Evidencing permitted development for a proposed works certificate

A lawful development certificate for proposed works decides one question: would the thing you have drawn be lawful if you built it. Nothing else. Under section 192 of the Town and Country Planning Act 1990 the council is not weighing design, neighbour amenity or the effect on the street. It is checking your drawings against the wording of the General Permitted Development Order, and the onus of proving the case sits squarely with you.

That makes it a documentation exercise rather than a persuasion exercise, and it is why applications fail on missing dimensions far more often than on the merits of the extension.

What the certificate does and does not do

A section 192 certificate confirms that a described operation or use would be lawful. Once granted, it binds the authority in respect of the development described, provided you build exactly what was described.

Two limits are worth knowing. The certificate covers what is on the approved drawings, so a change on site takes you outside it. And it is not a building regulations approval, a party wall award or a check on your covenants, none of which the planning system touches.

There is no discretion in the decision. If the proposal fits within the class, the certificate must be issued. If it does not, it must be refused, however reasonable the proposal looks. Officers who suggest that the extension is a bit large for the plot are commenting on something they cannot lawfully take into account.

Drawings and dimensions the council needs

This is where most applications come unstuck. The council cannot grant a certificate for a proposal it cannot measure.

Submit existing and proposed plans and elevations at a stated metric scale, on a common sheet size, with figured dimensions rather than dimensions the officer has to scale off. The set should show:

• The footprint of the original dwellinghouse, distinguished from later additions
• Depth of the proposed extension measured from the original rear wall
• Overall height, eaves height, and the eaves height of any part within two metres of a boundary
• Distance from every boundary, and which boundary is which
• Existing and proposed ground levels where the ground falls
• Roof form, pitch and ridge height against the existing roof
• Materials, described well enough to show they are similar in appearance to the existing house
• A curtilage plan showing the area of the curtilage covered by buildings, where the fifty per cent limit is in play

Add a short covering statement that walks through each limitation and condition in the class and says how the proposal satisfies it, with the drawing reference for each. Officers approve those quickly because the work has been done for them. A Planning Statement style document does the job, though it should be structured as a compliance schedule rather than as a planning argument, because planning merits are irrelevant here.

Proving what the original dwellinghouse was

Permitted development limits are measured against the original dwellinghouse, meaning the house as it was first built or as it stood on 1 July 1948, whichever is later. Not as it stands today.

On a house that has been extended twice since the 1960s, establishing that baseline is the substance of the application. Useful evidence includes historic Ordnance Survey mapping, the council's own planning history for the property, aerial photography, deed plans, and old sale particulars. Where the property is a post-war estate house, the original builder's type drawings sometimes survive in the local archive.

Where earlier extensions used up part of the allowance, say so and show the arithmetic. An application that ignores a 1994 conservatory the officer can see on the council's own records loses credibility for everything else in it.

Check the constraints in the same exercise. On land defined in Article 2(3) of the Order, which covers conservation areas, National Parks, National Landscapes and World Heritage Sites, several householder rights are removed or narrowed, and an Article 4 direction may have removed more.

Statutory declarations and when they help

Statutory declarations carry weight where the question is about historical fact, which is mostly the territory of certificates for existing development under section 191.

They can still help on a proposed works application in one situation: where the planning history is incomplete and you need to establish when an earlier extension was built, or that a structure was removed. A declaration by a long-standing neighbour, or by the previous owner, giving dates and describing what they saw, is admissible evidence and councils do accept it.

Make it specific. A declaration saying the conservatory was there when I moved in helps far less than one giving the year of purchase, the condition of the structure and a dated photograph exhibited to it.

The fee and the eight weeks

The fee for a certificate for proposed works is set by the current fee regulations at half the fee that would be payable for a planning application for the same development, and fees are indexed annually, so check the current schedule rather than an older figure.

The determination period is eight weeks. There is no publicity requirement in the way there is for a planning application, because neighbours' views are not a relevant consideration, though some councils notify anyway.

Applications are made through the national planning application service in the same way as any other, with the ownership certificate completed and the drawings attached.

If it is refused

A refusal is appealable to the Planning Inspectorate under section 195 of the 1990 Act. These appeals are decided on the law and the facts, which makes them different in character from a planning appeal, and they are frequently won where the council has misread a limitation.

Before appealing, read the refusal reason carefully. Where the council says the drawings do not demonstrate compliance, the faster fix is usually a fresh application with the missing dimension. Where the council says the proposal exceeds a stated limit and you disagree on the interpretation, an appeal is the right route.

Why the certificate matters when you sell

The practical value shows up years later. A buyer's solicitor asks what authorises the extension, and permitted development on its own is an answer nobody can verify from the file.

A certificate is verifiable. It sits in the local land charges register, it names the drawings, and it removes the argument. The alternative offered on many sales is indemnity insurance, which covers the buyer's loss and does nothing to make the building lawful.

There is also an enforcement point. Where works are unauthorised, the time limits for enforcement action have been extended by the Levelling-up and Regeneration Act 2023, so relying on the passage of time is a weaker strategy than it once was. Get the certificate before you build.

Browse the report types on PlanScope to see what a householder application needs where the works fall outside permitted development, or enter your postcode to check the constraints on your site first.

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.