Planning Permission Checker
Answer a few quick questions and find out whether your project needs planning permission — or whether you can go ahead without applying.
Summary: In London, whether you need planning permission depends on your property type, what you're building, and where you are. Flats always need it. Houses get more flexibility — but inner-London boroughs often have tighter local rules that remove the automatic permissions that apply elsewhere in England. This tool steps through the key questions to give you a starting position, in plain English.
What "automatic planning permission" actually means
In the UK, certain types of home improvement are automatically allowed without you having to apply to the council. The government has pre-approved them — as long as your project stays within set limits (size, height, distance from boundaries), you can go ahead. Architects call this "permitted development."
For a typical London house, the main works that are automatically allowed include:
- Single-storey rear extensions — up to 3 metres from the back of the original house for a terrace or semi-detached, 4 metres for a detached. A "bigger extension" scheme allows up to 6m/8m with a simpler notification process to the council.
- Rear dormer loft conversions — usually allowed if the dormer is at the back of the house (not facing the road) and adds less than 40m³ (terrace) or 50m³ (semi/detached) to the roof volume.
- Rooflight / Velux conversions — generally allowed, provided rooflights on the front slope don't stick out more than 150mm above the roof plane.
- Garden rooms and outbuildings — allowed if single-storey, under 4m high, and covering less than half the garden area.
- Garage conversions — converting an attached garage into a habitable room is usually allowed without planning.
Projects that always need a planning application include two-storey extensions, mansard and hip-to-gable roof conversions, new builds, annexes, and all external works to flats.
Why some London properties have extra restrictions
Many inner-London councils — including Islington, Hackney, Camden, Lambeth, Southwark, and parts of Lewisham and Wandsworth — have used special council orders to remove some of the automatic planning permissions that apply elsewhere in England.
The effect is that a rear extension which would be automatically allowed in Bromley or Richmond requires a full planning application in Islington or Hackney. The council's planning portal will tell you whether these restrictions apply to your address. If you're in an inner-London borough, it's always worth a quick check before assuming you don't need to apply.
Conservation areas also carry extra rules — the council has more say over the materials, style, and visibility of any changes you make to the building.
Do you need a certificate even if planning isn't required?
If your project doesn't need a planning application, you can still apply to the council for a formal certificate confirming the work is lawful (called a Lawful Development Certificate). It costs around £206 and takes about 8 weeks.
This is strongly recommended. Without it, when you come to sell your home, the buyer's solicitor will ask for evidence that the work was done legally. A certificate makes that straightforward. Without one, you may end up commissioning a retrospective report or indemnity insurance — both more expensive and less clean than getting the certificate at the time.
What happens if you build without the right permission
If you carry out work that needed planning permission and didn't get it, the council can issue an order requiring you to undo the work. They have four years to do this for most types of building work. This can be a very costly problem — and it will surface when you come to sell, because solicitors will check.
The risk isn't just theoretical. Unauthorised work is a common reason property sales fall through or are delayed. Getting the planning position right upfront — even if that means a few weeks for a council certificate — is almost always worth it.
Common London projects and whether they typically need planning permission
| Project | House (typical) | Flat |
|---|---|---|
| Single-storey rear extension (within depth limits) | No planning needed | Planning required |
| Single-storey rear extension (beyond standard limits) | Notify council — simpler process | Planning required |
| Two-storey rear extension | Planning required | Planning required |
| Wrap-around extension | Planning required | Planning required |
| Rear dormer loft conversion | Usually no planning needed | Planning required |
| Hip-to-gable loft conversion | Planning required | Planning required |
| Mansard conversion | Planning required | Planning required |
| Garage conversion | Usually no planning needed | Check with council |
| Garden room / outbuilding | Usually no planning needed | Planning required |
| Any work to a listed building | Historic building consent required | Historic building consent required |
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By My Local London Builder Team · Last updated May 2026 · Guidance only, not a planning determination.