How Far Can I Extend My House Without Planning Permission?

If you live in a flat, permitted development rights do not apply, even if your home is on the ground floor. Homeowners who live in apartments cannot build extensions without planning permission – this exception only applies to houses.

Houses can also be ineligible for permitted development if they have been converted already. This depends on the nature and size of the conversion.

For example, if your home already has an extension built since 1948, you sometimes cannot use permitted development twice. However, your local planning office can confirm whether this applies to your property.

Listed buildings and homes in conservation areas must comply with different sets of rules that determine the changes you are allowed to make to your property.

Permitted development does not apply to any listed building or protected areas. You cannot construct a side extension, build to the rear above one storey or install exterior cladding. Other works may be allowed, but you must verify this according to the listed building terms and restrictions.

What Are the Permitted Development Rules for Home Extensions?

Front extensions almost always require planning permission because they affect the frontage of the property and any public roads, pavements or buildings in front of your home.

Side extensions must comply with the following requirements to be eligible for permitted development:

  • No more than half as wide as the original house.
  • No more than three metres away from the property.
  • Not facing a road.

Single-storey extensions can be up to eight metres for a detached house or six metres for other property types. If the extension is over four metres, you must notify your neighbours and ensure there are no objections.

Double-story treat extensions can extend out by up to three metres. They must not be within seven metres of the property boundary, with a roof shape that matches the existing one, and side windows at least 1.7 metres higher than the floor level.

All extensions that qualify for permitted development cannot have a balcony, raised deck or veranda.

House Extension Rules for Terraced and Semi-Detached Houses

Under permitted development, you can extend up to three metres without planning permission, applicable to terraced and semi-detached houses.

You should apply for a lawful development certificate either before or after the work is completed. It is advisable to apply before, as the document acts as evidence that you have received confirmation from the planning office that your extension qualifies as a permitted development.

If you sell your property in the future, you can pass on the certificate to verify the legality of your extension.

It is worth consulting your local planning authority, an architect or an experienced contractor if you have any concerns about your planning permission requirements. It can be extremely costly to rectify work if you have not applied for the right consent and need to make alterations.

Full planning permission is mandatory if you live in a conservation area. It may also apply if you wish to build an extension with different materials than those used in your original property.

Planning officers use a rule called the 45-degree rule. If they draw a line at 45 degrees from your neighbour’s nearest living space, this should not be overlooked by your extension. If the new structure impacts access to light on neighbouring properties, you may also need full permission.

Extension Rules for Detached Houses

The permitted development rules vary for detached houses and allow you to build an extension of up to four metres or up to eight metres if you have prior approval or qualify for the larger home extensions scheme.

Several factors impact eligibility for permitted development, so even if the dimensions of your planned extension seem to qualify, it is worth confirming this with an experienced professional.

As with other property types, you must apply for full planning permission if you live in a designated area, conservation zone or listed building managed by Heritage England.

You are more likely to be able to build a larger extension if you have a detached property with a relatively large garden. The rules look at the proximity of the neighbouring properties, how close your extension is to the boundary and whether it impacts public highways. Hence, size is only one of the variables.

How Difficult is it to Get Planning Permission for an Extension?

If you do not qualify for permitted development, you can proceed with a full planning application and open up opportunities to increase the size of your extension or use alternative materials and finishes.

The costs vary between UK regions but are around £206.

You should also budget for the associated services, which tend to be around £1,000 – £2,000, including the costs of technical drawings and conducting surveys which the local authority will need to review alongside your application document.

It usually takes approximately eight weeks to hear back from the planning office, and the consent is valid for up to three years unless other conditions apply.

Professionally drawn plans and detailed designs make approval more likely, so hiring a qualified architect or designer who will be familiar with the local planning rules is advisable.

Mike Alexander
Hey there, I'm Mike - writer and part time home improvement expert at Refurbb. Since owning and refurbishing my own property in 2018, I've since been developing rental properties, writing about my home improvement endeavours, sharing what I've learned and connecting readers to reputable tradespeople in the UK.

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