Planning Permission for Extensions: When You Need It and How to Get It

**The starting point — permitted development**:

Most single-storey rear extensions to a house (not a flat) in England are permitted development (PD) under Part 1, Class A of Schedule 2 of the GPDO 2015 — meaning they do not require a planning application. The PD allowance for extensions:

• *Standard PD allowance (Class A)*:
• •Terraced and semi-detached: up to 3.0m from the original rear wall (depth measured at the rearmost point of the extension from the nearest existing rear wall of the original dwelling)
• •Detached: up to 4.0m depth
• •Maximum height: 4.0m; eaves ≤ 3.0m if within 2.0m of a boundary
• •Must not be higher than the main house
• •Not visible from a highway at the front of the house
• •Materials similar in appearance to the existing house
• •No veranda, balcony, or raised platform

• *Extended PD allowance (Prior Approval Neighbour Consultation Scheme)*:
• Single-storey rear extensions exceeding 3m (terraced/semi) or 4m (detached) are also PD up to 6m or 8m respectively, provided:
• •A Prior Approval notification (PA5 form) is submitted to the LPA before starting
• •The LPA runs a 21-day neighbour consultation
• •Prior Approval is confirmed in writing before work starts
• •The extension is single-storey only

*Side extensions*: Single-storey side extensions are PD if they do not exceed 50% of the original house width AND are not in a Conservation Area. Two-storey side extensions are NEVER PD.

*When planning permission IS required for extensions*:

• •Two-storey extensions (any type — rear, side, or wrap-around) — always require planning permission
• •Extensions in Conservation Areas (side extensions; front extensions; extensions that are visible from a public road or open space)
• •Extensions that exceed the PD volume/depth limits (including where previous extensions have already used some of the PD allowance — the PD allowance relates to the original dwelling, not the current footprint)
• •Extensions to flats — PD rights do not apply to flats; all extensions require planning permission
• •Extensions to listed buildings — both planning permission AND Listed Building Consent are required
• •Where an Article 4 Direction has removed PD rights
• •Front extensions (any extension forward of the principal elevation or side elevation fronting a highway)
• •Extensions with a balcony or elevated terrace visible from a highway

**The most common mistakes**:

1. *Measuring from the wrong point*: PD depth is measured from the 'original rear wall' of the 'original dwelling' — not from the current rear wall if a previous extension was already built. If a rear extension was built previously, that extension is the new measurement baseline — so the PD depth available may be reduced or eliminated. 2. *Not checking if PD rights have been removed*: Article 4 Directions and conditions on previous planning permissions frequently remove Part 1 PD rights. Always check the planning history on the LPA portal before assuming PD applies. 3. *Conservation Area assumptions*: In a Conservation Area, side extensions are not PD regardless of size. Always check Conservation Area status. 4. *Not obtaining a CLD*: Building a PD extension without a Certificate of Lawful Development (CLD) is technically lawful but leaves no formal record — problematic on sale.

**Types of planning application for extensions**:

*Householder Application (HA)*: The standard application type for most domestic extensions, loft conversions, and other works to a dwelling house. Fee: £258 for a householder application in England (as of 2024 — fees may change; check the Planning Portal for current fees).

*Prior Approval Application (PA5)*: For extended PD extensions (6m/8m single-storey). No application fee. Processed under the Neighbour Consultation Scheme.

*Certificate of Lawful Development (CLD) — Proposed*: Not a planning application but a formal confirmation that proposed works are lawful PD. Fee: £206.

**What a planning application for an extension requires**:

• *Mandatory documents*:
• •*Completed application form*: Submitted online at planning.gov.uk/planning/applications
• •*Location plan*: An OS extract showing the site in relation to surrounding streets, at scale 1:1250 or 1:2500, with the application site outlined in red. Can be purchased from the Planning Portal.
• •*Site plan*: Showing the existing and proposed site boundaries, with the application site shown, at scale 1:200 or 1:500
• •*Existing floor plans*: Current layout of the house, to scale
• •*Proposed floor plans*: Proposed layout including the extension, to scale
• •*Existing and proposed elevations*: All elevations showing the existing house and the proposed extension on the relevant elevations, to scale, with materials labelled
• •*Existing and proposed sections* (if relevant — e.g., for split-level sites)

*Local requirements (LPA-specific)*: Some LPAs require additional documents — a Design and Access Statement (required for extensions in Conservation Areas, or for works to listed buildings); Heritage Statement (works affecting listed buildings or their settings); Arboricultural Report (where trees are affected).

**The decision-making process**:

• •*Application validated*: LPA checks the application is complete and starts the statutory determination period
• •*Statutory period*: 8 weeks for a householder application from the date of validation
• •*Consultation*: The LPA consults neighbours (typically 14–21 days), the Council's design, conservation, or highways teams (where relevant), and may consult Historic England (for listed buildings)
• •*Decision*: Grant (with or without conditions) or refuse
• •*Conditions*: Most planning permissions have conditions (e.g., no development to start until materials have been submitted and approved; development to be completed within 3 years; drainage strategy to be implemented as approved)

**What planning officers assess**:

For a householder extension application, planning officers assess against the Local Plan policies for residential extensions. The key material considerations are:

• •*Impact on the host dwelling*: The extension should be subordinate to the main house in scale and design; should not dominate or unbalance the existing building
• •*Impact on neighbours*: Overlooking (privacy), overshadowing (daylight/sunlight), and overbearing impact on the principal windows of immediately adjacent dwellings
• •*Impact on streetscape and Conservation Area character* (where applicable)
• •*Design quality*: Materials, fenestration pattern, and relationship to the existing dwelling

**Appealing a refusal**:

If the LPA refuses a householder application, you can appeal to the Planning Inspectorate within 12 weeks of the refusal decision. Most householder appeals are decided by the written representations procedure (no hearing required); average appeal determination is 12–18 weeks. The Planning Inspectorate allows approximately 40% of householder appeals. A pre-application discussion with the officer before submitting is the better way to understand the likely outcome — if refusal is signalled, redesign before submitting rather than appealing a refusal.

**London-specific planning context for extensions**:

London LPAs operate within the framework of the National Planning Policy Framework (NPPF), the London Plan (issued by the Mayor of London), and their own Local Plans. For residential extensions, the local plan policies of the specific LPA are most relevant — and they vary considerably between boroughs.

**Key London factors**:

*Conservation Areas*: A very large proportion of London residential streets are within Conservation Areas. In Conservation Areas, design quality, materials, and consistency with the character of the area carry significant weight. Flat-roof extensions on Victorian and Edwardian terraces in Conservation Areas are often refused; pitched or slate-covered roofs, stock brick, and timber windows are viewed more favourably.

*SPDs and residential design guides*: Most London LPAs have Supplementary Planning Documents (SPDs) specifically for residential extensions. These set out detailed guidance on design, materials, scale, and proportions. Reading the relevant SPD before designing an extension significantly improves approval chances.

*Pre-application advice*: Most London LPAs offer a paid pre-application planning advice service where you can meet a planning officer and get their view on a proposal before submitting. Fee: £200–£500 for a householder pre-application. This is money well spent where there is any uncertainty about the policy position — it identifies fundamental issues before design fees are committed.

*Overlooking in dense urban areas*: London gardens are often short and overlooked from multiple directions. The standard test of 21m between facing habitable windows (from the London Plan and most Local Plans) can be difficult to satisfy in dense urban settings. Careful positioning of windows, obscure glazing to side windows, and roof lights (rather than dormer windows with overlooking potential) all help.

*Materials*: 'Materials similar in appearance to the existing house' is often cited as a condition for PD works; for full planning applications, matching stock brick, slate, and original window proportions are almost always required in Conservation Areas and in most sensitive locations. Always specify materials that match or complement the existing house — a flat-roof extension in render on a Victorian brick terrace in a Conservation Area is a near-certain refusal.

**Getting the design right before applying**:

The most common mistake with planning applications is submitting a poorly designed or undersized scheme without professional architectural input, then having to redesign after refusal. A pre-application discussion with the LPA officer, followed by an architect-prepared design that specifically addresses the officer's concerns, significantly increases the chance of first-time approval. Planning fees and preparation costs for a refused application that must then be redesigned and resubmitted are wasted.