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Building a home extension can be a hugely worthwhile project. Not only can it add much-sought-after living space to a property, it can also add value and make a home stand out in a seriously competitive market.

While a successful home extension requires solid planning it does not always require planning permission. Permitted development rights can be sufficient to cover extensions of a certain size, subject to a number of constraints. If you run your plans by a local architectural designer or builder and take the time to familiarise yourself with local planning regulations, you could well find that planning permission will not be necessary for what you have in mind.

It is important to remember that there is no excuse for simply assuming that an extension will be permitted. Your local council would be well within its rights to force you to tear down your extension if it contravenes local regulations (then hand you a sizeable fine). Our advice is to play it safe and plan carefully, making sure that your Pros have applied for the required permissions before building work begins.

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How to build an extension without planning permission

While Planning Permission would usually be required to make a significant alteration to a property, permitted development rights can often allow extension work to occur as long as it abides by certain rules. Exactly what these rules are can vary depending on where you live, so it can be an excellent idea to check local planning laws before making solid plans for your extension. For example, there is currently a temporary increase in what is permitted for single storey extensions, provided they are completed by 30 May 2019.

You should keep in mind that the rules below only apply to houses. Policies are usually different for flats and maisonettes, as well as listed buildings, properties subject to planning conditions and dwellings created through change of use. 

If your home is located in a conservation area, an Area of Outstanding Natural Beauty, a World Heritage Site or the Broads, you will almost certainly require planning permission to make any significant changes.

Before we continue, it is worth noting down the following definitions:

  • Original house - This refers to how your property was originally built, or how it stood on 01/07/1948 if it was built before that time. It is important to know this, as previous residents at your property may have built extensions themselves.
  • Designated land - There are a number of protected areas in the UK which have much more strict rules on alterations made to properties. These include the Broads, Areas of Outstanding Natural Beauty, World Heritage Signs, conservation areas and national parks.

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Rules for extensions for houses

  • No extension may be higher than the highest part of the property’s roof.
  • Single-storey rear extensions may not extend beyond the rear wall of the original house by more than four meters for a detached house or three meters for an attached house.
  • This limit is increased to eight meters for a detached house or six meters for an attached house outside Sites of Special Scientific Interest or designated land (until 30 May 2019). These limits are subject to prior notification of your proposal to your Local Planning Authority, as well as the implementation of the neighbourhood consultation scheme. In other words, the project may still not be permitted.
  • Additions and other buildings may not cover more than half the area of land around the original house.
  • No extension may be forward of a principal elevation or side elevation fronting a highway.
  • Single storey rear extensions have a maximum height of four meters.
  • Extensions higher than one storey may not extend beyond the original house’s rear wall by more than three meters.
  • Side extensions must be single storey, with a maximum height of four meters and a width no larger than half that of the original house.
  • Two storey extensions may be no closer than seven meters to the property’s rear boundary.
  • An extension within two meters of the property boundary must have eaves no higher than three meters.
  • Eaves and ridges for an extension may be no higher than the existing house.
  • Extensions higher than one storey must have a roof pitch matching the existing house.
  • Extensions may have no verandas, raised platforms or balconies.
  • Any side-facing upper-floor windows must be obscure-glazed, with openings 1.7m above the floor.
  • Materials used for extensions must be similar in appearance to the existing house.

For houses on designated land the rules are more strict:

  • No permitted development for rear extensions higher than one storey.
  • No exterior cladding.
  • No side extensions.