through HMRC before the first payment.
What insurance should a subcontractor have before working on my site?
At minimum, subcontractors should hold current Public Liability Insurance, typically at least £1 million cover for domestic work and £2 million or more for commercial projects. Relevant trade certifications are also required for regulated work, such as Gas Safe registration for gas work and NICEIC or NAPIT registration for electrical installation.
Can I treat a worker as self-employed even if they work for me every day?
Not necessarily. HMRC assesses employment status based on actual working arrangements, not just what an invoice says. If someone works exclusively for you, uses your tools, follows your daily direction, and cannot send a substitute, HMRC may class them as an employee. Use HMRC’s CEST tool to check status and document your position before engaging anyone regularly.
Do I need a written contract with every subcontractor?
For any work beyond a day or two, a written agreement is strongly advisable. It protects both parties by clearly setting out scope, price, payment terms, and responsibilities. JCT and the Federation of Master Builders both offer template subcontract documents suited to different project sizes, making it straightforward to have something legally sound in place.
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