Building Without Planning Permission: PD Limits, Retrospective Applications, Enforcement

Last updated: September 2026 · Verified against the Town and Country Planning Act 1990 (as amended by the Levelling-up and Regeneration Act 2023) and the Planning Portal fee schedule effective 1 April 2026.

Can you build an extension without planning permission?

Yes — often completely legally. Permitted development rights grant planning permission automatically for a large share of household projects: single-storey rear extensions, most loft conversions, garage conversions and garden outbuildings. Building "without planning permission" is, for many projects, exactly what Parliament intended. The real questions are whether your project fits within the permitted development limits, and what your options are if it does not — or if you have already built something that falls outside them.

Two kinds of people search for this. If you are planning a project and want to know what you can build without applying, start with the limits below. If you have already built — or you are buying or selling a house and a solicitor has flagged missing paperwork — skip to the enforcement and retrospective sections. Both situations are far more fixable than the anxiety suggests, but the fixes are specific, and getting the sequence wrong can cost you.

How far can you extend without planning permission?

The permitted development limits for houses in England, in brief:

• Single-storey rear extension: 3m beyond the original rear wall for a terraced or semi-detached house, 4m for a detached house. Maximum height 4m, and eaves capped at 3m within 2m of a boundary.
• Larger rear extension: up to 6m (terraced/semi) or 8m (detached) via the prior approval route — a £249 application with a neighbour consultation stage.
• Side extension: single storey only, no wider than half the width of the original house.
• Loft conversion: up to 40 cubic metres of added roof space on a terraced house, 50 on a semi or detached — with no extension beyond the roof slope of the principal elevation.
• Outbuildings: single storey, maximum 2.5m high within 2m of a boundary, incidental use only — no self-contained living accommodation.
• The 50% rule: extensions and outbuildings together must leave at least half the land around the original house uncovered.

"Original" means the house as first built or as it stood on 1 July 1948 — previous extensions eat into your allowance even if a former owner built them. Permitted development does not apply to flats or maisonettes at all, and conservation areas and Article 4 directions strip out several classes. The full rules, with the conditions that catch people out, are in our permitted development rules guide, and do I need planning permission for an extension? walks through the decision project by project.

What actually happens if you build without permission

First, the fact that calms most people down: building without planning permission is not a criminal offence. You will not be prosecuted, fined or given a record for putting up an extension that needed permission and did not have it. The one exception is listed buildings, where unauthorised works are a criminal matter from day one.

What you have instead is a breach of planning control, and the council has discretion over what to do about it. In practice, councils usually find out through a neighbour complaint — planning departments do not patrol streets looking for new extensions. When they do investigate, the realistic outcomes are:

• Nothing. If the work would plainly have been approved, or it is immune through the passage of time, most councils will not spend enforcement resources on it. Enforcement is discretionary — councils act where there is planning harm.
• An invitation to apply retrospectively. This is the standard first move. The council writes asking you to regularise the position with a retrospective application, and the case sits on hold while that runs.
• An enforcement notice. The formal tool. It sets out the breach, what you must do about it — which can range from a modest alteration to full demolition — and a compliance period. A notice takes effect no earlier than 28 days after it is served.

You can appeal an enforcement notice to the Planning Inspectorate, but the appeal must be lodged before the notice takes effect — the deadline is hard, and there is no discretion to accept a late appeal. One of the grounds of appeal, ground (a), argues that permission ought to be granted, and running it counts as a deemed planning application with a fee of double the normal application fee. That doubled fee is a good reason to apply retrospectively when invited rather than forcing the council to a notice.

Here is where it does become criminal: ignoring an enforcement notice once it has taken effect is an offence, and councils prosecute for it. The breach itself is a paperwork problem; defying the notice is not. If a notice ever lands, act inside the 28 days — comply, appeal, or negotiate — and never let it take effect unanswered.

The 10-year rule — and why the 4-year rule still matters

Unauthorised development becomes immune from enforcement after a set period. This is the area where most of what you read online is out of date, because the law changed under the Levelling-up and Regeneration Act 2023.

For breaches in England, the position since 25 April 2024 is a single 10-year immunity period — covering operational development (extensions, outbuildings, physical works) and changes of use alike. The old 4-year rule for building works was abolished for new breaches.

The transitional rule is the detail that matters for real houses: work that was substantially completed before 25 April 2024 keeps the old 4-year period. So an extension finished in 2021 became immune in 2025 under the old rule, while an identical extension finished in May 2024 will not be immune until 2034. Any page that tells you flatly "extensions become lawful after 4 years" was written before the law changed — check the date on what you are reading.

Immunity is real but invisible until you prove it. The instrument that converts "probably immune" into a document a buyer's solicitor will accept is a lawful development certificate for existing works — a section 191 application, at £548, where you evidence when the work was completed. Our lawful development certificate guide covers the evidence that wins these applications and the difference between the s191 (existing works) and s192 (proposed works, £274) routes.

Retrospective planning permission: how it works

A retrospective application under section 73A is exactly what it sounds like: you apply for permission for something already built. Three things worth knowing:

• It costs the same as applying in advance. The householder fee is £548, plus the £91.02 Planning Portal processing charge unless you pay the council directly. There is no penalty fee for applying after the event.
• It is judged on planning merits exactly as if you had applied before building. The case officer assesses the extension against the same policies — impact on neighbours, design, amenity. The fact that it already exists is not held against you, and equally it earns no sympathy: "it's already built" is not a planning argument.
• The risk is what a refusal does. Before applying, your unauthorised extension sits in ambiguity and the council may never act. A refused retrospective application removes the ambiguity and puts the breach squarely on the council's desk, with a decision on record that the work is unacceptable. Enforcement becomes much more likely.

That risk is why the choice between a retrospective application and a section 191 certificate matters. If the work is arguably within permitted development, or old enough to be immune, an LDC is usually the better instrument — it is a legal test on evidence, not a planning judgement. Apply retrospectively when the work genuinely needed permission and would plausibly get it. If you are unsure which side of the line you are on, get advice before filing anything, because the wrong application can create the problem it was meant to solve. Fee details for every route are on our planning fees page.

Selling a house with unauthorised work

This is how most people discover a problem: not a council letter, but a buyer's solicitor. The property information form asks whether building work has been carried out and requests the paperwork — planning permission or LDC, plus building regulations sign-off. An extension with no paper trail gets flagged, and the buyer's side will want it resolved before exchange.

Three routes, in ascending order of robustness:

• Indemnity insurance. A one-off policy that pays out if the council later takes enforcement action. It is the common workaround because it is fast — it can be arranged within days and keeps a sale moving. Understand what it is: it insures against the financial consequences of enforcement, it does not make the work lawful, and contacting the council about the work typically invalidates the policy. It papers over the question rather than answering it.
• A retrospective application, where the work needed permission — with the merits risk above, and a timescale that can stretch a nervous buyer.
• A lawful development certificate, where the work was permitted development or is immune under the 4/10-year rules. This is the clean fix: a formal council document stating the work is lawful, which ends the conversation with any future buyer, not just this one.

If you are not under time pressure — you have found old unauthorised work and are not mid-sale — the LDC is almost always worth doing now, on your own timetable, rather than in a panic at exchange.

Building regulations are a separate problem

Planning permission and building regulations approval are two independent regimes, and unauthorised work often fails on both. An extension can be perfectly fine under permitted development and still have no building regulations completion certificate — solicitors flag that just as readily.

The fix on the building regs side is a regularisation certificate: an application to the council's building control team, who inspect the work (sometimes opening up parts of it) and certify it retrospectively if it complies. Councils set their own charges for regularisation, so ask yours directly. And if your unauthorised extension sits on or near a boundary, remember the Party Wall Act is a third separate regime again — a private matter between you and your neighbour that no planning or building regs approval touches.

Frequently asked questions

Is it illegal to build an extension without planning permission?

No — it is not a criminal offence, except on listed buildings. It is a breach of planning control, which the council can act on through an enforcement notice. Ignoring an enforcement notice once it takes effect is a criminal offence, so the danger point is not the building, it is failing to respond to formal action.

Can the council make me demolish my extension?

In principle yes, through an enforcement notice — but demolition is the last resort, used where the harm cannot be fixed any other way. Councils are required to act proportionately, and most cases resolve through a retrospective application or a modification to the work. The notices that end in demolition are typically flagrant cases: whole storeys, buildings in gardens being lived in, work done in defiance of a refusal.

How much does retrospective planning permission cost?

The same as applying in advance: £548 for a householder application in England from 1 April 2026, plus £91.02 Planning Portal processing unless you pay the council directly. There is no surcharge for applying after building.

How long before unauthorised building work becomes immune from enforcement?

Ten years, for breaches in England since 25 April 2024. Work substantially completed before that date keeps the old 4-year period. Immunity is proven with a section 191 lawful development certificate (£548) — see our LDC guide for the evidence councils accept.

Does indemnity insurance make unauthorised work legal?

No. It insures against the cost of enforcement action; the work remains unauthorised. It is a pragmatic tool for keeping a sale alive, but the lawful development certificate is the only document that actually settles the question — and approaching the council usually voids an indemnity policy, so decide which route you are taking before you make contact.

The extension has planning permission but no building regulations sign-off — is that a problem?

Yes, and a separate one. Apply to the council's building control team for a regularisation certificate; they inspect and certify the work retrospectively if it complies. Councils set their own charges for this, so contact yours for a figure.

If you are unsure where your project — built or planned — sits against the permitted development limits, we will tell you straight. Our free site visit checks your PD position — and we can pull your property's planning history with the council — before you commit to anything, and if drawings or an application are needed we handle them through our drawings and planning service. Call 020 3051 9430 or read our complete planning permission guide and current fee schedule first if you prefer to arrive armed.