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What do I need to know about new foundations for an extension?

Foundations are required to carry and distribute the load of the building safely. Therefore, all buildings should have adequate foundations. The factors that need to be considered when designing a foundation are:

  • Type of soil
  • Adjacent structures
  • Trees
  • Drains and sewers
  • Size and construction of the new building
  • Ground condition
  • Landfill sites

It is advisable to contact a structural engineer or speak to a building control body about plans for new foundations. 

Read more about foundations for extensions.

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.

Do I need planning permission to add a first-floor extension onto an existing ground floor extension?

Adding a storey on top of an extension will always require an application for planning permission.

If you want to add a storey on top of your house under permitted development rights, it must be on the principal part of the house.

If you want to add an additional storey on top of your house, it can be permitted development. It is only permitted development if it follows certain rules:

The current house

  • Is not a building containing one or more flats, or a flat contained within such a building
  • Was constructed between 1 July 1948 and 28 October 2018
  • Has not already had additional storeys added to it
  • Is not on Article 2(3) land or a site of special scientific interest
  • Was not changed to be used as a house (from a previous non-residential use) under permitted development rights.

How many storeys can you add?

  • If the house is one storey then one storey can be added
  • If the house is two or more storeys then two storeys can be added

Where can the storeys be added?

  • The additional storeys must be added to the principal part of the house. The principal part of the house is the main part of the house excluding any front, side or rear extension of a lower height (regardless of these being part of the original house or subsequent additions).
  • Engineering operations must only include works within the existing curtilage of the house to strengthen existing walls and foundations

How high can it be?

  • The house cannot exceed 18 metres in total height
  • Each storey cannot add more than 3.5 metres to the total height
  • If the house is not detached the total height cannot be more than 3.5 metres higher than the next highest building that the house is attached to, adjoins, or is in the same row as.
  • The additional storeys must have an internal floor-to-ceiling height of no more than 3 metres, and no greater than the internal height of any existing storey within the principal part of the house.

What materials can be used?

The materials used must be of a similar appearance to those used in the construction of the exterior of the current house

Where can windows be placed?

Windows must not be placed in any wall or roof slope forming a side elevation of the house.

Following completion of development:

  • The house must remain in use as a domestic residential property
  • No visible support structures must remain on or attached to the exterior of the house
  • The roof pitch of the principal part of the house must be the same as it was prior to the development.

 If any of the limits set out above are exceeded then an application for planning permission will be required. If you are unsure, you should contact your local planning authority.

Find contact details for your local planning authority.

Do I need planning permission or building control approval to raise the height of an external doorway?

Whether raising the height of an external door requires planning permission depends on the location of the door, location of the property and how drastic the height change will be.

For smaller changes to the side and rear of the property, permitted development rights may apply, meaning no application or planning permission is required.

Where the height change will be substantial and have a significant impact on the building’s appearance, planning permission is likely to be required. Especially in cases where the door to be heightened is on the principal elevation of the property.

Principle elevation - The most visible or prominent side of a structure, typically facing a street or public area. While often considered the 'front' of the building, it may not always contain the main entrance.

In designated areas such as conservation areas, or on listed buildings you may require additional approvals such as listed building consent.

If you believe permitted development rights apply to a small change, you can apply for a lawful development certificate to ensure this is the case.

Building regulations

Building regulations approval will likely be required where the change impacts the structure of a building, this primarily occurs when an opening is widened. When altering walls you may want to consult a structural engineer.

Do I need planning permission to raise garden level?

Raising your garden level a small amount is likely to not require planning permission as it is likely to have minimal impact on the chances of flooding or overlooking your neighbours.

Increases of over 30cm may require planning permission as a significant change can impact drainage or your neighbours. If the changes are close to a boundary, you should consider whether it will overlook your neighbours or be intrusive.

You should contact your local planning authority to understand whether your proposed changes will require planning permission.

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