Planning · Extensions
Do I need planning permission for an extension?
Most single-storey rear extensions fall under permitted development — but not on flats, not in conservation areas, and not where an Article 4 direction applies.
The short answer
Many single-storey rear extensions do not need a planning application, because they fall under permitted development rights granted nationally. A single-storey rear extension can extend up to 3 metres beyond the original rear wall on a terraced or semi-detached house, or 4 metres on a detached house, with a maximum height of 4 metres.
Where the extension comes within two metres of a boundary, the eaves height is capped at 3 metres. The extension must also be built in materials of similar appearance to the existing house, and it cannot extend beyond a side elevation that fronts a highway.
The larger home extension scheme
Depths of up to 6 metres (attached) and 8 metres (detached) are possible under the Larger Home Extension scheme, which was made permanent in 2019. This is not automatic permitted development: it requires a prior approval application to the council.
Under prior approval, the council notifies your adjoining neighbours and gives them a consultation period to object. If nobody objects, the council cannot refuse on amenity grounds. If someone does, the council assesses the impact on their light and outlook and decides.
It is faster and cheaper than a full planning application, but it is a real application with a real timetable — build it into the programme rather than assuming you can start next month.
When permitted development does not apply at all
Flats and maisonettes have no permitted development rights whatsoever. Any external alteration to a flat needs a planning application, and almost certainly the freeholder's consent as well.
In a conservation area, permitted development rights are restricted — side extensions and cladding in particular. Where the council has made an Article 4 direction, rights can be removed entirely for the streets it covers, and those directions vary street by street within a borough.
Listed buildings are a separate regime again: listed building consent is required for alterations, and it applies to internal work as well as external.
Permission is not the same as approval to build
Planning permission and Building Regulations are two different systems, and you generally need to satisfy both. Planning is about what the building looks like and how it affects neighbours; Building Regulations are about whether it is structurally sound, insulated, safe in a fire, and properly drained.
Even a permitted development extension needs building control. Part A covers structure, Part L insulation and airtightness, Part K any change in level, and Part P the electrical work. Building control inspects at stages — including before foundations are covered over, which is the one people most often miss.
This guide describes national rules for England and was written to be accurate at the time of publication. Local designations can restrict them further, and legislation changes. Always confirm the position for your own address with your local planning authority, or ask us to do it in writing.
Related service: Extensions in London
Answers
Questions we get asked alongside this
Do I need planning permission for extensions in London?
It depends on the property type and what is proposed. Many single-storey rear extensions and loft conversions fall under permitted development, but those rights do not apply to flats and are restricted in conservation areas or where an Article 4 direction applies. We check the planning position for your specific address before quoting, and tell you in writing which route applies.
How do you price the work?
From a site survey, written up as a fixed and itemised scope before any deposit is discussed. If something genuinely unforeseen appears once work is opened up, it is priced and agreed in writing before we continue — never added to the final invoice after the fact.
When do I pay?
In arrears of work completed. You pay for work that has been done and inspected, not for work that has been promised. This has been how the company operates since 2008.
Do you handle Party Wall notices?
Yes, where the work requires them. Under the Party Wall etc. Act 1996, notifiable work on a shared wall needs 2 months written notice to the adjoining owner, while excavation near a neighbouring structure and building at the line of junction need 1 month. We serve the notices and manage the award process as part of the job.
Will I get certificates at the end?
Yes. Electrical work is tested and certificated under Part P, and building control issues a completion certificate where an application was required. You receive the handover pack — it is what a buyer's solicitor will ask for when you eventually sell.
How long will it take?
It depends entirely on scope, and we give a programme with the written quote rather than a guess on the phone. What we will not do is start a job we cannot resource, which is the usual reason a build stalls halfway through.
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