The moment a client walks around a finished job and starts writing things down on a piece of paper is one every tradesman recognises. That list, and the paperwork that goes with it, is where plenty of builders lose money they should have kept. Understanding what practical completion actually means, legally and practically, is not just useful knowledge. It protects your final payment.
I’ve seen builders hand over keys thinking the job was done, only to spend the next six months going back to fix things they weren’t even responsible for. It usually came down to one thing: they never got a practical completion certificate signed off properly, and they had no idea what the defects liability period was supposed to cover.
What practical completion actually means in UK law
Practical completion is not the same as the job being finished to perfection. In UK contract law, it means the works are complete in all material respects and the building can be used for its intended purpose. There might be minor outstanding items, but nothing that stops the client from moving in or using the space. That distinction matters enormously.
The leading case most construction solicitors point to is Jarvis v Westminster Corporation, but the practical interpretation has been refined through years of case law. The clearest explanation for most builders comes from the Joint Contracts Tribunal, whose standard building contracts are used on the majority of domestic and commercial projects across England and Wales. Under a JCT contract, practical completion is certified by the contract administrator, usually the architect or project manager, not the builder. That is an important point many tradesmen miss.
On a simple letter-of-agreement job with no formal contract administrator, practical completion is effectively what you and the client agree it to be. Which is exactly why getting something in writing at that stage is not optional.
What the practical completion certificate triggers
The certificate is not just a piece of paper. Its issue starts a clock running on several things that directly affect your money and your liability.
First, it releases the first half of any retention held. Under a standard JCT Minor Works contract, 3% to 5% of the contract value is typically held back, split between practical completion and the end of the defects liability period. If the certificate never gets issued properly, the client has a technical argument for holding on to that money indefinitely. I’ve spoken to builders who waited over a year for retention they were owed because nobody formalised practical completion at the time.
Second, it starts the defects liability period. This is typically six months under JCT Minor Works and twelve months under JCT Standard Building Contract, though it can be varied. During this period, the contractor remains responsible for returning to fix defects that appear, provided those defects stem from the original works and are not down to the client misusing or damaging things. The period ends with the issue of a Making Good Defects certificate, after which the second half of the retention should be released.
Third, risk in the building passes from contractor to employer. This has insurance implications. Once practical completion is certified, the client is responsible for insuring the structure.
Snagging lists and what they mean for final payment
A snagging list compiled at practical completion should document minor outstanding items, small defects, or finishing touches that do not prevent the building being used. Think a few doors that need adjusting, a patch of paintwork that needs touching up, or a tile that wants re-grouting. What it should not include are fundamental defects, incomplete sections of work, or things the client simply changed their mind about.
The problem in practice is that clients sometimes treat the snagging list as a negotiating tool. Every builder has had a client add items to a snag list that were never part of the contract, or declare that practical completion has not been reached because of a minor cosmetic issue. Knowing your contract position stops that tactic from working.
Under a JCT contract, the contract administrator must act independently and cannot simply refuse to issue the certificate because the client is unhappy. If you believe practical completion has been reached and the certificate is being unreasonably withheld, you have grounds to raise a dispute. Outside a formal JCT framework, the position is murkier, which is one more reason to have a written agreement, however basic, before you start any job.
On smaller domestic jobs I’d always recommend taking dated photographs of the finished work before handing over. Get the client to sign a simple completion statement, even if it’s just an email confirmation that they’re happy the works are done. That paper trail is worth its weight if things turn awkward later. If you want to keep your business watertight on cost too, there’s good reading in how to estimate labour hours without undercharging, because protecting your margin starts well before the snag list conversation.
Working under JCT vs a letter of agreement
Most builders on domestic extensions, loft conversions and smaller new builds are not working under a full JCT Standard Building Contract. They’re either using JCT Minor Works, a homeowner contract, or something written on headed paper by whoever hired them. Each situation changes how practical completion works in practice.
Under JCT Minor Works, the process is relatively straightforward. The contract administrator inspects, issues the certificate, and the retention clock starts. Under a letter of agreement, there is no contract administrator, so both parties need to agree in writing that the works are complete. Without that agreement documented, the builder is exposed to arguments about whether they’re still liable for defects years down the line.
If you’re doing work where cavity wall construction or structural elements are involved and building control is on site, the building control sign-off is sometimes confused with practical completion. They are completely separate. Building control sign-off confirms compliance with the Building Regulations. It says nothing about whether the contractual works are complete or what retention is now due.
Similarly, work that feeds into EPC ratings and retrofit compliance may require additional certification from assessors. That paperwork also sits outside practical completion, though clients sometimes make releasing final payment conditional on receiving it. If you’ve agreed to provide it, fine. If not, make sure your agreement is clear on what’s actually required before money changes hands.
Protecting yourself whether the contract is formal or not
The most practical thing any builder can do is treat practical completion as a formal milestone on every job, regardless of whether there’s a JCT contract in place. That means a written record of the date works are completed, a list of any agreed minor outstanding items and a realistic timescale for finishing them, and confirmation from the client that they accept the building for use.
If the client refuses to accept completion without good reason, document that refusal in writing. Send a letter or email stating that in your view the works are practically complete, listing any minor outstanding items you accept responsibility for, and noting the date. That creates a paper trail that matters if the dispute goes further.
On retention, always have it written into your agreement from the start. Never let a client invent a retention arrangement mid-job. Know what percentage is held, when it’s released, and what the defects liability period covers. The HMRC Construction Industry Scheme guidance on gov.uk is worth revisiting alongside this, because final payments also interact with CIS deductions in ways that trip people up.
Practical completion is one of those areas where the gap between what tradesmen think is happening and what the contract actually says can cost real money. Get it right, document it properly, and you spend your defects liability period fixing genuine snags rather than fighting about whether the job was ever done at all.
Frequently Asked Questions
Who issues a practical completion certificate on a UK building job?
Under a JCT contract, the certificate is issued by the contract administrator, who is usually the architect or project manager appointed by the client. On simpler domestic jobs without a formal contract administrator, practical completion is agreed between the builder and client, ideally confirmed in writing rather than just verbally.
What happens if a client refuses to sign off practical completion?
If a client refuses to certify practical completion without legitimate reason, the builder should document their position in writing, stating that works are complete and listing any accepted minor outstanding items. Under a JCT contract the contract administrator must act independently, so a refusal can be challenged. Outside formal contracts, keeping a dated paper trail is essential if the matter escalates.
How long is the defects liability period after practical completion?
Under JCT Minor Works it is typically six months. Under a JCT Standard Building Contract it is usually twelve months. The period can be negotiated, so always check what is stated in your specific contract. During this time you are responsible for returning to fix defects that arise from your own works.
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