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. Work through the steps below in order; each one either confirms your route or sends you to the next.
Step 1 — Check your property's designations before you draw anything
Ten minutes here saves months later. Every check below is free and public. Do all five before your architect starts.
- Conservation area?10 min
Search your borough's planning map or 'conservation area' layer. If yes, side extensions, materials and visible rooflights come under control.
- Article 4 Direction in force?10 min
Borough Article 4 map. This is the single most common reason a London extension unexpectedly needs full planning.
- Listed building?5 min
Historic England National Heritage List. If listed, you need Listed Building Consent for anything affecting character, inside or out.
- Is it a house or a flat?1 min
Flats and maisonettes have no permitted development rights at all. Full planning always applies.
- Have PD rights already been used or removed?20 min
Check the planning history for the address — a previous owner's extension counts against your allowance, and a planning condition may have removed PD entirely.
- Tree Preservation Orders or root protection?10 min
A TPO'd tree near your foundation line changes the foundation design and the cost.
Step 2 — Identify your route
| Route | When it applies | Fee (2026) | Decision time |
|---|---|---|---|
| Permitted Development + LDC | Houses within PD limits, no Article 4, not listed, not a flat | £129 (LDC) | 6–8 weeks |
| Prior Approval (larger single-storey) | Rear 3–6 m on terrace/semi; 4–8 m detached | £120 | 42 days |
| Full Planning Permission | Conservation area, Article 4, flats, or beyond PD limits | £258 | 8 weeks statutory |
| Listed Building Consent | Any works affecting a listed building's character | No fee | 8 weeks, alongside planning |
Step 3 — Confirm you fit the PD limits
- Depth: up to 3 m from the original rear wall on a terrace or semi; 4 m detached.
- Larger PD via prior approval: up to 6 m terrace/semi, 8 m detached.
- Eaves: 3 m within 2 m of a boundary, otherwise 4 m; overall height max 4 m.
- Materials similar in appearance to the existing house.
- No verandas, balconies or raised platforms above 300 mm.
- Extensions must not cover more than 50% of the original curtilage.
- Side extensions: single-storey, max 4 m high, no wider than half the original house.
Double-storey rear extensions are PD only in narrow circumstances (max 3 m deep, 7 m clear to the rear boundary), which rules out most London terraces. Assume full planning.
PD + LDC route
Faster, lower risk, no neighbour consultation
- No design negotiation with a planning officer
- £129 and 6–8 weeks to a certificate
- Neighbours are not formally consulted
- Certificate satisfies solicitors on resale
- Design constrained to 3 m depth and PD envelope
Full planning route
Slower, but unlocks the scheme you actually want
- Depth, height and glazing driven by design, not rules
- Only route available for flats and listed buildings
- 21-day neighbour consultation with public objections
- 8 weeks statutory, 10–14 realistic in inner London
- Refusal is recoverable — free resubmission within 12 months
Step 4 — Build the drawing pack that gets validated first time
Roughly half of London refusals and delays are down to insufficient information, not bad design. Validation queues at busy boroughs add 2–3 weeks before the statutory clock starts, so an incomplete submission costs you a month.
- Site location planArchitect
1:1250, red line around the whole property, OS-based and licensed.
- Block planArchitect
1:200 or 1:500 showing the proposal footprint and boundaries.
- Existing plans, sections and all elevationsArchitect
1:50 or 1:100. Missing side elevations are the classic invalidation.
- Proposed plans, sections and all elevationsArchitect
Same scales, dimensioned depth and eaves height.
- Materials scheduleArchitect
Brick, mortar, glazing frame finish, roof covering, rainwater goods — named products, not 'to match'.
- Design and access statementArchitect
Required in conservation areas and for listed buildings; useful everywhere.
- Heritage statementConsultant
Conservation area or listed: how the proposal preserves or enhances character.
- Daylight / sunlight noteConsultant
Worth pre-empting where a rear extension flanks a neighbour's window.
- CIL additional information formYou
Submit with the application; late filing can trigger a surcharge even at £0 liability.
Step 5 — Talk to your neighbours before you submit
Objections from adjoining owners are the most common cause of London refusals. The conversation costs ten minutes and materially changes your odds.
- 1
Knock, don't post
2 weeks before submissionShow the drawings on paper at their kitchen table. People object to surprises far more than to extensions.
- 2
Name the two things they care about
Light and noiseBe specific about eaves height on the boundary and about working hours. Vague reassurance reads as evasion.
- 3
Offer the programme in writing
One pageStart date, duration, skip and scaffold weeks, and your mobile number. This single page prevents most objection letters.
- 4
Follow up after the consultation letter lands
Day 3–5Councils write to neighbours during the 21-day consultation. A short follow-up stops a neutral neighbour objecting out of caution.
Step 6 — Submit, then manage the determination window
Step 7 — Always get the paperwork that proves lawfulness
Even when your extension is genuinely PD, apply for a Lawful Development Certificate. Without one: your buyer's solicitor will raise it as an enquiry, you have no defence if a neighbour challenges the works, and some lenders decline mortgages on unregularised extensions.
If you are refused
| Option | Cost | Time | Best when |
|---|---|---|---|
| Amend and resubmit | Free within 12 months | 8–12 weeks | Refusal reasons are specific and fixable |
| Householder appeal | Free to submit | 6–9 months | Officer applied policy incorrectly and you have evidence |
| Redesign to PD limits | New drawings only | 6–8 weeks via LDC | Losing 300–600 mm of depth is acceptable |
| Pre-app then resubmit | £250–£800 | 12–16 weeks | Scheme is ambitious and you need the officer's steer in writing |
- Check Article 4 and conservation status before spending money on design
- Buy pre-application advice for any marginal or ambitious scheme
- Submit dimensioned drawings at stated scales, including every elevation
- Name real materials in the schedule
- Keep the decision notice, approved drawings and any LDC together for resale
- Assume PD because your neighbour built the same thing five years ago
- Measure depth from your current rear wall instead of the original one
- Submit without telling the adjoining owners first
- Start on site before the decision notice — retrospective is always more expensive
- Ignore planning conditions such as approved materials or obscure-glazing requirements
+Do I need planning permission for a 3 m rear extension in London?
On a house not in an Article 4 area or conservation area, a 3 m single-storey rear extension is usually permitted development. On a flat, in an Article 4 area, or where PD rights were removed by condition, you need full planning.
+How long does a London householder application really take?
Eight weeks is the statutory target. In Camden, Islington, Hackney and Kensington & Chelsea, 10–14 weeks is normal, plus 2–3 weeks of validation queue before the clock starts.
+Can a neighbour stop my extension?
They cannot veto it, but objections shape officer recommendations and can push a decision to committee. Planning weighs material considerations — loss of light, overlooking, character — not general opposition.
+What if I already built without permission?
Apply for retrospective planning or, if the works are over four years old and unchallenged, a certificate of lawfulness. Do this before you market the property, not during conveyancing.
+Is prior approval the same as planning permission?
No. Prior approval is a neighbour-consultation process for larger single-storey rear extensions under PD. The council can only refuse on the impact on adjoining amenity, not on design generally.