Extension Built Without Planning Permission 20 Years Ago? What Now?
13, Aug, 2026
A home without any paperwork can be a worrying sign for anyone. Many questions can come to mind, such as whether the council will take action, whether it will affect a future sale, or if you need to remove the extension. If the extension was built around 20 years ago, its age matters. However, you still need to check when it was completed, what approvals exist, and what evidence you have.
Does a 20-Year-Old Extension Still Need Planning Permission?
For an extension built around 20 years ago in England, the situation is different from a recent unauthorised extension.
For operational development completed before 25 April 2024, the planning enforcement period was four years. If the relevant conditions are met, the development may have become immune from enforcement after this period.
The rules changed on 25 April 2024, when a 10-year period became the standard for newer operational development. There are exceptions, including cases involving deliberate concealment or previous enforcement action.
So, an extension built 20 years ago is not automatically a problem. The key issue is proving when it was completed and checking its planning history.
What If You Cannot Prove When the Extension Was Built?
This is where homeowners face the biggest challenge.
Simply saying the extension has been there for 20 years is not enough. If you need to establish its planning status, you need evidence showing when the work was completed.
Useful evidence includes:
Dated photographs showing the extension.
Old property documents.
Invoices for construction work.
Utility bills.
Historic plans.
Council records.
Statements from people with direct knowledge of the work.
Government guidance on lawful development certificates also stresses the importance of evidence when establishing the age of development.
Start gathering your documents before making any application. Strong evidence gives you a clearer position and reduces uncertainty.
Should You Apply for a Lawful Development Certificate?
If an old extension appears to have become lawful through the passage of time, a Lawful Development Certificate, called an LDC, provides formal confirmation of its planning status.
This is different from retrospective planning permission.
An LDC asks whether the existing development is lawful based on the facts and evidence. Retrospective planning permission asks the council to assess an existing development as a planning application.
A certificate is not always required, but it is worth discussing with a planning professional if you are selling the property, planning more building work, or want formal evidence of the extension's status. Local planning authorities also recognise an LDC as useful documentation when questions about an old extension arise during a property sale.
You can read more about the process through the official Lawful Development Certificate guidance.
What About Building Regulations?
Planning permission and building regulations are separate matters.
An extension might have a planning history but no building regulations certificate. It might also have been built without either approval.
Building regulations cover areas such as:
Structural safety.
Insulation.
Fire safety.
Ventilation.
Drainage.
Electrical work.
If building work was completed without the required building regulations approval, a regularisation application provides a route for dealing with existing work. The council or building control body will assess the work against the relevant requirements.
Could an Old Extension Affect Selling Your House?
An old extension does not automatically prevent a property sale. However, missing paperwork can lead to questions from buyers, solicitors, or mortgage lenders.
You might be asked:
When was the extension built?
Was planning permission required?
Was building regulations approval obtained?
Is there evidence proving the age of the extension?
Is there a Lawful Development Certificate?
Does the extension match the existing property records?
Having clear documentation before putting your property on the market often makes the process easier.
Can You Extend a House With an Old Unauthorised Extension?
An old extension does not automatically prevent further building work.
However, the existing extension should be assessed before you design the next project. Your planning position, the property's history, the proposed work, structural condition, and local restrictions all matter.
For example, a homeowner might want to replace an old rear extension with a larger one. Another might want to add a loft conversion above a property with an existing rear addition. Each project needs its own planning and design assessment.
What Should You Do Before Starting More Work?
If you have an old extension with missing planning paperwork, follow these steps:
Find out when the extension was built.
Search the local council's planning records.
Check building regulations records.
Collect documents showing the extension's age.
Review whether a Lawful Development Certificate is appropriate.
Get professional planning and building advice before starting new work.
The Planning Portal also provides official guidance on planning applications, permitted development, and certificates.
Need Help Assessing an Old Extension?
Denham Crescent provides planning, architectural, extension, and renovation services across South West London. The team manages projects from feasibility and permits through design and construction, with one team overseeing the wider process.
Denham also holds TrustMark partnership status and highlights its experience with Wimbledon and surrounding South London properties.
Explore Denham's House Extensions service or Planning Permission service before planning your next project.
FAQs
Could a 20-year-old extension affect my mortgage?
It might. Some lenders ask for planning or building regulations evidence, while others accept alternative documentation or indemnity insurance.
Should I get a survey of an old extension with no paperwork?
Yes. A survey can identify structural or construction problems that planning records won't reveal.
Can I get indemnity insurance for an old extension without planning permission?
Sometimes. Availability depends on the insurer and circumstances. Indemnity insurance does not confirm the extension is lawful.
Can an old extension affect my property's value?
It might. Missing approvals can concern buyers and lenders, while clear evidence and good condition can reduce uncertainty.
Can I demolish an old extension and build a larger one?
Yes, but the replacement needs its own planning assessment. The existing extension's age does not automatically permit a larger replacement.
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