Many homeowners assume the “10-year rule” can make an old, unapproved extension lawful, but this is one of the most commonly misunderstood areas of planning law.
In 2025, the rules around time-based immunity are clear:
The 10-year rule does not apply to home extensions depending on your situation, read on for the full breakdown…
Extensions fall under the 4-year rule, which covers most forms of unauthorised building works.
This guide explains the difference, how the rules apply in practice, when time-based immunity does not apply, and what homeowners need to understand before relying on it.
Contents
- The 4-year rule for operational development
- Did enforcement rules change in 2025?
- When the 4-year rule does not make an extension lawful
- How to prove an extension is lawful after 4 years
- Common misunderstandings about the 10-year rule
- Should you rely on time-based planning rules?
What is the 10-year rule?
The “10-year rule” is a planning law principle that makes certain unauthorised uses of land or buildings lawful once they have continued for 10 years without enforcement action.
What the 10-year rule applies to
The 10-year rule covers:
- Unauthorised changes of use (e.g., using a residential unit for long-term business use)
- Breaches of planning conditions (e.g., ignoring occupancy restrictions)
- Long-term use of land in a manner not covered by previous planning permissions
Why the 10-year rule does not cover extensions
Home extensions are categorised as operational development and physical building works, which fall under separate legislation.
For this reason, the 10-year rule cannot make an unauthorised extension lawful.
The 4-year rule for operational development
What the 4-year rule covers
The 4-year rule applies to:
- Single-storey extensions
- Two-storey extensions
- Loft conversions involving structural changes
- Outbuildings, annexes and garden rooms
- Garage conversions involving operational development
When an extension becomes lawful
An unauthorised extension may become lawful after 4 years if:
- The building work was substantially completed
- It has been in continuous residential use
- The council has taken no enforcement action within the 4-year period
After this, enforcement is no longer legally possible.
Why understanding the 4-year rule matters
Relying on the rule can:
- Affect your property’s value
- Influence mortgage and remortgage processes
- Impact future sales
- Introduce legal risk if evidence is weak
The rule is designed as protection, not as a shortcut around planning.
Did enforcement rules change in 2025?
Planning enforcement rules have been under review, with proposals to shift everything to a uniform 10-year enforcement period.
Current position (2025)
As of 2025:
- The 4-year rule still applies to domestic extensions
- The 10-year rule remains limited to use changes and planning condition breaches
Why this matters for homeowners
If changes occur in coming years:
- Historic unauthorised works may lose protection
- Evidence requirements may become stricter
- Councils may increase enforcement activity
Architectural input early on remains the safest approach.
When the 4-year rule does not make an extension lawful
While the 4-year rule can protect certain unauthorised extensions, it is not absolute. Even older extensions may still be unlawful if any of the following circumstances apply. Understanding these limitations is essential before relying on time-based immunity.
Enforcement was started at any point
If the council has taken any form of enforcement action within the four-year period, the extension cannot become lawful, even if the work has since stood untouched for many years.
What counts as enforcement?
- Formal enforcement notices
- Planning Contravention Notices (PCNs)
- Warning letters
- Requests for information about building works
- Documented site visits
Example:
If the council wrote to a homeowner in 2021 querying an unauthorised extension built in 2019, the enforcement investigation interrupts the 4-year period. Even if the investigation stalled without a formal notice, the 4-year rule cannot then be used to regularise the extension.
The extension was not fully completed
The 4-year clock begins only when the extension is substantially complete, meaning usable, watertight, and structurally finished.
Part-built works do not qualify.
Common misunderstandings:
- A shell without windows is not complete.
- A roof added years later resets the timeline.
- If internal work (e.g., adding a bathroom or heating) changes how the space is used, this may count as later completion.
Example:
A homeowner builds a rear extension structure in 2018 but does not install doors and finishes until 2020. The law considers completion in 2020, not 2018, so the extension will not qualify for the 4-year rule until 2024.
The extension has been altered before the 4-year period passed
Any material alteration, whether structural or affecting use, resets the 4-year clock.
Small repairs usually do not count, but changes that modify the form, size or function of the extension will.
Alterations that reset the clock:
- Adding an extra room or dividing walls
- Increasing the height or footprint
- Changing the roof form (e.g., flat to pitched)
- Converting the extension to a separate dwelling
- Adding new openings that change privacy or appearance
Example:
A rear extension built in 2017 has a new roof added in 2019. Because the roof is a material element of the structure, the “completion date” becomes 2019.
The property is a listed building
Listed buildings do not benefit from the 4-year rule. All works, even minor alterations, require Listed Building Consent, and unauthorised works remain unlawful indefinitely.
Important notes:
- Even internal works may require consent.
- Councils can prosecute owners for unauthorised work, even years later.
- Selling a listed property with unlawful extensions can be complicated and costly.
Example:
A small rear extension added to a Grade II listed cottage in 2010 without consent remains unlawful in 2025. Time does not make it legal.
Conservation area complications
While conservation areas still technically fall under the 4-year rule, councils often scrutinise evidence far more closely. Extensions that affect the character of the area may attract enforcement even many years later.
Common issues:
- Use of inappropriate materials
- Harmful changes to street-facing elevations
- Large extensions visible from public viewpoints
Example:
A homeowner in a conservation area adds cladding to a 2016 extension. In 2023, during a neighbour’s application review, the conservation officer raised concerns. The homeowner must now prove both the extension and the cladding were lawful at their respective dates, often a complex task.
Restrictive covenants or legal agreements
Even if an extension qualifies under planning’s 4-year rule, other legal restrictions can override time-based immunity. These may include:
- Restrictive covenants in property deeds
- Section 106 agreements
- Estate management schemes
- Rights of light or party wall implications
- Leasehold conditions
These operate independently of planning law.
Example:
A homeowner builds a side extension on land governed by a 1980s covenant prohibiting building within 1m of the boundary. The council may no longer enforce planning, but the covenant holder (often a developer or management company) can still demand removal.
How to prove an extension is lawful after 4 years
If an extension was built without planning permission, it does not automatically become lawful simply because four years have passed. To formalise its status and protect the property from future enforcement, homeowners must apply for a Certificate of Lawful Development (LDC). This certificate is the only official confirmation that the council recognises the extension as lawful.
Unlike a planning application, an LDC is based entirely on evidence, not opinion or design. The burden of proof lies solely with the homeowner.
Evidence the council will expect
Local authorities typically require multiple, consistent forms of evidence to demonstrate that an extension:
- Was substantially completed more than 4 years ago, and
- Has been in continuous residential use since then.
Because the council cannot rely on assumptions, they look for clear, date-stamped proof such as:
Dated photographs
Photographs showing the extension completed on a specific date, often sourced from:
- Time-stamped digital files
- Previous estate agent listings
- Google Earth historical imagery
- Family photos where the extension is visible
Example:
A holiday photo taken in June 2019 showing the completed extension can be strong evidence of the build date.
Builder’s documentation
Invoices, receipts, contracts or emails from contractors can help show when construction took place and when the works finished.
Example:
A final invoice marked “build completed October 2018” is usually strong evidence.
Statutory declarations (Sworn Statements)
Signed, legally binding statements from neighbours, the previous owner, or contractors confirming dates of completion.
Why they matter:
If photographic evidence is limited, statutory declarations can fill gaps, but they must be precise and credible.
Insurance and legal documents
Some home insurance policies, warranties or surveys reference the extension.
Example:
A 2019 homebuyer survey describing the extension demonstrates it existed at that point.
Land registry or local searches
Older title plans or search documents that refer to the extension can help establish its age and footprint.
Utility bills (in some cases)
If an extension contains a kitchen, bathroom or heated room, utility usage patterns may support the case that the space has been in continuous residential use.
Why strong evidence matters
Councils will only issue an LDC if they are satisfied on the balance of probabilities that the extension is over four years old and has remained in use. Weak or inconsistent evidence can create doubt, and in planning enforcement, doubt is enough for refusal.
Consequences of insufficient evidence:
Refusal of the LDC
Without a certificate, the extension remains technically unlawful, regardless of age.
Potential enforcement action
If the council believes the extension may have been built recently or altered within the last four years, they may open an investigation.
Delays or complications when selling the property
Buyers, solicitors and lenders almost always request proof of planning compliance.
Without an LDC, a sale can:
- fall through,
- be delayed, or
- require costly indemnity insurance.
Problems with remortgaging
Many lenders require extensions to have either planning permission or an LDC. If you cannot prove lawfulness, a remortgage may be declined.
Time passing is not enough, you must be able to prove the extension is older than 4 years.
Councils do not take homeowners’ word for it; everything must be evidenced.
Common misunderstandings about the 10-year rule
“My extension has been here 10 years, so it’s automatically legal.”
This is one of the most common misconceptions. Even if an extension has stood for a decade or more, it does not become lawful under the 10-year rule because physical building work is governed by the 4-year rule.
Example:
If a homeowner built a rear extension in 2014 without planning permission and never applied for a Lawful Development Certificate, the extension is not automatically lawful. The council may still refuse to issue a certificate if the homeowner cannot prove exactly when the work was completed, or if enforcement was initiated at any point, even informally.
A neighbour raising a concern in 2016, a site photo held by the council, or evidence the extension was modified in 2018 could invalidate any claim under the 4-year rule. Time alone is not enough; the burden of proof lies entirely with the homeowner.
“If no one complained, it must be lawful.”
Many homeowners assume a lack of objection means the council has accepted the extension. Unfortunately, that isn’t how planning law works.
Councils are not required to take enforcement action just because a breach exists. In fact, some breaches remain unnoticed for years, but without legal proof of completion, they are still considered unlawful.
Example:
A semi-detached homeowner builds a 5m rear extension without permission. None of the neighbours complain, and the council never inspects the property. Later, when the homeowner applies for a Lawful Development Certificate, they struggle to provide evidence showing the extension was completed more than four years ago. The council can refuse the certificate, making the extension unlawful even though no one ever objected.
“Estate agents said it’s fine.”
Estate agents may comment on how common extensions are in the area, or say a property “shouldn’t have an issue”, but this is not legal advice. Only the local authority can confirm the planning status of a structure.
Example:
A homeowner purchases a property with a side extension built 12 years earlier. The estate agent assures them “it’s been there ages, don’t worry.” Later, when the new owner tries to remortgage, the lender requests a Lawful Development Certificate. Because the previous owner never applied and cannot provide construction evidence, the council refuses. The buyer is left with an unlawful extension and complications with their lender, despite the agent’s reassurance.
“The council doesn’t check back gardens.”
While councils do not routinely inspect private gardens, they do respond to complaints, satellite imagery, and enforcement triggers. Modern planning enforcement increasingly uses aerial maps, street-view history, and historic photography.
Example:
A homeowner builds a 30sqm outbuilding without planning permission and assumes it will never be noticed because it sits behind tall fencing. Years later, a neighbour submits plans for their own extension. During the officer’s site assessment, the outbuilding becomes visible in aerial photography attached to the case notes. The council then opens an enforcement investigation into the unauthorised structure, even though the original owner thought it would remain unseen.
Even older breaches can be acted upon if their lawful status cannot be proven.
Should you rely on time-based planning rules?
Time-based planning rules can seem reassuring at first glance, a quiet sense that time will simply take care of things. But when it comes to your home, and the space you’re shaping for the future, relying on these rules alone can leave you exposed. They were never designed to replace planning permission, and they don’t offer the certainty most homeowners need when making decisions that shape how they live.
Why relying on the rules can be risky
Time-based rules offer protection in only a very narrow set of circumstances. They come with conditions, thresholds and responsibilities that sit firmly with you as the homeowner.
They can be risky because they:
- Do not replace formal planning permission
Time-based immunity is a retrospective safety net, not a green light. It does not guarantee approval and should not be treated as permission to build. - Can complicate the sale or remortgage of your home
Buyers, lenders and solicitors all look for certainty. Without formal approval in place, your project may raise questions at the moment you most need clarity. - Depend on strong, consistent evidence
The four-year rule isn’t about carrying on unnoticed. It hinges on proof — the kind that stands up to scrutiny and leaves no gaps. - May be reshaped by future planning legislation
Planning policy evolves. Proposals to change enforcement periods have already been discussed nationally. Relying on a rule that might shift beneath you carries its own risks.
Time passing is never the whole story. Certainty comes from transparency, from knowing the space you’ve created is recognised and supported by the right permissions.
The safer approach
For most homeowners, the safest and smoothest route is still the simplest one - secure planning permission or confirm your permitted development rights before you begin.
This gives you:
- A clear, lasting record of approval
- Confidence to make decisions about your home’s future
- Space to design more freely and more creatively
- Peace of mind when it comes to selling, remortgaging or extending further
It’s a foundation of certainty, the kind that lets you imagine what’s possible without looking over your shoulder.
Need clarity on your extension?
Whether you’re planning new works or trying to understand the status of an existing extension, professional guidance can help you avoid costly assumptions. A design-led architectural approach will ensure your project complies fully with planning, building regulations, and local policy.
