Do I Need Planning Permission for a House Extension?
Understand when planning permission is required, when permitted development may apply and which design issues often lead to objections.
The essential position
Some house extensions need a planning application, while others can use householder permitted development rights. The answer depends on the original house, the full planning history, the position and dimensions of the extension, designated-land restrictions and any Article 4 direction or planning condition that has removed permitted development rights.
Key points
- Check the original house and every later addition before measuring limits.
- Confirm whether the proposal complies with every permitted development limitation and condition—not only its depth.
- Planning permission and Building Regulations are separate approvals.
- A Lawful Development Certificate is usually sensible where you intend to rely on permitted development.
1. Start with the original house and planning history
Permitted development limits are measured from the “original dwellinghouse”: the house as first built, or as it stood on 1 July 1948 if it was built earlier. Previous extensions count against the allowance even if they were completed by an earlier owner.
Before fixing a design, check the council planning register, the property’s title and any earlier approvals. A condition on an old permission can remove permitted development rights, and an Article 4 Direction can require a planning application for work that would normally be permitted.
- Record rear-wall, side-wall, eaves and ridge dimensions.
- Identify attached garages, historic additions and converted outbuildings.
- Check conservation-area, listed-building and Green Belt constraints.
2. When permitted development may apply
Class A of Part 1 of the General Permitted Development Order can cover certain rear and side extensions to houses in England. The proposal must satisfy all relevant limits on position, height, width, projection, materials and the amount of curtilage covered.
The larger-home-extension route can allow a single-storey rear projection of up to 6 metres for an attached house or 8 metres for a detached house, but it uses a prior-approval neighbour-consultation procedure. It is not an automatic permission and does not apply in every location.
- Standard rear limits are commonly 3 metres for an attached house and 4 metres for a detached house.
- Extensions within 2 metres of a boundary face tighter eaves-height control.
- Side extensions must be single storey and no wider than half the original house.
3. Why a planning application can be the better route
A design that falls outside permitted development can still be acceptable through a householder planning application. Planning officers normally consider scale, massing, character, materials, neighbour daylight, privacy, outlook, trees, parking and the effect on the street scene.
Trying to force a poor layout inside permitted development rules can produce less useful space. A planning-led option may create a better relationship between kitchen, dining, garden and circulation while still addressing the authority’s design guidance.
- Test more than one footprint before selecting the approval route.
- Use accurate contextual elevations and site sections where levels or neighbours are sensitive.
- Explain design decisions rather than relying on drawings alone on constrained sites.
4. What a robust submission should contain
A typical householder application includes the application form, ownership certificates, fee, location plan, block or site plan and accurate existing and proposed drawings. Councils can also require local-list information such as tree details, heritage information, flood evidence or ecology surveys.
For permitted development, drawings should explicitly demonstrate the legal tests. A proposed Lawful Development Certificate is determined on lawfulness rather than planning balance, so ambiguous dimensions or missing planning-history evidence can lead to refusal.
- Use consistent dimensions across plans, elevations and roof plans.
- Show adjoining properties, boundaries and relevant windows.
- Keep a written schedule explaining how each permitted development test is met.
Questions homeowners commonly ask
Can I build an extension without planning permission?
Possibly. Householder permitted development can cover qualifying works to a house, but every limitation and condition must be satisfied and local restrictions must be checked.
Does the 45-degree rule decide whether permission is needed?
No. The 45-degree approach is generally a planning-design tool used by some councils to assess neighbour daylight and outlook; it is not the legal test for permitted development.
Do I still need Building Regulations approval?
Usually yes. Planning controls land use and external impact, while Building Regulations cover structure, fire safety, energy, ventilation, drainage and other technical matters.
Should I obtain a Lawful Development Certificate?
It is not always compulsory, but it provides formal evidence that the proposal was lawful at the date of the application and can be valuable for construction, finance and resale.
Official guidance and further reading
Get project-specific advice.
Every property has a different planning history, physical context and technical risk. Start with a focused review before committing to work.