Free tool

Can you build it without planning permission?

Tests an extension, loft, porch or outbuilding against the permitted development limits of Classes A to G and AA.

What kind of home is it?
Why this matters
Part 1 of Schedule 2 to the General Permitted Development Order 2015 gives these rights to a dwellinghouse. A flat or maisonette, or a building containing flats, is not a dwellinghouse for this purpose (article 2(1)). The kind of house sets some limits: a single-storey rear extension may project 4 m on a detached house and 3 m on any other (paragraph A.1(f)(i)), and a roof enlargement may add 40 m³ to a terraced house and 50 m³ to any other (paragraph B.1(d)).
Was the house created under permitted development, rather than with a planning application?

Such as a barn, shop or office converted into a home without a planning application. The planning history will say.

Why this matters
Homes created by a change of use under Part 3, Classes G, M, MA, N, P, PA or Q, of the General Permitted Development Order 2015, or built under Part 20 (new homes on top of, or in place of, other buildings), have no Part 1 rights (paragraph A.1(a) and (l), and the same paragraphs in each Class). Class AA also excludes homes created under Part 3, Class O. A home created with a planning application keeps its rights.
Is the house on Article 2(3) land, such as a conservation area?

Article 2(3) land is a conservation area, National Park, National Landscape, the Broads or a World Heritage Site. Not sure? The planning constraints checker looks it up from your postcode.

Why this matters
Article 2(3) of the General Permitted Development Order 2015 and Schedule 1, Part 1 define this land. On it there is no side extension, no rear extension of more than one storey and no cladding (paragraph A.2), no larger home extension scheme (paragraph A.1(g)), no roof enlargement (paragraph B.1(f)) and no extra storeys (paragraph AA.1(b)), and outbuildings and flues are limited further (paragraphs E.2, E.3 and G.1(c)). A National Landscape is the new name for an area of outstanding natural beauty, the term the Order still uses.
Is the house, or anything within its curtilage, a listed building?

The curtilage is the land that belongs with the house, usually its garden and grounds. Not sure? Search the National Heritage List for England.

Why this matters
A listed building is on the national list of buildings of special architectural or historic interest. Any work that affects its character, inside or out, needs listed building consent, whatever the planning answer (Planning (Listed Buildings and Conservation Areas) Act 1990, section 7). Class E does not apply within the curtilage of a listed building (paragraph E.1(g)).
Has an Article 4 direction or a planning condition removed permitted development rights here?

An Article 4 direction is a council direction that removes named permitted development rights. The planning history and the council's website show both.

Why this matters
Article 4 of the General Permitted Development Order 2015 lets a council direct that named permitted development rights do not apply in an area. A condition on an earlier planning permission, for the house or an extension to it, can remove them for one house. Where either covers the work, it needs a planning application. The checker cannot see which rights were removed.
What do you want to build?

You will only be asked the questions that apply to your project.

Why this matters
Each kind of project is a Class of Schedule 2, Part 1 to the General Permitted Development Order 2015, with its own limits: Class A enlargements of the house, Class AA extra storeys, Class B roof enlargements, Class C other alterations to the roof, Class D porches, Class E outbuildings, Class F hard surfaces, and Class G chimneys, flues and soil and vent pipes.
Will it join an existing extension to the original house?

The original house is the house as first built, or as it stood on 1 July 1948 if built before then.

Why this matters
Article 2(1) of the General Permitted Development Order 2015 defines the original dwellinghouse: the house as it was first built, or as it stood on 1 July 1948 if it was built before that date. Any extension added since counts. Paragraph A.1(ja) applies the limits to the new part together with any existing enlargement it joins, measured from the original house.
Is the house on a Site of Special Scientific Interest?

A Site of Special Scientific Interest (SSSI) is land protected for its wildlife or geology. The planning constraints checker looks it up from your postcode.

Why this matters
The larger home extension scheme (paragraph A.1(g)) and extra storeys under Class AA (paragraph AA.1(b)) are not available on a Site of Special Scientific Interest.
What kind of roof enlargement?
Why this matters
Class B covers an addition or alteration to the roof that enlarges it. A dormer must keep, or put back, the eaves of the original roof and be set back from them (paragraph B.2(b)(i)), so the checker asks which kind.
Is it solar panels?
Why this matters
Class C does not cover solar photovoltaics or solar thermal equipment (paragraph C.1(d)(ii)). Part 14 of Schedule 2 to the General Permitted Development Order 2015 sets their limits.
What will it be used for?

Incidental means used alongside the house, not as a bedroom, annexe or separate home.

Why this matters
Class E allows buildings required for a purpose incidental to the enjoyment of the house (paragraph E(a)). Primary living accommodation is not incidental, so a bedroom, annexe or separate home needs planning permission (Class E, and paragraph E.1(i)).
What form of roof will it have?
Why this matters
The maximum height under Class E depends on the roof: 4 m for a dual-pitched roof and 3 m for any other, but 2.5 m for a building within 2 m of a boundary of the curtilage, whatever its roof (paragraph E.1(e)).
Will the surface be between the principal elevation and a highway?

The principal elevation is usually the front of the original house. A highway includes a road, footpath or private way.

Why this matters
Class F sets a condition only for a hard surface on land between a wall forming the principal elevation and a highway: over 5 m², it must be porous, or drain to a permeable or porous area within the curtilage (paragraph F.2). For Part 1 a highway includes an unadopted street or a private way (paragraph I).
When was the house built?
Why this matters
Class AA applies only to a house built between 1 July 1948 and 28 October 2018 (paragraph AA.1(c)).
How many storeys does the house have now?
Why this matters
A house of one storey may add one storey, and its roof rise by up to 3.5 m; a house of two or more storeys may add up to two, and its roof rise by up to 7 m (Class AA(a) and (b), paragraph AA.1(f)).
How wide is the original house?

Measure across the original house, side wall to side wall, leaving out any later extensions.

Why this matters
A side extension may be no wider than half the width of the original house (paragraph A.1(j)(iii)), so the checker needs this width first.
How wide will the side extension be?

Measure from the side wall of the original house to the outside face of the extension.

Why this matters
A side extension may be no wider than half the width of the original house, must be single storey, and may be no more than 4 m high (paragraph A.1(j)). It is not permitted on Article 2(3) land (paragraph A.2(b)).
What will the rear projection be?

How far the extension reaches beyond the rear wall of the original house, counting any extension it joins.

Why this matters
Class A allows a single-storey rear extension to project up to 3 m beyond the rear wall of the original house, or 4 m for a detached house (paragraph A.1(f)(i)). Up to 6 m, or 8 m for a detached house, is possible under the larger home extension scheme, which needs the council's prior approval and is not available on Article 2(3) land or a Site of Special Scientific Interest (paragraphs A.1(g) and A.4). A rear extension of more than one storey may project up to 3 m (paragraph A.1(h)(i)). Earlier extensions count against the limit (paragraph A.1(ja)).
What will the maximum height be?

The maximum height is the highest part of the roof, measured from the ground next to the extension.

Why this matters
A single-storey rear extension and a side extension may each be no more than 4 m high (paragraphs A.1(f)(ii) and A.1(j)(i)). No extension may be higher than the highest part of the roof of the existing house (paragraph A.1(c)).
What will the eaves height be?

The eaves are where the outside wall meets the roof; measure from the ground. For a flat roof, measure to the top of the wall.

Why this matters
Within 2 m of a boundary of the curtilage, the eaves may be no higher than 3 m (paragraph A.1(i)). Anywhere, they may be no higher than the eaves of the existing house (paragraph A.1(d)).
How far will it be from the rear boundary?

Measure from the back of the extension to the boundary opposite the rear wall of the house.

Why this matters
An extension of more than one storey may not be within 7 m of any boundary of the curtilage opposite the rear wall of the house (paragraph A.1(h)(ii)).
What will the added roof volume be, including any earlier roof enlargements?

The new space above the original roof, in cubic metres. A box dormer adds roughly half its width times its height times its depth.

Why this matters
The roof may gain no more than 40 m³ over the original roof space on a terraced house, or 50 m³ on any other house, counting earlier roof enlargements (paragraph B.1(d)). Your drawings will give the exact figure.
What will the porch's ground area be, measured externally?

Measure to the outside face of the porch walls.

Why this matters
Class D allows a porch outside any external door with a ground area of up to 3 m², measured externally (paragraph D.1(b)), no part more than 3 m high (paragraph D.1(c)) and no part within 2 m of a boundary with a highway (paragraph D.1(d)).
What will the porch's maximum height be?

The highest part of the porch roof, measured from the ground.

What will the maximum height be?

The highest part of the roof, measured from the ground next to the building.

Why this matters
Class E limits the maximum height to 4 m for a dual-pitched roof and 3 m for any other roof, and to 2.5 m for a building within 2 m of a boundary of the curtilage (paragraph E.1(e)).
What will the eaves height be?

The eaves are where the outside wall meets the roof. For a flat roof, measure to the top of the wall.

Why this matters
The eaves of an outbuilding may be no higher than 2.5 m (paragraph E.1(f)).
What area of hard surface will be laid or replaced?

The new or replaced surface in front of the house, in square metres.

Why this matters
Between the principal elevation and a highway, a new or replaced hard surface of more than 5 m² must be porous, or drain to a permeable or porous area within the curtilage (paragraph F.2).
How far will it rise above the highest part of the roof?

From the highest part of the roof, usually the ridge, to the top of the chimney, flue or pipe.

Why this matters
Class G does not allow a chimney, flue or soil and vent pipe that would rise 1 m or more above the highest part of the roof (paragraph G.1(b)).
How many storeys would you add?
Why this matters
Class AA allows up to two storeys on a house of two or more storeys, and one on a house of one storey, on the principal part of the house only (Class AA(a) and (b), paragraph AA.1(h)).
How much higher will the highest part of the roof be?

From the highest part of the roof now to the highest part afterwards.

Why this matters
The highest part of the roof may rise by no more than 3.5 m on a house of one storey, or 7 m on a house of two or more storeys (paragraph AA.1(f)), and no part may be higher than 18 m (paragraph AA.1(e)).
Will any part be within 2 m of a boundary of the curtilage?

Any boundary of the land that belongs with the house counts: side, rear or front.

Why this matters
Within 2 m of a boundary of the curtilage, the eaves of a Class A extension may be no higher than 3 m (paragraph A.1(i)), and an outbuilding may be no higher than 2.5 m (paragraph E.1(e)(ii)).
Will any part be higher than the highest part of the existing roof, or its eaves higher than the existing eaves?

Compare with the house as it stands now: the highest part of its roof, and its eaves.

Why this matters
An extension may be no higher than the highest part of the roof of the existing house, and its eaves no higher than the eaves of the existing house (paragraph A.1(c) and (d)).
Will it extend beyond the principal elevation, or a side elevation fronting a highway?

The principal elevation is usually the main, front elevation of the original house; on a corner plot it can be another. A side elevation fronting a highway is a side wall facing a road, footpath or private way.

Why this matters
Class A does not permit an extension beyond a wall forming the principal elevation of the original house, or beyond a wall that fronts a highway and forms a side elevation (paragraph A.1(e)). For Part 1 a highway includes an unadopted street or a private way (paragraph I). Where it is not clear which elevation is principal, a lawful development certificate confirms it.
Will it include a veranda, balcony or raised platform?

A raised platform means one more than 0.3 m above the ground, such as raised decking.

Why this matters
None is permitted development: Class A excludes a veranda, balcony or raised platform (paragraph A.1(k)(i)), as do Class B (paragraph B.1(e)) and Class E (paragraph E.1(h)).
Will it extend beyond a roof slope that forms the principal elevation and fronts a highway?

Usually the front roof slope, facing the road.

Why this matters
No part of a Class B enlargement may extend beyond the plane of an existing roof slope that forms the principal elevation of the house and fronts a highway (paragraph B.1(c)).
Will the dormer be set back at least 0.2 m from the eaves?

Measured up the roof slope from the eaves, where the outside wall meets the roof.

Why this matters
So far as practicable, the edge of the enlargement closest to the eaves of the original roof must be at least 0.2 m from them, measured along the roof slope (paragraph B.2(b)(i)(bb)). The eaves of the original roof must be kept or put back (paragraph B.2(b)(i)(aa)).
Will any part extend beyond the outside face of the walls below?

Tiles, gutters, fascias and barge boards do not count.

Why this matters
No part of the enlargement may extend beyond the outside face of any external wall of the original house, unless it joins the roof of a rear or side extension (paragraph B.2(b)(ii)). Roof tiles, gutters, fascias, barge boards and other minor roof details overhanging the wall do not count (paragraph B.4).
Have storeys been added to the house under Class AA?

Class AA allows extra storeys on some houses, with the council's prior approval. The planning history will show it.

Why this matters
Class B does not apply where storeys have been added under Class AA (paragraph B.1(h)).
Will it protrude more than 0.15 m from the roof slope?

Measure at right angles to the roof slope, to the outermost part.

Why this matters
Class C allows an alteration to the roof, such as a rooflight, that protrudes no more than 0.15 m beyond the plane of the original roof slope (paragraph C.1(b)) and is no higher than the highest part of the original roof (paragraph C.1(c)).
Will any part be within 2 m of a boundary with a highway?

A highway includes a road, footpath or private way.

Why this matters
No part of a porch may be within 2 m of any boundary of the curtilage with a highway (paragraph D.1(d)). For Part 1 a highway includes an unadopted street or a private way (paragraph I).
Will any part be forward of the principal elevation of the original house?

The principal elevation is usually the main, front elevation of the original house; on a corner plot it can be another.

Why this matters
Class E does not allow any part of a building on land forward of a wall forming the principal elevation of the original house (paragraph E.1(c)).
Will any part be on land between a side elevation and the boundary of the curtilage?

That is, beside the house rather than behind it.

Why this matters
On Article 2(3) land, Class E does not allow a building on land between a wall forming a side elevation of the house and the boundary of the curtilage (paragraph E.3).
Will buildings more than 20 m from any wall of the house cover more than 10 m² in total?

Count every outbuilding more than 20 m from the house, old and new.

Why this matters
In a National Park, a National Landscape, the Broads or a World Heritage Site, buildings more than 20 m from any wall of the house may cover no more than 10 m² in total (paragraph E.2). The limit does not apply in a conservation area.
Will it have more than one storey?
Why this matters
An outbuilding under Class E must be single storey (paragraph E.1(d)).
Will buildings cover more than half the curtilage, not counting the original house?

The curtilage is the land that belongs with the house, usually its garden and grounds. Count earlier extensions and outbuildings as well as the new work.

Why this matters
Class A and Class E do not allow the area covered by buildings within the curtilage, other than the original house, to exceed 50% of the curtilage, excluding the ground area of the original house (paragraphs A.1(b) and E.1(b)). The original house is the house as first built, or as it stood on 1 July 1948 if built before then.
Will it be porous, or drain to a permeable area within the curtilage?

Porous paving and gravel let water soak through; a lawn or border is a permeable area.

Why this matters
Over 5 m² between the principal elevation and a highway, a new or replaced hard surface must be made of porous materials, or provision made to direct run-off water to a permeable or porous area within the curtilage (paragraph F.2).
Will it be on a wall or roof slope that fronts a highway and forms the principal elevation or a side elevation?

Usually the front of the house, or a side wall or roof slope facing a road.

Why this matters
On Article 2(3) land, Class G does not allow a chimney, flue or soil and vent pipe on a wall or roof slope that fronts a highway and forms the principal elevation or a side elevation (paragraph G.1(c)).
Have storeys already been added above the original house?

The original house is the house as first built, or as it stood on 1 July 1948 if built before then.

Why this matters
Class AA is not available where storeys have already been added above the original house (paragraph AA.1(d)).

About this tool

Describe your house and what you want to build. The checker tests it against each permitted development limit, the national limits for building without a planning application, shows which pass and which fail, draws your project against them to scale, and says how to get certainty. You are only asked the questions that apply to your project.

Jurisdiction
England
Law checked
29 September 2026
Tool version
1.1

Made and maintained by Parallel Architecture, a director-led architectural design practice working from Bristol and Brighton. Each rule is checked against the legislation itself and cited where it is applied. How we write the guides and tools.

General guidance on the law in England from the answers you enter, not advice on your project. Website terms.

What this checker is doing

It follows the national rules for what can be built on a house without a planning application, called permitted development: Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015, Classes A to G and AA.

  1. It stops at flats and maisonettes, because permitted development rights under Part 1 belong to houses only.
  2. It asks whether the house was created under permitted development, by a change of use under Part 3 or built under Part 20, because such houses do not have these rights (paragraphs A.1(a) and (l), and the same paragraphs in each Class).
  3. It asks whether the house is on Article 2(3) land: a conservation area, National Park, National Landscape, the Broads or a World Heritage Site. Several rights are removed or narrowed there (paragraphs A.2, AA.1(b), B.1(f), E.2, E.3 and G.1(c)).
  4. It asks about listing, and about any Article 4 direction or planning condition that removes rights, which it cannot check for you.
  5. It then tests each limit that applies to your kind of project, in the order the Order sets them out, and names the paragraph for each result.
  6. It lists the conditions the work must meet, such as matching materials, and obscure glazing in upper-floor side windows.
  7. It draws your project against the limits, to scale.
  8. It says what would give you certainty: a lawful development certificate, the council's binding confirmation that the work is lawful, or for the larger home extension scheme and extra storeys, the council's prior approval before work starts.

Key rules

Permitted development rights under Part 1 of Schedule 2 to the General Permitted Development Order 2015 belong to houses; flats and maisonettes do not have them (article 2(1)). The limits are measured from the original house: the house as first built, or as it stood on 1 July 1948 if it was built before then.

  • A single-storey rear extension may project up to 3 metres beyond the rear wall of the original house, or 4 metres for a detached house, and be no more than 4 metres high (Class A, paragraph A.1(f)).
  • Under the larger home extension scheme, a single-storey rear extension may project up to 6 metres, or 8 metres for a detached house, with the council's prior approval. The scheme is not available on Article 2(3) land or a Site of Special Scientific Interest (paragraphs A.1(g) and A.4).
  • A rear extension of more than one storey may project up to 3 metres, and may not be within 7 metres of the boundary opposite the rear wall of the house (paragraph A.1(h)).
  • Within 2 metres of a boundary of the curtilage, the eaves of a Class A extension may be no higher than 3 metres (paragraph A.1(i)).
  • A side extension must be single storey, no more than 4 metres high and no wider than half the width of the original house (paragraph A.1(j)).
  • No Class A extension may extend beyond the principal elevation, or a side elevation fronting a highway (paragraph A.1(e)).
  • Buildings other than the original house may cover no more than half of the curtilage (paragraphs A.1(b) and E.1(b)).
  • Class AA allows up to two extra storeys on a house of two or more storeys, or one on a house of one storey, built between 1 July 1948 and 28 October 2018. The roof may rise by no more than 7 metres or 3.5 metres respectively, and prior approval is always needed (paragraphs AA.1(c), AA.1(f) and AA.2(3)).
  • A Class B roof enlargement may add no more than 40 cubic metres to a terraced house, or 50 cubic metres to any other house (paragraph B.1(d)). A dormer must be set back, so far as practicable, at least 0.2 metres from the eaves (paragraph B.2(b)(i)(bb)).
  • A rooflight under Class C may protrude no more than 0.15 metres from the roof slope (paragraph C.1(b)).
  • A Class D porch may have a ground area of up to 3 square metres, be no more than 3 metres high, and have no part within 2 metres of a boundary with a highway (paragraph D.1).
  • A Class E outbuilding must be single storey, with eaves no higher than 2.5 metres and a maximum height of 4 metres for a dual-pitched roof or 3 metres for any other. Within 2 metres of a boundary, its maximum height is 2.5 metres (paragraph E.1).
  • A new or replaced hard surface over 5 square metres between the principal elevation and a highway must be porous, or drain to a permeable area within the curtilage (Class F, paragraph F.2).
  • A chimney, flue or soil and vent pipe under Class G may not rise 1 metre or more above the highest part of the roof (paragraph G.1(b)).

Article 2(3) land is a conservation area, a National Park, a National Landscape, the Broads or a World Heritage Site. On it, side extensions, rear extensions of more than one storey, roof enlargements and cladding are not permitted development (paragraphs A.2 and B.1(f)). An Article 4 direction or a planning condition can remove these rights. A lawful development certificate is the council's binding confirmation that proposed work is lawful.

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