Planning Drawings for a London Extension: What You Need and Who Prepares Them
A planning application for a house extension requires a specific set of drawings and supporting documents. Submitting an incomplete or poorly prepared application is one of the most common causes of unnecessary delays. This guide sets out exactly what is needed for a householder planning application in London and who prepares each element.
Who Prepares Planning Drawings?
Planning drawings for residential extensions in London are typically prepared by:
- Architects (RIBA registered): The most comprehensive service. Can take the project from concept through planning, building regulations, and technical design. Best for complex or high-value projects.
- Architectural technologists (CIAT registered): Strong technical expertise. Often more cost-effective than a full architectural service for straightforward extensions.
- Architectural designers or planning consultants: Experienced practitioners who may not hold chartered status but have a track record in residential planning work. Variable quality — check previous applications they have submitted and their success rate.
- Design and build contractors: Some contractors, including RCB, offer pre-construction design coordination as part of a design-and-build package, either directly or via partner designers.
The Standard Documents Required
1. Application Form (1APP)
The standard householder planning application form (1APP), completed online via the Planning Portal. Covers property address, description of development, applicant and agent details, and declarations.
2. Location Plan (Scale 1:1250)
A plan showing the application site in relation to the surrounding area — typically sourced from Ordnance Survey mapping. The application site boundary is shown in red; any additional land in the applicant's ownership is shown in blue.
Key requirement: The red line must include all land required to carry out the development (including areas of scaffolding, temporary access, etc.).
Councils sell these maps via the Planning Portal, or your designer will obtain them. Cost: approximately £20–£50.
3. Site Plan (Scale 1:500 or 1:200)
A plan showing the application site in detail, including:
- The footprint of the existing building
- The footprint of the proposed extension (in solid or hatched)
- Key dimensions
- Relationship to boundaries, neighbouring buildings, and access points
- North point
4. Existing Floor Plans (Scale 1:100 or 1:50)
Floor plans showing the existing layout of the building, room by room, at each level affected by the application.
Common mistake: Submitting floor plans that do not match what is actually on site. The planning officer will compare submitted drawings with the real building — discrepancies cause delays and can invalidate an approval.
5. Proposed Floor Plans (Scale 1:100 or 1:50)
Plans showing the proposed layout after the extension is built, at each level affected. Should clearly show:
- New rooms and their use
- Connection between extension and existing building
- New openings, windows, and doors
- Removal of any walls
6. Existing Elevations (Scale 1:100 or 1:50)
Drawings showing the external faces of the existing building — at minimum the rear elevation and any side elevations where the extension will be visible.
7. Proposed Elevations (Scale 1:100 or 1:50)
External elevation drawings of the proposed development, showing:
- The new extension in context of the existing building
- Window and door positions
- Roof form, pitch, and ridge height
- Materials notation (brick type, render colour, roof covering, window material)
- Key dimensions: maximum height, eaves height, extension depth
8. Existing and Proposed Sections (where required)
Section drawings showing a cut through the building, illustrating internal floor-to-ceiling heights and the relationship between the extension and the existing structure. Required where height relationships or basement levels are relevant.
9. Planning Statement or Design and Access Statement
Design and Access Statement (DAS): Required for applications affecting a Conservation Area or a listed building. Also advisable for any application that may face scrutiny on design grounds. Sets out the design rationale, how the proposal responds to its context, and how it complies with local policy.
Planning Statement: More detailed than a DAS; typically used for larger or more complex applications where policy compliance needs explicit demonstration.
For a straightforward householder application in a non-designated area, a brief covering letter or description of the development may suffice — check the specific requirements of your borough.
10. Heritage Statement
Required where the property or setting is listed or within a Conservation Area, and where the development could affect the significance of the heritage asset. Should demonstrate that the development preserves or enhances character.
11. Arboricultural Survey
Required where there are trees on the application site or adjacent to it that could be affected by the development. A BS 5837:2012 tree survey identifies the trees, assesses their quality and root protection areas, and specifies protection measures during construction.
12. Ecological Survey
Required where there is a realistic possibility of protected species (bats, breeding birds, great crested newts) being present. Councils increasingly request these for rear extensions affecting garden areas.
The Planning Fee
From April 2024, the planning fee for a householder application in England is £258. This is non-refundable.
After Submission
Once validated by the council, you will receive a planning reference number and a target decision date (8 weeks from the validation date). You can track the application online on the council's planning portal.
RCB Design & Build
RCB coordinates planning applications for extensions as part of our design-and-build service, working with experienced architectural designers who understand London borough requirements. We prepare and submit all required documents and manage the process through to decision. Contact us to discuss your extension.