PERMITTED DEVELOPMENT: EXTENSIONS
Does your project qualify for permitted development?
Not all projects need planning permission and a surprising amount of work can be done under permitted development rights. This post is aimed to provide some specific guidance on development criteria and restrictions for domestic extension projects under permitted development.
Extensions are a common type of building carried out under permitted development rights, falling under ‘Class A’ of the technical guidance. The full government published document can be found here: Permitted Development Technical Guidance
If you want to know more about permitted development or are unsure whether your project qualifies, then you can read the introductory post here:
Permitted Development: An Overview
It covers key terms which underpin permitted development rights such as; the ‘original house’, lawful development certificates and designated areas and which are referred to in the remainder of this post.
General conditions applying to all extensions
Extensions are provided under permitted development providing that they do not exceed a certain size, classed as 50% of the available curtilage of the dwellinghouse, not including the original house itself.
The total footprint of all buildings (including extensions and outbuildings)cannot be more than 50% of the available curtilage of the dwellinghouse, not including the ‘original house’ itself. (See the previous post here for the definition of the ‘original house’).
In simple, practical terms; the total area of the property boundary, minus the footprint of the original house is 100% of the available area. Any additional extensions or outbuildings must not exceed a total of 50% of this available area.
It should be noted that whilst this excludes the area covered by the original house, any extensions or outbuilding constructed by previous owners are included as part of this calculation.
Height Restrictions
Maximum height restrictions
The highest part of the extension must not exceed the height of the highest part of the roof of the original house. For most properties this is either the highest ridge line, or the top surface of any flat roof (parapets, chimneys and other small protrusions are not included).
Maximum eaves heights
The eaves of the new extension should be no higher than the existing house. If the eaves are of different heights then the restriction is to the highest level of the eaves of the existing house. Additionally, if the ground is sloped then the eaves of the existing house are considered in elevation all the way around, and cannot be exceeded.
How to measure eaves heights
The heights of the eaves are measured where the upper surface of any roof (flat or pitched) meets the external wall. This doesn’t include any parapets or roof overhangs.
Boundary conditions and materials
Eaves heights: the 2m rule
If the extension falls within 2m of the property boundary at any point then the maximum eaves height must be 3m or below. If a new extension joins an existing one the two are considered holistically, with the rule applying to both parts.
Extending at the front of the house
Any extensions must not extend past the principal elevation, usually the front, of the original house. For these purposes the principal elevation is the side of the house that faces, either directly or at an angle, the main highway that serves the house. An invisible line is drawn across this face, extending to the boundary at either side which no new enlargement can exceed. If the principal elevation is staggered then this invisible line staggers along with it.
Materials
The materials that form the exterior of the extension must be of a similar appearance to those used in the construction of the existing house. This is to ensure that the extension is sympathetic to the existing building. This does not mean that materials need to be the same but that they need to minimise visual impact and to create a similar visual appearance. This condition creates some scope for subjectivity and therefore it is always best to consult with a professional or local authority if you are unsure whether the proposed materials would be deemed controversial.
Single storey rear extensions
How big can they be?
The permitted size of a rear extension is dependent on the property and the type of approval sought.
Under permitted development the maximum distance an extension can extend from the rear wall of the original house is 4m for a detached house and 3m for any other house. In both instances the maximum height of the extension is 4m. Extensions larger than this are subject to prior approval.
Prior approval extensions
As long as the property is not in a designated area the maximum distance from the rear wall of the original house may be increased to 8m for detached houses and 6m for any other house. However, a prior approval application has to be made to the local authority before any works commence. An extension of this size will also be subject to a neighbour consultation scheme.
Extending beyond an existing extension
If a new extension is made to an existing extension then the whole enlargement over the original house is considered holistically with the limitations applying to both elements jointly.
Stepped rear wall
If the rear of the house is staggered then the maximum extension distances apply to each rear wall independently.
Two storey rear extensions
Two storey extensions are permitted providing that they:
- Extend no more than 3m from the rear wall of the original house
- Are a minimum distance of 7m from the boundary opposite the rear wall of the house
It should be noted that these restrictions apply to the whole enlargement. For example, if a second storey is added to an existing single storey extension that is 4m deep, then the whole enlargement is treated as a two storey extension that exceeds the 3m restriction and therefore would not qualify for permitted development.
Side extensions
Side extensions must:
- Be a single storey
- Not exceed 4m in height
- Not exceed a width greater than half the width of the original house
If the width of the original house varies due to stepped walls then the width is considered as the widest point.
Infill Extensions
Extensions filling a gap between a side wall and a rear wall are permitted provided that they satisfy the criteria for both rear and side extensions simultaneously.
Which extensions are not covered under permitted development?
‘Wraparound’ extensions
Wraparound extensions are joint side and rear extensions that ‘wrap’ the external walls of the house. These types of extensions are often a great solution for opening up small and dark kitchen areas at the rear of the house, or to create a large open plan space.
However these types of extension are not covered by permitted development and will always require a planning application.
This is due to the fact that the whole enlargement is considered holistically. The ‘rear’ portion of the extension in any wraparound extension also extends past the side of the house, resulting in a side extension that will equal more than half the width of the original house. This restriction still applies even if the extensions are undertaken independently of one another.
Roof Terraces
Any extensions that include a provision of a roof terrace will always require planning permission. No roof terraces, or platforms above 0.3m are allowed under permitted development. This is due to the potential overlooking issues of neighbouring properties that may arise.
Summary
Whilst most of the restrictions are fairly straightforward they are largely demonstrated in isolation by the technical guidance. In practice most projects need to satisfy these criteria simultaneously. For an easier comparison of the restrictions you can download a summary infographic here.
If you are still unsure whether your project fulfills the criteria for extensions under permitted development above then please get in touch, we’d love to hear from you and to help in any way that we can.