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What size extension can I build without planning permission?

In many circumstances, rules known as ‘permitted development’ rights allow you to extend a house without needing to apply for planning permission, providing specific limitations and conditions are met. If you want to exceed these limits and conditions, then it is likely that an application for householder planning permission will be required.

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You can find information about the limits and conditions, prior approval and the building regulations on the Planning Portal by using the links below.  

Read about planning permission for extensions

Read about prior approval for larger single storey extensions

Find out about building regulations for an extension

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Common Questions

Do I need permission to remove chimney stack on a property in a conservation area?

Removing a chimney stack may fall under permitted development rights, meaning no application for planning permission is required provided certain limits and conditions are met.

The permitted development right which covers this focuses on the installation, alteration or replacement of a chimney, note that this does not specifically mention removal. Rules in a conservation area may differ, in this instance you should contact your local planning authority directly to understand their position, and if the building is listed, then you will need listed building consent.

To ensure that the local planning authority will allow the removal of the chimney stack you can apply for a lawful development certificate. If approved, then no enforcement action can be taken against the change.

If the chimney is shared (i.e. as part of a terrace), you might need to discuss with relevant neighbour and obtain a party wall agreement.

Building regulations approval may not be required if you are removing the external chimney stack above the roof. If works progress to the internal chimney stack or breasts, then it will require building regulations to understand the structural impact.

Read more about planning and building regulations on Planning Portal.

What is an improvement notice?

An improvement notice is a notice served by a local authority requiring a property owner to carry out specified works to bring a building into compliance with the legal standards. These are most commonly served to landlords to make a building safe.

The notice will specify what works should be completed and when it should begin and be completed by.

Failure to comply with an improvement notice is a criminal offence.

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What is a listed building?

A 'listed building' is a building, object or structure in the UK that has been considered as of national importance in terms of architectural or historic interest and included on a register called the List of Buildings of Special Architectural or Historic Interest.

Buildings are listed to help protect the physical evidence of our past, including buildings, which are valued and protected as a central part of our cultural heritage and our sense of identity. Historic buildings also add to the quality of our lives, being an important aspect of the character and appearance of our towns, villages, and countryside.

There are three listing grades:

- Grade I - Buildings of exceptional interest

- Grade II* - Particularly important and more than special interest

- Grade II - Buildings of special interest, warranting every effort being made to preserve them (this is the most common)

If you live in a listed building it means you cannot demolish or alter the building in a way that changes its character without Listed Building Consent.

Read detailed guidance on Listed Building Consent

Do summerhouses or garden offices need building regulations approval?

If you plan to put up a small, detached building like a garden shed, garden room, garden office, annexe or summerhouse (all classed as outbuildings), building regulations generally won’t apply if the building has a floor area under 15 square metres and does not include any sleeping accommodation.

For buildings with a floor area between 15 and 30 square metres, building regulations approval is usually not needed - as long as the building does not include sleeping accommodation and either:

  • it is at least one metre away from any boundary, or
  • it is built mainly from non-combustible materials.

Read more about the building regulations that apply to outbuildings.

Don't forget to check the permitted development rights for outbuildings.

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Do I need building regulations approval to add underfloor heating?

Whether you need building regulations approval depends on the type of underfloor heating (UFH) you are installing.

Electric UFH must comply with Part P for electrical safety.This work can be done by a member of the competent persons scheme who can self-certify the work.

Wet UFH must comply with Part L which focuses on the conservation of fuel and power. This will likely require building control approval.

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