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Planning permission and building-regulations approval are separate checks. Planning law asks whether the extension may be developed on your property; building regulations ask whether the work is designed and constructed safely and to the required technical standards. An extension can be permitted development and still need building-regulations approval, and some projects need both formal planning permission and building control approval.
The permitted-development examples and thresholds below apply to England. If your home is in Wales, Scotland or Northern Ireland, use that nation’s rules and speak to the relevant local authority before relying on any English threshold.
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The two approvals answer different questions
GOV.UK describes the distinction plainly: “Building regulations approval is different from planning permission. You might need both.” Treating one approval as a substitute for the other is the most common regulatory mistake on an extension project.
| Issue | Planning permission | Building regulations |
|---|---|---|
| What it controls | Whether the proposed development is acceptable under planning law, including its scale, position, appearance and effect on the surrounding area. | How the extension is designed and built, including structural safety, fire safety, ventilation, drainage, energy performance and other technical requirements in the Building Regulations 2010. |
| Typical legal trigger | Building operations and structural alterations fall within the statutory meaning of “development”. Some householder work is exempt from a planning application because permitted-development rights apply. | Construction and extensions are covered by the Building Regulations 2010. Certain alterations, such as some window and door replacements, roof-covering changes, heating, plumbing and electrical work, may also require approval. |
| Who deals with it | Your local planning authority, either through a planning application or a permitted-development process such as prior approval where applicable. | A local-authority building-control service or a private registered building control approver. A competent-person scheme can cover certain defined work. |
| What you receive | A planning permission, a prior-approval decision, or—if you need formal confirmation that work is permitted development—a lawful development certificate. | Building-control plans or inspection approval and, when the work is satisfactorily completed, compliance documentation. |
| What happens if you ignore it | The local authority can take planning-enforcement action where unauthorised development has occurred. | Prosecution and a fine are possible, and the building-control body can require defective work to be corrected. Missing compliance records can also complicate a later sale. |
Because the systems operate independently, obtain a clear answer on both before construction starts. A planning decision does not certify the structure, and a building-regulations approval does not grant planning permission.
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When an extension needs planning permission in England
GOV.UK says planning permission is needed when work meets the statutory definition of development. Building an extension is normally a building operation, so the starting assumption should be that planning law must be checked. The project may proceed without a full planning application only if it fits every applicable permitted-development limitation and condition.
Permitted development is conditional, not automatic
Householder permitted-development rights are set out in Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended. The technical guidance requires the proposal to satisfy all limitations and conditions under every class that applies. An extension can engage more than one class; for example, an addition connected to the main roof may also have to comply with roof-alteration rules.
Permitted development is therefore a property-specific design test. The fact that a neighbour built an extension, or that a drawing is within a headline depth, does not prove that your proposal qualifies.
Common single-storey rear-extension dimensions
For an eligible ordinary single-storey rear extension in England, the commonly used limits are:
| House type or route | Maximum projection beyond the original rear wall | Height limit | Extra procedure |
|---|---|---|---|
| Detached house under the ordinary householder route | 4 metres | 4 metres | All other applicable limitations and conditions still apply. |
| Any other house under the ordinary householder route | 3 metres | 4 metres | All other applicable limitations and conditions still apply. |
| Eligible larger single-storey rear-extension route | Up to 8 metres for a detached house or 6 metres for another house | Subject to the applicable permitted-development conditions | Neighbour-consultation and prior-approval procedure applies. |
These are technical thresholds, not a complete permission test. The detailed permitted-development guidance cited here was last updated on 10 September 2019, while the underlying order has been amended. Check the current legislation and your local authority’s procedure before relying on a measurement.
What else must be checked
The permitted-development assessment also considers matters that are easy to miss on a tape measure:
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- The extension’s height, width, roof form and relationship to the original house.
- How far the addition projects beyond each original rear wall, including where the house has an unusual or staggered plan.
- Distance from boundaries and the separate restrictions that apply to side extensions.
- Existing additions and enlargements. Joined or cumulative enlargements can count together rather than being assessed as isolated projects.
- The total area of the curtilage covered by buildings other than the original house, which must not exceed 50%.
- The requirement that an extension must not exceed the highest part of the existing roof, together with applicable roof and eaves conditions.
- The type of property and whether it is a house to which the householder rights apply.
Read the relevant class as a set of conditions. Failing one condition can remove the permitted-development route even when all the headline dimensions appear acceptable.
Protected locations and restrictions that can remove permitted development
Article 2(3) land
National Parks, the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites are identified in the guidance as article 2(3) land for relevant additional limitations. A design that would be permitted development elsewhere may be restricted in one of these locations.
Article 4 directions
A local planning authority can use an Article 4 direction to remove specified permitted-development rights in a defined area. The existence and scope of a direction must be checked for your property, not inferred from a general statement about the town or postcode.
Earlier planning permissions and property records
An earlier permission may have removed or narrowed permitted-development rights through its conditions. Look at the original house permission, subsequent applications and the local planning authority’s property-specific records. Extensions already built may also affect the calculation of cumulative enlargement or the remaining curtilage.
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For an eligible larger rear extension, the neighbour-consultation scheme requires the homeowner to notify the local planning authority. The authority gives adjoining neighbours an opportunity to comment and then decides whether prior approval is required.
Under the technical guidance, work must not commence until the authority says prior approval is not required, grants prior approval, or 42 days pass without a decision. Confirm the current notice, plans, fee and timing requirements with your local authority before treating the 42-day period as permission to start. A neighbour’s lack of objection is not itself a building-regulations approval or a guarantee that every permitted-development condition has been met.
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When building-regulations approval is needed
Building regulations apply to the construction of an extension even where planning permission is unnecessary. They address the performance and safety of the completed work rather than whether the development is acceptable in its location.
Work commonly considered by building control
- Foundations, load-bearing walls, beams, roof structure and connections to the existing building.
- Fire separation, escape considerations and the protection of any existing dwelling above or beside the work.
- Floors, insulation, energy performance, ventilation and prevention of condensation.
- Drainage, sanitary facilities and connections to existing services.
- Electrical, heating and plumbing elements where the regulations or another approval route applies.
- Alterations that are not an extension but are included in the building-regulations regime, such as some window and door replacements or roof-covering changes.
The exact submission and inspection requirements depend on the design and the work package. If you cannot establish the status of a particular alteration, GOV.UK advises researching that project or checking with a building-control body.
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Approval routes
For work that is not higher risk, you can normally use either your local authority’s building-control service or a private registered building control approver. Certain defined jobs may be self-certified through a competent-person scheme. Ask the chosen body which route covers each element before work begins; self-certification is limited to the scope of the person’s registration and does not replace planning permission.
Completion records matter
Keep the plans, notices, inspection records and completion certificate with the property documents. GOV.UK warns that without approval you may lack the compliance certificates requested during a sale. Non-compliant work can also lead to prosecution, a fine and a requirement to open up or rectify faulty construction.
Other consents that run alongside both systems
Party Wall Act
Permitted-development rights do not remove obligations under the Party Wall Act. The Act may be relevant to work on a party wall, at the boundary or near neighbouring foundations. It is a separate legal regime from planning and building control, so obtain project-specific advice and serve any required notices before the relevant work starts.
Other property-specific controls
Listed-building controls, restrictive covenants, lease terms, drainage-owner requirements and utility consents can also affect an extension. The planning and building-regulations approvals described here do not override those obligations.
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A reliable order for deciding what you need
- Identify the nation and authority. Confirm that the property is in England if you are using the thresholds in this article, then identify the local planning authority and building-control options.
- Document the existing house. Measure the original rear walls, roof height, boundaries and existing additions. Gather earlier permissions and plans so cumulative work is not overlooked.
- Test the planning route. Compare the design with every relevant permitted-development class and condition. If any condition fails, prepare for a planning application rather than assuming a minor redesign will cure it.
- Check restrictions. Search for article 2(3) status, an Article 4 direction and conditions on earlier permissions. Ask the authority to confirm any property-specific restriction.
- Choose certainty where it is valuable. If you need formal evidence that planning permission was not required, apply to the local authority for a lawful development certificate. This is a planning-law document; it is not building-regulations approval.
- Confirm neighbour-consultation requirements. If using the larger single-storey route, submit the required notification and wait for the authority’s decision or the applicable period to expire before starting.
- Refer the design to building control. Submit plans or a building notice through the local authority or a registered building control approver, or confirm which elements a competent-person scheme can certify.
- Deal with separate consents. Establish whether the Party Wall Act or another property-specific regime applies and complete its notices or approvals.
- Build to the approved information and retain evidence. Notify inspections when required, resolve defects promptly and keep the completion documents.
Comparing two typical extension concepts
The following comparison shows why a planning shortcut cannot be selected from depth alone. Both concepts still require a building-regulations assessment.
| Check | Ordinary rear extension concept | Larger rear-extension concept |
|---|---|---|
| Planning route | Potentially permitted development if the house, location, dimensions and every condition qualify. | Potentially permitted development only through the eligible larger route and its conditions; otherwise a planning application may be needed. |
| Depth guide | Up to 4 metres for a detached house or 3 metres for another house. | Up to 8 metres for a detached house or 6 metres for another house in an eligible case. |
| Neighbour procedure | No larger-extension neighbour-consultation step solely because it is an ordinary route, but other legal obligations can still apply. | Local-authority notification and the prior-approval process, with the guidance allowing 42 days without a decision before work may commence. |
| Other planning checks | Curtilage coverage, roof height, boundary, side-extension, cumulative-extension, protected-area and Article 4 checks. | The same checks, plus the conditions attached to the larger route. |
| Building regulations | Separate approval or certification is still required where the construction work is within the regulations. | Separate approval or certification is still required where the construction work is within the regulations. |
| Party Wall Act | Check independently where the work affects a party wall, boundary or neighbouring foundations. | Check independently where the work affects a party wall, boundary or neighbouring foundations. |
Common mistakes and how to avoid them
“It is under the permitted-development depth, so we can start.”
Depth is only one condition. Recheck the original wall, roof height, boundary relationship, cumulative additions, curtilage coverage and local restrictions. Obtain a lawful development certificate if documentary certainty will matter to a lender or future buyer.
“Planning approval covers the structure.”
It does not. Send the construction design to building control and arrange inspections. Planning drawings may not contain the structural and technical information needed for compliance.
“No neighbour objected, so no approval is needed.”
Neighbour comments are only part of the larger-extension prior-approval process. They do not waive a planning condition, building regulations or the Party Wall Act.
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“The previous owner’s extension does not count.”
Existing and proposed joined enlargements can be assessed together, and earlier permissions may have changed the available rights. Include the entire planning history in the assessment.
“We can sort certificates out when we sell.”
Retrospective evidence can be difficult, and defective work may have to be opened up or corrected. Select the building-control route before construction, notify inspections and keep the final certificate.
Quick Recap
Decision checklist before work begins
- Have you confirmed that the English rules apply to your property?
- Have you identified the original house, original rear walls and all existing additions?
- Has every relevant permitted-development limitation and condition been checked?
- Have you searched for article 2(3) status, an Article 4 direction and conditions on earlier permissions?
- Do you need a planning application or a lawful development certificate?
- If using the larger rear-extension route, has the neighbour-consultation procedure been completed and has the applicable waiting period passed?
- Has a building-control body confirmed the submission, inspection and completion process?
- Have you checked Party Wall Act and any other property-specific consents?
- Are the approval documents and completion records stored with the house papers?
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