Built beyond the permitted development limits: options

If you have built beyond permitted development limits, the first thing to understand is the scale of the problem. Exceeding a limit in Schedule 2 Part 1 of the GPDO 2015 does not make the excess unauthorised while the rest stays lawful. The extension as built falls outside the right altogether, so the whole structure is development without planning permission. A rear extension 3.4 metres deep on a semi-detached house, where the limit is three metres, is an unauthorised 3.4 metre extension rather than a lawful three metre one with a 400 mm problem.

That sounds worse than it usually is. Most of these situations resolve, and the routes are well worn.

Establish which limit was exceeded, and by how much

Before anything else, measure. Get a measured survey rather than relying on the builder's drawings, because the discrepancy is often different from the one you have been told about.

The limits people breach most often on a householder extension are the depth of a single-storey rear extension, the overall height, the eaves height where the extension sits within two metres of a boundary, the side extension width against half the width of the original dwelling, and the proportion of the curtilage covered by buildings. The last of those is the sneakiest, because a garden room built three years ago counts towards it, and how the curtilage is measured on an enlarged garden decides whether you are over the line at all.

Two definitional points catch people. The original dwellinghouse means the house as first built or as it stood on 1 July 1948, so a 1980s extension by a previous owner has already consumed part of your allowance. And height is measured from the highest part of the adjacent ground level, which on a sloping plot is not where anyone assumed.

Write the measurements down with a plan. Everything that follows depends on being precise about the breach rather than approximate.

Applying retrospectively, and the risks

Section 73A of the Town and Country Planning Act 1990 allows an application for planning permission for development already carried out. It is an ordinary planning application in every other respect: the same forms, the same publicity, the same consultation with neighbours, the same eight-week target for a householder application.

The application is judged on its planning merits as if the extension were proposed. That is the good news, because most extensions that marginally exceed a limit are perfectly acceptable in planning terms. Depth, height and materials that would have been approved on an application are still approvable after the event.

Three risks are worth naming plainly. Neighbours are consulted, and an extension that has already annoyed them will attract objection that a paper proposal might not have. The application puts the breach on the public record, which matters if you were relying on time passing. And fees for retrospective applications have been changed more than once and are indexed annually, so check the current schedule before budgeting.

Where an enforcement notice has already been issued, the position narrows and recent reform has restricted the ability to run parallel routes. Take advice on the current procedural position before submitting anything.

Certificates of lawfulness where time has passed

If the works are old enough to be immune from enforcement, the route is a certificate of lawful existing use or development under section 191 of the 1990 Act rather than a retrospective application. The certificate confirms that the works are lawful, which is what a buyer's solicitor wants, and it does not involve any assessment of planning merits.

The burden of proof sits with the applicant and it is on the balance of probabilities. What persuades a council is documentary evidence tied to dates: dated photographs, building materials invoices, council tax or rates records, a builder's statement, utility connection records, aerial imagery. Statutory declarations from neighbours help, and they help most when they are specific about the year and the season.

Enforcement time limits after the 2023 Act

This is where the law changed recently and where old advice is dangerous.

Historically, operational development such as an extension became immune from enforcement after four years, while other breaches took ten. The Levelling-up and Regeneration Act 2023 replaced the four-year rules in England with a single ten-year period, and that change took effect on 25 April 2024. Transitional arrangements mean that breaches which had already become immune, or where the four-year period was already running, are treated differently from breaches occurring after that date.

So the year the extension was built now governs the answer, and the answer is not the one most householders have read online. An extension completed in 2019 was on the four-year track. One completed in 2025 is on the ten-year track. Check the specific date and the transitional provisions rather than assuming either.

Building regulations run on their own clock. The Building Safety Act 2022 extended the time limit for prosecution under the Building Act 1984 to ten years, so a completion certificate problem outlasts what people expect.

Talking to the enforcement officer

Enforcement is discretionary. A council must consider whether taking action is expedient, and national guidance expects a proportionate response to the harm caused. A 400 mm breach on a rear elevation nobody can see is not a priority for an enforcement team with a caseload of unauthorised HMOs and hoardings.

Approach it that way. Contact the officer, describe what happened, provide the measured survey, and say what you propose to do. Officers are far more receptive to an owner who arrives with a survey and a plan than to one who arrives with an argument.

Be careful with a planning contravention notice if you receive one. It is a formal request for information under section 171C, failing to respond is an offence, and what you say in response is evidence. Answer it accurately and take advice before you do.

What you are usually seeking is an agreement that the council will hold enforcement action while a retrospective application is determined. That is a common and sensible outcome, and it is much easier to reach at the start than after a notice has been drafted.

Cutting the works back

The option nobody suggests first often costs the least. Reducing the extension so that it complies with the relevant limit restores permitted development status, and on a marginal breach the building work may be modest.

Whether it is viable depends on which limit was breached. Depth and width reductions mean taking down and rebuilding a wall, which is disruptive but bounded. An eaves height breach near a boundary can sometimes be resolved by altering the roof form. A curtilage coverage breach can be resolved by removing an outbuilding, which may cost almost nothing.

Get a builder's price for the reduction alongside the cost and risk of the retrospective route, and compare them properly. An illustrative example. A rear extension on a 1930s semi built to 3.45 metres against a three metre limit, with a neighbour who had objected to the original informal drawings. The retrospective application carried a real risk of refusal on amenity grounds. Taking the rear wall back 500 mm cost less than the appeal would have, and the works then sat inside the right with no application at all.

Selling the house afterwards

The property information form asks about alterations and about planning and building regulations consents, and answering it inaccurately creates a misrepresentation problem that outlives the planning issue entirely.

What a buyer's solicitor will accept, in rough order of preference, is a retrospective planning permission, a certificate of lawful development, or an indemnity policy. Indemnity policies for missing planning permission are generally available only where the enforcement period has expired and no council contact has taken place, which is exactly why an approach to the enforcement officer needs to be a considered decision rather than a reflex.

Where the extension was built under the prior approval route for a deeper single-storey extension, check whether that approval was implemented in time, because what happens when a prior approval lapses determines whether you were building under a right at all. And if the original permission carried a condition removing permitted development rights, the position is different again, and removing a condition that withdrew permitted development rights is a separate application in its own right.

For a retrospective application, a short planning statement that sets out the breach honestly, explains the amenity position and addresses the neighbour's concerns will do more than extra drawings. Officers respond to candour in these applications because they see the alternative every week.

Enter your postcode on PlanScope to see which reports your site is likely to need. This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.