Supplementary Planning Documents and Design Guides for London Boroughs

A Supplementary Planning Document (SPD) is a document produced by a local planning authority that provides more detailed guidance to supplement the policies in its Local Plan (also called the Local Development Plan or Development Plan Document). SPDs are not primary planning policy — they cannot override or contradict the Local Plan policies to which they relate — but they are material considerations in planning decisions. This means that when a planning officer or planning committee is determining an application, the SPD guidance is a relevant consideration that should be given appropriate weight. SPDs are produced through a public consultation process (though less formal than the examination-in-public required for a Local Plan) and are formally adopted by the local planning authority. They are available on the planning authority's website and on the Planning Portal. Common types of SPD relevant to London householders: Residential Design Guide or Householder Extensions Guide — borough-wide guidance on design standards for extensions, alterations, and householder development; Conservation Area Appraisals and Management Plans — character assessments and design guidance for individual conservation areas; Tall Buildings and Views SPDs — guidance on building heights in areas affected by protected views or landmark sites (particularly relevant in inner London); Biodiversity Net Gain SPDs — guidance on how new development should deliver biodiversity improvements; Parking and Transport SPDs — guidance on car parking provision, cycle parking, and transport assessments; Flood Risk and Drainage SPDs — guidance on development in flood zones and sustainable drainage requirements.

Most London boroughs have a residential design guide or householder extensions SPD that addresses the following: Extension proportions and depth: some boroughs specify maximum recommended depths for single-storey and double-storey rear extensions by house type (terrace, semi-detached, detached). These are guidance, not absolute rules, but departures from them require design justification. The 45-degree line and daylight: most London borough design guides include a version of the 45-degree rule (extensions should not cut across the 45-degree line drawn from the centre of the nearest habitable room window of the adjoining property) as a guide to acceptable daylight impact. Roof forms: design guides typically express a preference for extensions with roof forms that respond to the host dwelling — pitched roofs on pitched-roof houses, flat roofs on flat-roof properties. Some boroughs resist flat-roofed extensions in areas of traditional pitched-roof residential character, while others consider contemporary flat roofs acceptable at the rear. Materials: guidance on the use of materials that are sympathetic to the character of the area — particularly relevant in conservation areas and Article 4 Direction areas. Some boroughs specify that brick and mortar should match the host dwelling; others permit contrasting contemporary materials at the rear where not visible from public views. Window positioning and privacy: guidance on the positioning of windows in side extensions to avoid overlooking of neighbouring properties — typically requiring obscure glazing at first floor level in side windows within 1m of the boundary, or no windows at first floor level within a specified distance of the boundary.

A conservation area character appraisal is the most important planning policy document for homeowners in a designated conservation area. Every conservation area is required to have an appraisal (though some older ones are out of date and are subject to periodic review). The appraisal typically covers: The history and development of the area and why it was designated; the built character — materials, roof forms, window types, boundary treatments, and typical building heights and proportions that define the area's character; the contribution of open space, trees, and landscape to the character; positive buildings and unlisted buildings that make a positive contribution; negative features — aspects that detract from character and opportunities for enhancement; guidance on what development is acceptable and what is not within the conservation area. When an application for an extension in a conservation area is assessed, the conservation officer (a specialist within the planning team) will assess it against the conservation area appraisal. Materials that match the historic character of the area, proportions that respect the scale and rhythm of the streetscape, and details (window reveals, rainwater goods, brickwork bond) that respond to local character are all more likely to receive a positive recommendation from the conservation officer. The conservation area appraisal is typically available on the borough's planning portal and may be presented as a PDF document with maps identifying the character areas, positive buildings, and unlisted buildings that contribute to character.

The most efficient way to identify all SPDs relevant to a specific property in London is: Search the local planning authority's planning portal (almost all London boroughs have online planning portals — search "London Borough of [X] planning" to find the right one). Navigate to the "Planning Policy" or "Local Plan" section and look for "Supplementary Planning Documents" or "Design Guides." Download and read the Residential Design Guide or Householder Extensions SPD (this is the most universally relevant document for homeowners). If the property is in a conservation area (you can check this on the planning portal map or on the Heritage Gateway — historicengland.org.uk/listing/the-national-heritage-list-for-england/), download the specific Conservation Area Character Appraisal and Management Plan for that conservation area. If the property is near a listed building or scheduled monument, check whether there are any area-specific SPDs or heritage setting guidance documents that apply. Search the planning history of the property on the planning portal — previous applications and their decision notices will indicate what SPD guidance was cited by planning officers and whether any material departures from SPD guidance were accepted or refused. If in doubt, a pre-application enquiry with the planning authority (see the Pre-Application Planning Advice guide) is the most reliable way to understand what design standards apply to your specific project.