Which reports a single storey rear extension needs

A single storey rear extension is the lightest thing the English planning system asks you to document. The reports needed for a rear extension usually come down to drawings, a location plan, an ownership certificate and the fee. Nearly every national requirement that triggers a specialist report has a threshold well above a 15 m2 kitchen enlargement, so the pack is small.

What fills the gap is the local validation list. Each local planning authority publishes its own, and those lists differ more than most homeowners expect. One council will want nothing beyond the national minimum. The next will ask for a tree plan, a drainage note and a short design statement before it will even register the application.

What the national validation list requires

The national requirements sit in the Town and Country Planning (Development Management Procedure) (England) Order 2015. For a householder application they are short:

1. The completed application form, signed and dated.
2. A location plan at 1:1250 or 1:2500, with the application site edged red and any other adjoining land in the same ownership edged blue.
3. A block or site plan, usually 1:200 or 1:500, showing the extension against the boundaries and the neighbouring buildings.
4. Existing and proposed floor plans and elevations, normally 1:50 or 1:100, each with a scale bar and a north point.
5. The ownership certificate, A to D, plus the agricultural holdings declaration.
6. The correct fee.

Add the Community Infrastructure Levy additional information form wherever the council charges the levy. A householder extension under 100 m2 is normally exempt from the levy, but the form is how the council records that exemption, and a missing form is one of the commonest reasons an application sits unvalidated for a fortnight.

Scale bars matter more than people think. A drawing marked "1:100 at A3" that has been printed to A4 will be rejected, and the eight week clock does not start until the application is valid.

When a design and access statement is triggered

Article 9 of the 2015 Order sets the trigger, and a single storey rear extension almost never meets it. A Design and Access Statement is required for major development, for listed building consent applications, and for development in a conservation area or World Heritage Site that involves one or more dwellinghouses or 100 m2 or more of floor space. An 18 m2 rear extension in a conservation area meets none of those tests.

Plenty of councils still ask for a short design or planning statement on their local list. If yours does, write it. Two sides of A4 covering the site, the policy context, the design response and the effect on neighbours costs you an evening and removes an argument at validation.

Where no statement is required, the case for the extension has to live somewhere. Put it in the covering letter: how the depth was arrived at, why the ridge sits below the neighbour's, what happens to the rainwater.

Trees on or near the boundary

Two questions decide whether you need arboricultural evidence. Is any tree protected, by a Tree Preservation Order or by standing in a conservation area? And do the works fall inside a tree's root protection area?

The root protection area under BS 5837:2012 is a circle with a radius of twelve times the stem diameter, measured at 1.5 m above ground, capped at 707 m2 in area. A mature sycamore with a 400 mm stem carries a root protection area 4.8 m in radius. Footings 3 m from that trunk sit well inside it, and a case officer who can see the tree on aerial imagery will ask for a BS 5837 tree survey and a tree protection plan before determining the application.

Works to a tree in a conservation area need six weeks' written notice to the council under section 211 of the Town and Country Planning Act 1990, separately from the planning application. Pruning a neighbour's overhanging branch is a civil matter, not a planning one, and councils will not adjudicate it.

Daylight, sunlight and the neighbour's window

Most councils apply a rule of thumb from their householder design guide rather than a formal study. The common version is a 45 degree line drawn in plan from the midpoint of the nearest ground floor habitable room window on the neighbouring property. If the extension crosses that line, the officer will look harder at it.

The technical benchmark behind those rules is BRE 209, Site Layout Planning for Daylight and Sunlight, which sets out a 25 degree vertical section test as the first screening check and vertical sky component and annual probable sunlight hours calculations where that check is failed. A full daylight and sunlight assessment is disproportionate for a single storey extension in almost every case. It becomes worth commissioning when the extension is close to a boundary, deep, and next to a window serving a kitchen or living room that already sits in shade.

Terraced and semi-detached plots are where this bites. A 4 m deep extension on a narrow terrace, built hard to the party boundary, will reach the neighbour's rear window in a way the same extension on a detached plot never would.

Drainage and hard surfacing

New roof area has to go somewhere. Councils increasingly ask for a note on the application form or drawings saying whether surface water will discharge to an existing combined sewer, a separate surface water sewer or a soakaway, and soakaway design still follows BRE Digest 365 in practice.

Hard surfacing in the front garden has its own rule. Under Part 1 Class F of the General Permitted Development Order, laying more than 5 m2 of hard surface between the principal elevation and a highway is only permitted development where the surface is porous or where run-off is directed to a permeable area within the curtilage. Block paving straight to the kerb is a breach, and it is the sort of thing an enforcement officer notices while visiting for something else.

If the property sits in Flood Zone 2 or 3, expect a request for a short flood risk assessment even for a householder extension. Planning Practice Guidance is clear that the sequential test does not need to be applied to householder development, which saves a great deal of argument, but finished floor levels and flood resilient construction will still come up.

Conservation areas and listed buildings

An Article 4 direction can remove householder permitted development rights across a whole conservation area, which changes whether you need permission at all rather than which documents you file. Check the direction itself, because the classes withdrawn vary street by street.

Where the house is listed, the extension needs listed building consent as well as planning permission, and that application does require a design and access statement along with a heritage statement proportionate to the building's significance. The same logic applies to work in the setting of a listed building next door, which is a different test with a different evidence base, covered in our guide to the reports needed for development next to a listed building.

What you almost certainly do not need

Biodiversity net gain does not apply. Householder applications are exempt from the biodiversity gain condition, so no metric calculation and no gain plan. Transport assessments, environmental impact assessment screening, noise reports and air quality work all have thresholds far above a domestic extension.

Ecology is the one exception worth taking seriously. Bats are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017 whether or not a council asks for a survey. If the extension involves stripping a roof, cutting into a soffit or removing a section of tiled roof over an older property, a preliminary roost assessment costs far less than halting work mid-strip after finding droppings.

Permitted development is worth checking before any of this. A single storey rear extension of up to 3 m on a semi-detached or terraced house, or 4 m on a detached house, sits within Class A of the General Permitted Development Order, with the larger 6 m and 8 m depths available through the prior approval neighbour consultation scheme. A lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful.

Enter your postcode on PlanScope to see which of the 66 report types a site is likely to need before you commit to a consultant.

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.