Permitted development vs full planning permission
Most UK homeowners want to know one thing first: do I need planning permission or not? In 2026 the answer for most extensions on standard freehold houses is still "not necessarily" — permitted development rights cover many single-storey rear extensions up to defined size limits, plus loft conversions within volume allowances.
But permitted development is not a free pass. It comes with strict criteria on size, height, materials, position relative to boundaries and the original house footprint. Get any of those wrong and the work is technically unlawful — which becomes a problem when you sell.
For larger extensions, double-storey extensions, properties in conservation areas, listed buildings, flats or maisonettes, and any property in an Article 4 direction area, full planning permission is normally required.
How permitted development limits work in 2026
For detached houses, the rear extension limit under permitted development is generally 4 metres deep (single storey) or 8 metres under the Larger Home Extension prior approval route. For semi-detached and terraced houses, those numbers are 3 metres and 6 metres respectively. Eaves must not exceed 3 metres in height where within 2 metres of a boundary.
Materials must be similar to the existing house. Side extensions cannot exceed 50% of the original house width. Total extensions (rear, side, outbuildings combined) cannot cover more than 50% of the original garden area surrounding the house.
Loft conversions under permitted development are subject to volume limits (40 m³ for terraced, 50 m³ for semi/detached), cannot project beyond the existing roof plane on the front elevation, and must use similar materials.
Why a Lawful Development Certificate is worth getting
Even if your project genuinely is permitted development, you should still apply for a Lawful Development Certificate (LDC) from your local council. An LDC is the council’s formal confirmation in writing that your specific project does not require planning permission.
That document does two things: it protects you against future enforcement action, and it provides a clean answer when you eventually sell the property. Without it, conveyancers routinely raise queries that delay sales by weeks.
LDC application fees are around £129 (half the cost of a full planning application) and the council has eight weeks to determine the application.
Conservation areas and Article 4 directions
If your property sits in a designated conservation area, many permitted development rights are restricted. Cladding, side extensions, rooflights on the principal elevation and chimney alterations typically require full planning consent regardless of size.
Article 4 directions go further. They allow local authorities to withdraw specific permitted development rights street-by-street or area-by-area. Many London boroughs operate Article 4 directions covering front extensions, dormers, hardstanding, basement excavations and even paint colours.
Before designing anything, the first check we run on every project is the council’s online planning constraints map. That tells us in 30 seconds what we are actually working with.
The full planning application process
When full planning permission is needed, expect a 13–18 week timeline from application submission to decision for most householder applications. Add another 4–8 weeks for pre-application advice if you choose to use it (often worth it on borderline schemes).
A standard planning submission needs: site location plan, block plan, existing and proposed floor plans, existing and proposed elevations, design and access statement (often), and the planning application form itself. Application fees for householder extensions are currently £258.
Where neighbours object, applications can be referred to planning committee rather than decided by officers — adding weeks and bringing real uncertainty. We always advise neighbour consultation before submission rather than waiting for it to happen formally.
Frequently asked questions
How long does planning permission take in 2026?
A standard householder planning application has a statutory 8-week determination period, but in practice 13–18 weeks is more realistic for most London boroughs given current caseloads.
What happens if I build without planning permission?
The council can issue an enforcement notice requiring the work to be altered or removed. After four years (for unauthorised building work) or ten years (for unauthorised change of use) the work may become immune from enforcement — but it remains unlawful and complicates sale.
Do I need party wall agreements as well?
If your work involves digging foundations within 3 metres of a neighbouring building, building on the line of junction, or working on a shared wall, the Party Wall etc. Act 1996 applies. This is separate from planning and is handled by a party wall surveyor.
Planning a project of your own?
Book a free project review with the RCB team. We will respond within one working day.