Regularising works already built without permission

If an extension, outbuilding or loft conversion has already been built without permission, you can apply for it afterwards. Section 73A of the Town and Country Planning Act 1990 allows a local planning authority to grant permission for development already carried out, and a retrospective application for a householder is decided on exactly the same merits as one made before the work started.

That last point is the one to hold on to. The council cannot refuse because you built it first. It can only refuse for the planning reasons that would have applied anyway, and being annoyed is not one of them.

The route for an application after the event

A retrospective application uses the same form as a normal householder application, with the description of development written in the past tense: "retention of a single storey rear extension", rather than "erection of".

Everything else is the same. The same plans, the same fee band, the same eight week determination period for a householder application, the same right of appeal if refused. The officer visits, the neighbours are notified, and a decision is issued.

Where only part of the work is unauthorised, apply for that part. Applying for the whole house when a 300 millimetre overhang is the problem invites the council to reopen things that were already lawful.

Whether enforcement is already in prospect

Check this before you do anything else, because it changes the sequence.

If no one has complained and the council knows nothing about it, you are making a straightforward application. If an officer has visited, written to you, or issued a planning contravention notice, you are in an enforcement process and the application becomes part of a negotiation.

If an enforcement notice has already been served, the position is different again. There are strict deadlines for appealing a notice, the grounds of appeal are prescribed, and the ability to argue that permission ought to be granted can be restricted depending on what was applied for and when. Get advice quickly at that point rather than submitting an application and hoping it overtakes the notice.

Time limits matter too. The enforcement time limit in England moved to ten years for all breaches under section 115 of the Levelling-up and Regeneration Act 2023, in force from 25 April 2024, with earlier breaches governed by the previous four and ten year periods. Where works have been in place for a long time, they may already be immune, and the planning law timeline is a reasonable place to follow how that reform has bedded in.

As-built drawings and the measured survey

This is where most retrospective applications go wrong, and it is entirely avoidable.

The drawings have to show what is actually there. Not the drawings the builder worked from, not the design that was discussed, and not a tidied-up version. A council that grants permission for drawings which do not match the building has granted permission for something that does not exist, and the problem returns when the house is sold.

Commission a measured survey. Existing and proposed become existing (before) and as built, at a recognised scale, with dimensions on the critical points: eaves height, ridge height, depth from the original rear wall, distance to the boundary, window positions and sill heights. Take levels where the ground falls.

Photographs from each elevation and from the neighbouring gardens help the officer assess it without a second visit.

One detail that trips people up. The relevant measurement for a rear extension is usually taken from the original rear wall of the house as it was on 1 July 1948 or as first built, not from a later addition. Get that reference point right on the drawing, because an officer who spots the wrong datum will question everything else.

Assessing the works honestly against policy

Now look at the building as an officer would, against the council's householder design guidance and the local plan policies on design and amenity.

The recurring issues are loss of light to a neighbouring habitable room, overbearing impact from a flank wall close to a boundary, overlooking from a new window or roof terrace, and an addition that dominates the original house. On a 1930s semi, a two storey rear extension built hard to the boundary will be tested against the 45 degree line to the neighbour's nearest habitable room window, and if it fails that test, it failed it before it was built as well.

Where a problem exists, deal with it rather than arguing it away. Obscure glazing to a side window, a fixed pane, a reduced parapet, a cut back to the flank wall. Offering a modification in the application is far more effective than defending the building as constructed and then negotiating after a refusal.

A short Planning Statement setting out the policy position and the amenity assessment is useful here, and on anything visible from the street a Design and Access Statement covering materials and proportions does no harm.

Neighbour publicity and the objections to expect

The council will notify neighbours exactly as it would for any other application, and on a retrospective case the objections tend to be sharper because people have been living with the building.

Expect three themes: that the work was done without permission, that it is bigger than was discussed, and that it causes a specific harm. Only the third is a planning matter, and the officer knows that. Your response should address the harm with evidence, and should not argue with the first two.

Talking to the neighbour before submitting is usually worth an afternoon. Not to persuade them to withdraw an objection, which rarely works, but to understand what the actual complaint is. A great many of these disputes turn out to be about a specific window rather than about the extension.

Fees and the second attempt

The application fee is the same as for the equivalent prior application, and fees are indexed, so check the current schedule rather than a figure from a previous job.

The point that catches people is the free go. Normally one further application for the same development on the same site can be made without a fee within twelve months of the first decision. That concession does not apply where the application is retrospective. A second attempt costs full price, which is another reason to get the drawings and the amenity response right the first time.

The wider mechanics of a section 73A application are covered in more detail in the note on retrospective applications under section 73A.

Certificate, application or removal

Three routes, and the right one depends on the facts.

A lawful development certificate is the answer where the works were permitted development all along, or where they have been in place long enough to be immune from enforcement. It confirms lawfulness rather than granting permission, and it is the only formal way to establish that works are lawful.

A retrospective application is the answer where the works need permission and would reasonably get it, with or without modification. This is the common case.

Removal or alteration is the answer where the works plainly conflict with policy and no modification fixes it. Deciding that early, and negotiating what has to change, is far less painful than a refusal followed by an enforcement notice followed by an appeal. Councils will usually discuss a compromise if the approach is made before the notice.

Whichever route you take, do not carry on building. Continuing work that is the subject of enforcement interest makes every subsequent conversation harder.

Enter your postcode on PlanScope to see which documents a householder application 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.

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