A rear extension can provide valuable additional living space by extending a home into its garden. In England, certain rear extensions can be built under permitted development rights without submitting a full planning application. However, strict rules apply to the extension’s size, height, position and design. Understanding these requirements before starting work can help you establish whether your proposed rear extension qualifies as permitted development or whether planning permission is required.
Can a Rear Extension Be Permitted Development?
A rear extension can qualify for permitted development under Class A of the householder permitted development rights, provided it satisfies all the relevant conditions and limitations. These rights apply to houses, but not generally to flats, maisonettes or other buildings. For a standard single-storey rear extension, the extension can generally project up to 4 metres from the rear wall of a detached house or 3 metres from the rear wall of any other house. Larger single-storey rear extensions may be possible under the neighbour consultation scheme, allowing up to 8 metres for detached houses or 6 metres for other houses, subject to the relevant requirements. Other restrictions can also apply, including rules concerning height, boundaries, site coverage, materials and the property’s location.
Key Permitted Development Rules for Rear Extensions
Maximum Depth
The maximum depth of a permitted development rear extension depends on the type of property. For a detached house, a standard single-storey rear extension can extend up to 4 metres beyond the rear wall of the original house. For a semi-detached or terraced house, the standard limit is 3 metres. Larger single-storey rear extensions may be permitted up to 8 metres for detached houses and 6 metres for other houses, provided the property is not on certain designated land or a Site of Special Scientific Interest and the neighbour consultation requirements are satisfied. The measurement is taken from the rear wall of the original dwellinghouse, so previous extensions can affect the amount of additional space available.
Maximum Height
A permitted development single-storey rear extension must not exceed 4 metres in height. Where the extension comes within 2 metres of the boundary, its eaves height must not exceed 3 metres. These restrictions should be considered carefully when designing the roof, particularly where the garden slopes or the extension is close to a neighbouring boundary.
Where Can a Rear Extension Be Built?
Permitted development rules restrict extensions from projecting forward of the principal elevation of the original house. Where a proposed extension also affects a side elevation, the restrictions that apply to side extensions may need to be considered as well.
This is particularly important for properties with unusual layouts or stepped rear walls. The position of the original house, existing extensions, boundaries and neighbouring properties should all be considered before determining the maximum size of the proposed extension.
Other Conditions for Rear Extensions
Meeting the permitted depth and height limits does not automatically make a rear extension permitted development. Other Class A conditions must also be satisfied. For example, the total area of ground covered by buildings within the curtilage, excluding the original house, must not exceed 50% of the total area of the curtilage. Existing extensions, garages and other buildings may therefore need to be included in the calculation.
The extension must also not be higher than the highest part of the existing roof, and exterior materials should generally have a similar appearance to those used on the existing house. Permitted development rights also do not allow verandas, balconies or raised platforms as part of the extension.
Can a Two-Storey Rear Extension Be Permitted Development?
Certain two-storey rear extensions can qualify for permitted development, but they are subject to stricter conditions. A two-storey extension must generally not extend more than 3 metres beyond the rear wall of the original house and must be at least 7 metres from any boundary opposite the rear wall. Additional requirements can apply to roof design and upper-floor windows. Because two-storey extensions involve more complex restrictions, the proposed design should be assessed carefully before relying on permitted development rights.
Larger Rear Extensions and Prior Approval
The larger home extension provisions can allow a single-storey rear extension to project further than the standard permitted development limits. However, these larger extensions are subject to a neighbour consultation scheme. For a detached house, the extension can generally extend up to 8 metres from the original rear wall, while other houses can generally extend up to 6 metres. The local planning authority must be notified and adjoining neighbours given an opportunity to comment. This means that a larger rear extension is not simply exempt from the planning process. The correct prior approval procedure must be followed before construction begins.
Rear Extensions on Designated Land
Additional restrictions apply to rear extensions on certain protected land. Article 2(3) designated land includes conservation areas, national parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites. Standard permitted development rights are more restricted in these locations. For example, larger single-storey rear extensions under the neighbour consultation provisions are not available in the same way, and additional restrictions apply to certain two-storey rear extensions and external alterations. An Article 4 Direction can also remove or restrict permitted development rights in particular locations. Planning conditions attached to an earlier permission may have a similar effect.
Do Rear Extensions Need Building Regulations Approval?
Planning permission and building regulations are separate requirements. Even where a rear extension qualifies as permitted development, the construction will normally need to comply with applicable building regulations. These requirements can cover structural stability, foundations, insulation, ventilation, fire safety, drainage and other technical matters. It is therefore important to consider both planning and building control requirements when developing the design. Permitted development rights do not remove the need to comply with other legal requirements.
Common Rear Extension Planning Mistakes to Avoid
A common mistake is assuming that any single-storey extension at the back of a house automatically qualifies as permitted development. The rules contain several requirements that must be satisfied together. Other common issues include:
- Measuring the extension from the wrong part of the house.
- Exceeding the permitted depth.
- Ignoring the 3-metre eaves restriction near boundaries.
- Failing to account for previous extensions.
- Overlooking the 50% site coverage requirement.
- Assuming a larger rear extension does not require prior approval.
- Failing to check conservation area or Article 4 restrictions.
- Assuming permitted development removes the need for building regulations approval.
Getting the measurements or planning position wrong can result in enforcement problems and potentially expensive alterations.
Should You Apply for a Lawful Development Certificate?
If your proposed rear extension appears to comply with permitted development requirements, you can apply for a Lawful Development Certificate to obtain formal confirmation from the local planning authority. An LDC is not planning permission. Instead, it confirms that the proposed or existing development is lawful for planning purposes.
Although an LDC is not always compulsory, it can provide useful evidence of the planning status of the extension, particularly when selling or remortgaging the property. Government guidance also confirms that homeowners can apply for an LDC where they want certainty that the proposed development is lawful.
How Studio Charrette Can Support Your Rear Extension Project
Studio Charrette planning services can help homeowners establish whether a proposed rear extension is likely to qualify for permitted development or whether a planning application is required. Our team can assist with planning assessments, architectural design, drawings and planning applications, helping you understand the restrictions that apply to your property before construction begins.
For projects involving previous extensions, unusual layouts, boundary constraints or potential planning restrictions, professional advice can help identify issues at an early stage and avoid unnecessary costs.
Planning Your Rear Extension
A rear extension can often be developed under permitted development rights, but only where the relevant conditions are satisfied. The most important requirements include the permitted depth and height, the property’s type, boundary distances, site coverage and the location of the property. Larger rear extensions may benefit from increased permitted development limits but are subject to the neighbour consultation scheme and other requirements. Where the project falls outside permitted development rights, a householder planning application may provide the appropriate route.
Before starting work, it is advisable to check the planning position carefully and ensure that the proposed design complies with all relevant requirements. If you need advice on your proposed rear extension, contact Studio Charrette for professional planning and architectural support.
Frequently Asked Questions
Can I build a rear extension without planning permission?
Yes, a rear extension may be permitted development if it satisfies the relevant Class A conditions. The permitted depth, height, location, site coverage and other requirements must all be considered.
How high can a rear extension be?
A single-storey rear extension can generally be up to 4 metres high. Where the extension is within 2 metres of the boundary, its eaves height must not exceed 3 metres.
Can I build a two-storey rear extension under permitted development?
Certain two-storey rear extensions can qualify for permitted development, but they are subject to stricter requirements, including a maximum projection of 3 metres beyond the original rear wall and a 7-metre boundary restriction.
Do larger rear extensions need prior approval?
Yes. Larger single-storey rear extensions that exceed the standard depth limits are subject to the neighbour consultation scheme, which involves notifying the local planning authority and adjoining neighbours.
