Use the council's own adopted-guidance list to establish which document is current. [1] [2]
Find the guide for the right authority
Start with the council area in which the property is located, not its postal description. Look for householder guidance, a residential design guide or an extensions and alterations Supplementary Planning Document, usually shortened to SPD.
For example, Brent lists its Residential Extensions & Alterations SPD as adopted on 16 January 2025. Redbridge's SPD page lists its Housing Design Guide SPD. The titles and dates differ; do not assume an online copy from another borough describes the rules for your property. [1] [3]
Keep the council's publication page as well as the downloaded guide. This helps distinguish an adopted document from a consultation draft or an older version circulating online.
Read the section for the actual proposal
Identify whether the proposal is rear, side, first-floor, two-storey or a combined addition. Then check the guide's wording and diagrams for:
- the scale and relationship to the original house;
- projection, boundary treatment and roof form;
- neighbouring windows and the effect on living conditions;
- materials, street character and any heritage considerations.
Brent's SPD illustrates why this matters: its 45-degree assessment is part of a particular local approach to extensions. The reference point and type of proposal should not be assumed to be the same elsewhere. [4]
Keep local guidance and permitted development separate
An SPD helps explain local planning policy. It cannot enlarge the national permitted development allowance. Equally, a proposal requiring planning permission is not automatically unacceptable merely because it exceeds a permitted development dimension. Compare the preferred design with the applicable local assessment, and identify any departures that need explanation. [1] [2]
Check the property's constraints and previous decisions as well. A generic guide does not establish whether an Article 4 direction or an earlier planning condition has removed rights at the address. [2]
London and Epping Forest use different plan frameworks
In London, borough plans sit within the London Plan framework. The current London Plan was adopted in March 2021. Formal consultation on its proposed replacement runs from 16 July to 15 October 2026; the draft is not an adopted replacement. [5]
For Epping Forest District, use the district's own development plan and local guidance. Its Local Plan was adopted on 6 March 2023. Do not transfer a London borough's extension dimensions or London-wide policy requirements to a district property without an applicable local basis. [6]
The national framework was republished on 17 August 2026. Older design documents may contain historical references; use the current NPPF rather than copying superseded national paragraph numbers into a new application. [7]
Ask the designer to provide a short policy checklist identifying the current documents, the relevant local tests and the evidence the drawings will show.