House extensions guidance

Check if you need permission

Some small changes are classed as permitted development. Larger changes need planning permission.

Use our householder enquiry form to check what permissions you need:

• planning permission
• listed building consent
• building warrant

You can also ask for pre‑application advice if you want help before you apply.

Before you design your extension

Think about:

• how much space you have around your home
• how close your neighbours are
• the shape and size of your roof
• the materials your home is built from
• where your windows look onto
• space for parking and bins
• how you will deal with surface water
• any trees or hedges that could be affected

You might not have permitted development rights if:

• your property is in a conservation area - Check conservation areas
• your property is a listed building or within the curtilage of one - Check listed buildings
• a condition on a previous planning permission removed your permitted development rights
• protected species such as bats may be present in your roof or walls. You must check before you start work
• some trees are protected by a Tree Preservation Order

Design rules you need to follow

Your extension must fit your home and the area.

As a general guide:

• the extension should be smaller than the main house
• do not block light into your neighbour’s home
• avoid windows that look directly into your neighbour’s rooms or garden
• keep enough garden space
• keep safe access and parking
• use materials that match or complement your house

Corner plots and streets with a strong character may need more careful design.

Drainage and flood risk

You must deal with drainage on your site. Extensions must be at least 6 metres from watercourses - Check flood information

Outbuildings, annexes, balconies and decking

These may also need permission and may need changes if they affect the privacy or amenity of neighbours.

Download full technical guidance

If you are an architect, designer or need full details, download our technical planning guidance.

The guidance includes:

• full design standards
• daylight and sunlight tests
• detailed roof and dormer rules
• access and parking rules
• drainage and tree requirements

Read our house extensions and other residential alterations guidance