Most London single-storey rear extensions can still be built under permitted development (PD) — but the exceptions are numerous, and getting the route wrong costs months of delay. This guide covers the four planning routes a London homeowner might take, when each applies, and the two documents you always want to walk away with.
The four planning routes
- Permitted Development (PD) — you don't submit an application, but you should still get a Lawful Development Certificate. Applies to most terraced and semi-detached houses not in a designated area.
- Prior Approval (larger single-storey extensions) — for rear extensions between 4m and 6m on a semi/detached, or 3–6m on a terrace. Neighbours are notified; council has 42 days to raise objections.
- Full Planning Permission — required in conservation areas, Article 4 zones, for flats, listed buildings, or any scheme exceeding PD limits (e.g. double-storey rear over 3m, side extensions over 4m eaves).
- Listed Building Consent — separate from planning; required for any works affecting the character of a listed property, inside or out.
Permitted development limits (single-storey rear, houses only)
- Depth: up to 3m from the original rear wall on a terrace/semi, up to 4m on a detached — without prior approval.
- Larger PD (prior approval): up to 6m on a terrace/semi, up to 8m on a detached.
- Eaves height: 3m within 2m of a boundary, otherwise 4m.
- Materials: similar in appearance to the existing house.
- No verandas, balconies or raised platforms.
- Total ground area covered by extensions must not exceed 50% of the original curtilage.
Double-storey rear extensions are permitted only in narrow circumstances (max 3m depth, at least 7m from the rear boundary), which rules out most London terraces. Assume you need full planning.
The Article 4 problem
Several London boroughs have made Article 4 Directions that remove some or all permitted development rights for houses in specific areas. This is the single biggest reason London extensions get refused unexpectedly. Common examples:
- Islington: Article 4 covers most of the borough for changes to façades and rear extensions above certain thresholds.
- Camden: multiple conservation area Article 4s, notably in Primrose Hill, Hampstead, Bloomsbury.
- Hackney: Article 4 on flats and HMO conversions; some conservation areas restrict rear extensions too.
- Kensington & Chelsea: near-blanket removal of PD across conservation areas.
- Westminster: extensive PD restrictions on both houses and flats.
Always check your council's Article 4 map before assuming PD applies. It takes ten minutes and saves months.
Conservation areas
Over 1,000 conservation areas cover parts of every London borough. In a conservation area, cladding materials, window styles, side extensions and rooflights facing a public highway all become subject to planning control even if the works themselves would otherwise be PD.
Get a Lawful Development Certificate — always
Even when your extension is genuinely PD, apply for a Lawful Development Certificate (LDC). It costs £129, takes 6–8 weeks, and produces a certificate confirming your council's view that the works are lawful. Without one:
- Your buyer's solicitor will raise it as an enquiry on sale, and may push for a retrospective LDC as a condition of exchange.
- You have no defence if a neighbour challenges the works after the fact.
- Some lenders decline mortgages on properties with unregularised extensions.
Typical London planning timelines
- Lawful Development Certificate: 6–8 weeks
- Householder planning application: 8 weeks statutory, often 10–14 in practice in Camden, Hackney, K&C
- Prior approval (larger single-storey): 42 days
- Full planning + conservation area consent: 10–16 weeks
- Planning appeal (if refused): 6–9 months for a written representations appeal
How to give yourself the best chance
- Engage a local planner early. Someone who has read your council's Local Plan and Design Guide will spot the show-stoppers on a first read of your drawings.
- Talk to your neighbours before submission. Objections from adjoining owners are the single most common reason for London refusals. A ten-minute conversation neutralises most of them.
- Pre-application advice. Most London councils offer paid pre-app for £250–£800. Well worth it for a marginal or ambitious scheme.
- Get the drawings right. Materials schedule, sections, side elevations and existing/proposed drawings that match plan-form. Half of refusals are for insufficient information, not bad design.
What to do if you're refused
Don't panic — most London refusals are recoverable. In order of speed and cost:
- Amend and resubmit within 12 months (fee-free). Address each refusal reason in writing.
- Householder appeal (Planning Inspectorate, written representations). Free to submit; 6–9 months to decision.
- Redesign to fit PD limits. Sometimes losing 300mm of depth is faster than fighting the refusal.