Planning statement for a Green Belt householder extension
The Green Belt householder test is whether an extension is a disproportionate addition over and above the original building. Here is how to measure it and structure the statement.
A green belt extension planning statement has one job: to show that what you propose is not a disproportionate addition over and above the size of the original building. The National Planning Policy Framework treats extensions and alterations to a building as an exception to inappropriate development in the Green Belt, provided they pass that test. Get the measurement and the comparison right and most householder schemes are winnable. Get the baseline wrong and the statement argues the wrong case from the first page.
The test and the baseline
The exception applies to the extension or alteration of a building where the result is not a disproportionate addition over and above the size of the original building. Two words carry the weight.
Disproportionate is not defined nationally. It is a planning judgement, and most councils give it content through a local plan policy or a householder design guide that sets a percentage of volume or footprint above which an addition is treated as disproportionate. Those local figures vary widely, so find the adopted policy and quote it rather than assuming a familiar number from another district.
Original building means the building as it stood on 1 July 1948, or as built if it was built after that date. Not as you bought it. A 1970s rear addition, a 1990s garage conversion and a 2008 conservatory all count against the allowance even though they were lawful when built, and even though some were permitted development.
Measuring against the original dwelling
Establish the original footprint and volume before drawing anything. The evidence usually comes from a combination of historic Ordnance Survey extracts, the council's own planning history for the address, aerial imagery, and the physical fabric where changes in brickwork or roof line are visible.
Set out the measurement in a table in the statement: the original building, each subsequent addition with its date and approximate volume, the current total, and the proposed total with the percentage increase over the original. Give the method, whether you measured to external faces, and how you treated the roof void and any below-ground element.
Two practical points. Where the original building cannot be established from records, say so and explain the assumption rather than presenting a figure as certain. And check whether the council measures volume, footprint, floorspace or all three, because the same scheme can pass one test and fail another.
Volume, footprint and which one bites
Volume tends to favour single-storey schemes with low roofs and penalise anything with accommodation in the roof. Footprint penalises spreading sideways and is indifferent to height. Floorspace ignores both and rewards nothing.
That means the design response depends on which measure the local policy uses. A council working on volume will often accept a wider single-storey rear extension than one working on footprint, and a council working on footprint may prefer a two-storey element over a sprawling ground-floor plan.
Say in the statement which measure the policy uses, apply it, and then show the others for completeness. An officer who can check your arithmetic in two minutes is an officer who does not refuse for lack of information.
Openness and visual impact
Passing the proportionality test is necessary but not sufficient. The courts have confirmed that openness has both a spatial and a visual dimension, so a scheme can be modest in volume and still harm openness through its position, its prominence in longer views or the way it fills a gap between buildings.
Address it directly. Describe where the addition sits in relation to the existing envelope, what is visible from any public vantage point, and what screening exists or is proposed. Photographs from the nearest footpath and road, with the viewpoint marked on a plan, do more than any adjective.
Garden land matters here too. Extending into an open rear garden that reads as part of the wider countryside has a different effect from infilling a courtyard already enclosed on three sides. Say which situation yours is.
Previous extensions and cumulative effect
Councils assess cumulatively. Each previous addition reduces what remains available, and a series of modest extensions can exhaust an allowance without any single one having been large.
List them with dates and references. Where a previous addition was permitted development rather than the subject of an application, say so and evidence it, because officers will otherwise treat an unexplained structure as suspect. Where a previous permission was granted on the basis that no further extension would follow, expect that history to be quoted back.
One point in the applicant's favour is often overlooked. Green Belt land is not article 2(3) land, so Green Belt designation by itself does not remove householder permitted development rights under Part 1. A scheme that would be disproportionate under local policy may still, in part, be achievable as permitted development, and comparing the two is a legitimate fallback position to set out. Check for an article 4 direction and for conditions on earlier permissions that removed those rights, since both are common on Green Belt plots.
Very special circumstances where needed
If the addition is disproportionate, the exception does not apply and the proposal is inappropriate development. Inappropriate development is by definition harmful and should not be approved except in very special circumstances, where the harm is clearly outweighed by other considerations.
Very special circumstances is a high bar and it is rarely met by a householder scheme on convenience grounds. Where it is arguable, the case is usually built on a specific and evidenced need, such as accommodation for a dependent relative with a documented care requirement, combined with a demonstration that no less harmful option exists. Attach the evidence. An assertion about family circumstances with no supporting letter does not move the balance.
Be honest about the harm as well. A statement that concedes a measurable loss of openness and then explains why other factors outweigh it reads far better than one that pretends the effect is nil.
Structuring the statement for the officer
Keep it short and put it in the order the officer will assess it.
- Site and planning history, with the original building identified and every addition listed by date.
- The measurement table and the method used.
- The relevant development plan policy quoted, with the Framework edition stated.
- The proportionality assessment against the policy measure.
- Openness and visual impact, with photographs and viewpoints.
- Design, materials and relationship to the host dwelling.
- Neighbour amenity, and any other material considerations.
- Conclusion on the Green Belt test, and any fallback position.
Illustrative example: a detached 1930s house with an original volume established from a 1938 extension drawing held in the council's file. A 1985 garage and a 2004 rear addition already account for a 28 per cent increase. The proposed single-storey side and rear wrap takes the total to 46 per cent against a local guide figure of 50 per cent, so the statement leads with the table, then deals with openness from the lane. Granted at delegated level.
Our note on structuring a planning application cover letter covers how to introduce the bundle, and the statement itself should sit alongside a proportionate Design and Access Statement where one is required. For the drafting, the Planning Statement page sets out what the document contains and who should review it.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What counts as the original building?
The building as it stood on 1 July 1948, or as originally built if later. Not the property as you bought it. Extensions added since then count against the allowance even where they were permitted development or were lawfully approved, which is why establishing the baseline from historic mapping and the planning file comes before any design work.
Is there a national percentage for disproportionate additions?
No. The Framework leaves it as a planning judgement, and most councils give it content through a local plan policy or householder design guide expressed as a percentage of volume or footprint. Those figures vary widely between authorities, so quote the adopted local policy rather than a figure carried over from another district.
Can a modest extension still harm openness?
Yes. Openness has a spatial and a visual dimension, so a scheme that passes the proportionality test can still be refused on its position, prominence in longer views or the way it fills a gap between buildings. Deal with it directly using photographs from public vantage points, with the viewpoints marked on a plan.
Do I have permitted development rights on a Green Belt plot?
Green Belt is not article 2(3) land, so designation by itself does not remove householder rights under Part 1 of the General Permitted Development Order. Check for an article 4 direction and for conditions on earlier permissions that removed those rights, as both are common on Green Belt properties. A permitted development fallback can be a legitimate argument.
When are very special circumstances arguable?
Rarely for convenience. Where the case is arguable it usually rests on a specific and evidenced need, such as accommodation for a dependent relative with a documented care requirement, combined with evidence that no less harmful option exists. Attach the supporting letters, because an unevidenced assertion does not shift the balance.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.