10 Permitted Development conditions that apply to all extensions

Transcription of the video

In this video, I describe the 10 conditions common to all extensions built under Permitted Development

An extension is defined as ‘the enlargement, improvement or other alteration of a dwelling house’ and so this video is relevant for side extensions, rear extensions, loft conversions, garage conversions, porches and all types of outbuilding.

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house extensions include garage conversions, porches etc

This is video No 2 in a series of videos that started with Video No 1 considering eligibility for Permitted Development. It is recommended that you watch both videos 1 and 2 before watching any of the following videos:

  • No 3 covering rear extensionsNo
  • 4 Side extensions
  • No 5 Loft conversions
  • No 6 Outbuildings

Note that this video is not relevant to video No 7 Additional Storeys

Here are the 10 Conditions that apply to the extensions in videos 3 to 6

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10 conditions applicable to house extensions

Now, lets look at the detail …

Condition 1: Footprint limit of 50%

Extensions (including any extensions to the original house under Class A or under a separate planning permission) and other buildings must not exceed 50% of the curtilage.

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50% footprint limit

“Curtilage” is land within which the house sits, or to which it is attached, such as the garden. It’s land which is used for the benefit of those living in the house and includes driveways, lawns, vegetable patch etc.

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curtilage of property

Curtilage is unlikely to contain land that is separate, such as woodland or paddocks, which are not considered part of the dwelling even though they may be linked.

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Curtilage excludes woodland and paddocks

In the case of properties with large grounds, the curtilage may be a smaller area, perhaps the area near the house, cultivated as a garden.

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Curtilage of small area in large ground

The maximum area that can be built on as permitted development is 50% of the green area, as shown here, whether as:

  • an extension to the house under class A
  • a roof conversion under class B
  • or outbuildings erected under class E
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maximum area of development is 50%

The 50% limit applies to all buildings so will include existing and proposed outbuildings as well as any existing or proposed new extensions to a house.

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50% footprint limit applies to existing and proposed buildings

The original house is not included in the 50% allowance. Neither is any separate detached building if built together prior to 1948.

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original house not included in 50% limit

For houses built after 1948, the 50% allowance includes separate detached buildings, even if built together.

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houses built after 1948

The 50% allowance always includes later extensions or any later separate detached buildings, irrespective of when they were built.

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separate detached building included in 50% allowance

Condition 2.Overall Height

The extension must not exceed the height of the highest part of the roof of the existing house, which is – the height of the ridge line of the main roof (even though there may be other ridge lines at a lower level) – or where roofs on a building are flat, the height of the highest flat roof.

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Extension height limited to that of existing house

Vertical protrusions, such as chimneys, firewalls, parapet walls are accounted for, as follows: for the existing house, do not include the height of protrusions; for the new extension, do include their height.

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Chimney included in height calculation of new extension

Condition 3.Height of eaves

The height of the eaves of the extension must not exceed the height of the eaves of the existing house.

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Height of extension eaves
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Eaves of extension lower than that of house

On the left, we see the side view of an extension with a pitched roof. The height of the eaves is measured from the ground level at the base of the external wall of the extension to the point where the external wall surface would theoretically meet the upper roof surface.

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Height of eaves measured at theoretical surface junction

On the left, we see the side view of an extension with a pitched roof. The height of the eaves is measured from the ground level at the base of the external wall of the extension to the point where the external wall surface would theoretically meet the upper roof surface. Ground level is the surface of the ground immediately adjacent to the building in question, and does not include anything above the ground, such as decking. Parapet walls and overhanging parts of eaves are ignored in the calculation of eaves height.

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Parapet walls ignored in the calculation of eaves height

Where there is a flat roof, as shown on the right, we measure eaves height in the same way, measuring up to the theoretical junction of external wall surface and roof surface.

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Eaves height of flat roof measured in same way as pitched roof

Where the existing house has eaves of different heights, the level of the eaves for the extension is measured against the highest level of eaves on the existing house.

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Height of eaves measured against highest eaves level of house

Where a house is on sloping ground, the level of the eaves on the existing house is taken at the elevation from which an extension is attached.

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House on sloping ground, eaves measurement

Condition 4.Limits on frontage

The enlarged part of the dwellinghouse cannot extend beyond a wall which (i) forms the principal elevation of the original dwellinghouse; or (ii) fronts a highway and forms a side elevation of the original dwellinghouse

We need to look at these 3 highlighted phrases in more detail:

What does ‘extend beyond a wall’ mean? It refers to both the area immediately in front of the wall plus the area in front of a line drawn from the end of the wall to the boundary of the property.

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Extend beyond wall of principal elevation

Which of these extensions are allowed under PD? These two

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Extensions not allowed in front of principal elevation

How do you decide which is the Principal Elevation? Well, it usually means the front of the house. Often, this is indicated by the existence of prominent architectural features, such as bay windows or a porch serving the main entrance to the house.

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House angled toward highway

If the architectural features do not signal the “Principal Elevation”, it can usually be assumed to be that part of the house which fronts (directly or at an angle) the main highway serving the house (and the main highway is the one that sets the postcode for the house).

Which of these extensions are allowed under PD? These two …

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Extensions allowed on angled house

Where there is an ‘L’ shaped house, the walls in the frontage form the principal elevation and the lines are drawn from these walls.

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principal elevation on L-shaped house

Which of these extensions are allowed under PD? These two

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Allowable extension on L-shaped house

There is only one principal elevation on a house. Where there is a corner plot, a view needs to be taken as to which of the elevations A or B is the principal elevation. You can then identify your rear elevation and this can be a critical decision. In this scenario, the option of adding a long rear extension under PD rules is only available if elevation B is established as the principal elevation.

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Principal elevation on corner house

Bear in mind that you may need to agree the principal elevation with your local planning officer. While part (i) of the condition limits extensions past the principal elevation, part (ii) of the condition limits extensions past the side elevation but only if it fronts a highway. Which of these extensions are allowed under PD? This one

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allowable extensions on corner property

The extent to which a side elevation of a house fronts a highway is dependent on a couple of factors. One factor is the angle between a side elevation of the house and the highway. If that angle is more than 45 degrees, then the elevation is not normally considered to be fronting the highway.

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side extension not fronting the highway

Which of these extensions are allowed under PD? These two

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allowable extensions on angled property

If the angle is less than 45 degrees, then the elevation is normally considered to be fronting the highway.

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side extension fronting the highway

Which of these extensions are allowed under PD? Just this one

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allowable extensions on acutely-angled property

The second factor determining whether a side elevation fronts a highway is the distance between the house and the highway. Where the distance is substantial, it is unlikely that a building can be said to front the highway.

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distance between house and highway

The same may be true where there is a significant area of third party land between the house boundary and the highway.

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third party land between house and highway

Condition 5.The total enlargement

Where the proposed extension is joined to an existing extension to the original house,

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proposed extension is added to existing extension

the total enlargement must meet the limits set out for the specific types of extension.

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total enlargement must meet limits set for all enlargements

These limits are detailed in later more-focussed videos.

Condition 6.Veranda, Balcony and Raised Platform

These structures, verandas, balconies and raised platforms, are not allowed under PD rules. They are defined as follows:

A veranda is a roofed open-air gallery attached to the outside of a building and often partly enclosed. A balcony is a platform with a balustrade, projecting outside an upper storey of a building. A ‘Juliet balcony’ does not have a projecting platform and is therefore allowed under PD rules. A raised platform is any platform with a height greater than 0.3 metres and this includes roof terraces. Note that Class E of the PD rules allows garden decking provided it is not more than 0.3 metres high.

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structures, verandas, balconies and raised platforms

Condition 7.Items specifically excluded by Class A but covered in other classes

Where an extension to a house under Class A includes works that would require an alteration to the existing roof of the house (for example where the roof of the extension joins the existing roof), the alterations to the existing roof of the house will need to meet the requirements of Class B or C in order to be permitted development.

  • Class B covers enlargement of houses through alterations or additions to the roof
  • Class C covers other alterations to the roof of a house
  • Class G covers work on a chimney, flue, soil pipe or vent pipe
  • Class H covers work on a microwave antenna.
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Items specifically excluded

Condition 8: Article 2(3) land

(this land category is explained in video No 1)

Where a house is on article 2(3) land, development is not permitted by Class A if it

  • includes the cladding of any part of the exterior of the house
  • the enlargement extends beyond a side wall
  • the enlargement is a rear extension higher than single-storey.

Condition 9: Materials used in any exterior work

This condition aims to ensure that any works to enlarge, alter or improve a house results in an appearance that minimises visual impact and is sympathetic to existing development. This means that the materials used should be of similar visual appearance to those in the existing house. It does not mean that they need to be the same materials.

The requirement for similar visual appearance does not apply to conservatories.

Condition 10: Solid Wall Insulation

The installation of solid wall insulation constitutes an improvement rather than an extension and is not therefore caught by any exclusions to cladding.

That’s it for this video

In the next one, video No 3, I’ll go through the rules for building rear extensions under Permitted Development.

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Side extensions permitted development video