Permitted development breaches and the immunity period

If a rear extension is 200 millimetres deeper than Class A allows, the whole extension is unauthorised development, not the 200 millimetres. Permitted development rights work as a package: meet every limit and condition and the development is permitted, miss one and nothing in the class protects you. That is the uncomfortable starting point for any permitted development breach immunity question, and it is why the clock on enforcement action matters so much to householders who find out late.

The clock itself changed in England in 2024. The old four year rule for building work has gone for anything completed since then, replaced by a single ten year period. Which rule applies to you depends on when the work was substantially completed rather than on when the council found out.

Why exceeding a class limit makes the whole thing unauthorised

Each class in Schedule 2 to the General Permitted Development Order 2015 grants permission subject to limitations and conditions. The limitations are the numbers: depth, height, area, proportion of curtilage. The conditions are the obligations, such as using materials of similar appearance or obscure glazing in a side-facing window.

Break either and the grant does not apply. The development then needs express planning permission, and without it there is a breach of planning control under section 171A of the Town and Country Planning Act 1990.

Common breaches on householder work are depressingly predictable:

• An extension built to the drawn dimension while the drawing measured from the wrong wall face.
• An outbuilding that takes the total built area over the 50 per cent curtilage limit once the existing shed and the extension are counted in. The arithmetic behind the 50 per cent curtilage rule for garden outbuildings catches more schemes than any single dimension.
• A roof light fitted below the minimum height above the floor of the room.
• Front garden paving laid in impermeable material above the area threshold, where the permeable surfacing requirement under Class F was missed.
• An outbuilding occupied as a separate dwelling, which is a change of use rather than a building limit problem.

That last one is a different kind of breach, and it matters for the immunity analysis, because use breaches and building breaches were treated differently under the old rules.

The immunity periods and what changed in 2024

Section 171B sets the time limits for taking enforcement action. Historically there were two: four years for operational development and for a change of use to a single dwellinghouse, and ten years for everything else, including other changes of use and breaches of condition.

The Levelling-up and Regeneration Act 2023 replaced that with a single ten year period in England. As at the date of writing, the change applies to development substantially completed, or a change of use occurring, on or after 25 April 2024. Work completed before that date keeps the shorter four year protection. Provisions in that Act have been brought into force piecemeal, so check the current position on legislation.gov.uk rather than relying on a summary.

Two details decide most real cases. For building work the period runs from substantial completion, not from the start, and not from when the scaffolding came down. For a use, the period runs from when the use began and it has to have continued without material interruption since.

Immunity is also specific to what was built. An extension that becomes immune does not carry with it a later alteration, and a use that becomes immune does not legitimise a change in its character.

Proving immunity, and who carries the burden

The burden sits with the person asserting immunity, on the balance of probability. Councils do not have to disprove it.

Evidence that works, roughly in order of weight:

1. Dated building invoices, delivery notes and payment records naming the work.
2. Dated photographs, ideally with something in frame that fixes the date.
3. Aerial and street-level imagery with a capture date recorded by the supplier.
4. Council tax, utility or insurance records showing occupation of a separate unit from a given date.
5. Statutory declarations from the owner, the builder and neighbours, setting out what they saw and when.

A statutory declaration from the applicant alone can be enough where there is nothing to contradict it, which is the practical effect of the approach taken in the planning case law on certificates. But a declaration that says "around 2017" will not fix a date, and a council faced with vague evidence is entitled to refuse.

Keep the records in a file from the start rather than reconstructing them later. Owners who kept the builder's invoices get certificates. Owners who paid cash and took no photographs usually do not.

Certificates of lawfulness for immune development

Immunity from enforcement is not the same as lawfulness recognised on paper, and a buyer's solicitor will want the paper. Section 191 of the Town and Country Planning Act 1990 allows an application for a certificate of lawfulness of existing use or development, and section 192 does the same for proposed works.

The application is determined on evidence and law, not on planning merits. The council cannot refuse because it dislikes the extension, and it cannot impose conditions. It either accepts that the development is lawful or it does not.

Three practical points. The fee differs from a planning application fee and depends on the category of development, so check the current schedule. A refusal can be appealed to the Planning Inspectorate, where the evidence is tested again. And an application puts the council on notice of the breach, so make it only when the evidence is ready.

Where the time limit has not yet expired, applying for a certificate tells the authority exactly where to look. In that situation a retrospective planning application under section 73A is usually the better route, supported by a short Planning Statement that addresses the planning merits rather than the dates.

Deliberate concealment and planning enforcement orders

The time limits can be extended where a breach has been deliberately concealed. Sections 171BA to 171BC allow a local planning authority to apply to a magistrates' court for a planning enforcement order, which reopens the enforcement window even where the ordinary period has expired.

The provisions were introduced after a case in which a dwelling was built inside what appeared to be an agricultural building and kept hidden until the four years had run. The courts have been willing to look at the substance of what the owner did, not only at whether a technical deception occurred.

So the strategy of keeping quiet and waiting out the clock carries a real risk, and it gets worse if the owner has actively misled the authority. Honest non-disclosure, where nobody asked and nothing was hidden, is a different matter from screening a building from view or giving false information in correspondence.

Breaches where no immunity applies

Several consent regimes sit alongside planning, and the section 171B periods do not help with any of them.

• Works to a listed building without listed building consent are a criminal offence, and the planning enforcement time limits do not operate in the same way. There is no point at which unauthorised alterations to a listed building simply become acceptable.
• Cutting down, topping or lopping a tree protected by a tree preservation order is a criminal offence in its own right.
• Building Regulations compliance is separate, and a regularisation application is the route there.
• Restrictive covenants and party wall obligations are private law matters that the planning system does not touch.
• An unauthorised use in breach of a licence, such as an unlicensed house in multiple occupation, remains unlicensed however long it has run.

An outbuilding used as an independent dwelling raises both planning and other regimes at once, which is why the separate planning unit problem with garden offices is more serious than a dimension breach.

Correcting a breach before it is noticed

If the breach is recent and small, fixing it is usually quicker and costs less than arguing about it. Three routes, in ascending order of effort.

Reduce the development to within the class limits. Taking 200 millimetres off a flat roof overhang or removing a section of decking can bring the whole thing back inside permitted development, and no application is then needed.

Apply retrospectively under section 73A. This is a normal planning application for development already carried out, assessed on its merits, with the usual fee and consultation. Approval cures the breach completely.

Negotiate. Where an authority has already written, a conversation about what it would accept often produces a narrower solution than a formal notice. Councils have discretion over whether enforcement is expedient, and a cooperative owner with a drawing showing a modest change is in a better position than one who ignores the letter.

Enter your postcode on PlanScope to see which documents a retrospective householder application is likely to need.

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