If you are planning a home extension, a new dwelling, or a larger development in Borehamwood, Elstree, Potters Bar, Radlett, Bushey or Shenley, getting to grips with the daylight requirements in Hertsmere early will save time and reduce planning risk. Daylight, sunlight and overshadowing are routine considerations for the council when it assesses the impact of a scheme on neighbouring homes and on the quality of the accommodation being created. This guide sets out how the local planning authority approaches the topic and what evidence you may need.
Hertsmere Borough Council is the local planning authority (LPA) for the borough. While Hertfordshire County Council is the upper-tier authority, planning applications are decided by the borough council and assessed against its development plan, so it is the borough's policies and guidance that govern daylight matters.
Daylight requirements in Hertsmere: the adopted Local Plan
The development plan is the Hertsmere Local Plan 2012-2027, which is made up of several documents adopted following independent examination. The two most relevant here are:
- the Core Strategy, adopted in January 2013, which sets the strategic framework, including the council's commitment to securing high quality design; and
- the Site Allocations and Development Management Policies Plan (SADM), adopted on 23 November 2016, which contains the detailed development management policies used day to day.
The key policy for daylight and sunlight is Policy SADM30 (Design Principles). To achieve a high quality design, the policy requires that development must “have limited impact on the amenity of occupiers of the site, its neighbours, and its surroundings in terms of outlook, privacy, light, nuisance and pollutionâ€. The explicit reference to light is what brings daylight, sunlight and overshadowing squarely into the assessment. SADM30 also requires development to respect the scale, mass, bulk and height of the surrounding area, and it states that all development should be consistent with Hertsmere's Planning and Design Guide SPD.
For residential schemes, Policy SADM3 (Residential Developments) is also relevant, ensuring new housing provides an appropriate standard of accommodation, which includes adequate internal daylight and usable outdoor amenity space.
Local daylight and sunlight guidance in Hertsmere
Unlike some authorities, Hertsmere does provide dedicated written guidance on the subject. The council's Planning and Design Guide (Supplementary Planning Document) contains specific sections on daylight and sunlight, privacy and outlook, internal space standards, and garden and external amenity space standards. The guide explains that BRE assessments can calculate the amount of daylight and sunlight reaching a property at different times of day and year, and can model the shadow an extension casts, in order to judge the impact on neighbouring windows. It also gives practical advice, for example that roofs should not be so high that they block sunlight and daylight to a neighbour's house and garden, and that first-floor extensions will usually be expected to have pitched or hipped roofs.
The technical benchmark behind this guidance is the national standard: BRE BR 209 (2022), Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice, read together with BS EN 17037 on daylight in buildings. These are applied through the Local Plan and the National Planning Policy Framework (NPPF), which expects a high standard of amenity for existing and future occupants.
A BRE-based assessment normally examines:
- Vertical Sky Component (VSC) and daylight distribution at affected windows;
- Annual Probable Sunlight Hours (APSH) for rooms with a significant southerly aspect;
- Overshadowing of gardens and amenity space, commonly tested for sunlight on the ground on 21 March.
What makes Hertsmere distinctive
Hertsmere has a particular geography that shapes its daylight considerations. A very large proportion of the borough is designated Green Belt, which concentrates development pressure on the existing built-up areas of Borehamwood, Potters Bar, Bushey and Radlett. In these settlements, intensification, backland development and flatted schemes are common, and these are exactly the situations in which neighbour daylight and overshadowing become decisive.
Borehamwood and Elstree are also internationally known for their film and television studios, and the regeneration of the Elstree Way Corridor is guided by its own Area Action Plan, which brings forward higher-density mixed-use development where careful daylight and sunlight design is especially important. Hertsmere additionally protects areas of distinctive character, including the Bushey Heath former Ministry of Defence housing area (Policy SADM31), where the spacing, sky gaps and open setting between buildings are valued, factors that interact directly with massing and overshadowing.
How Fortress Associates can help
Fortress Associates prepares clear, robust daylight and sunlight assessments to BRE BR 209 (2022), BS EN 17037 and the NPPF, interpreted through the Hertsmere Local Plan and the Planning and Design Guide. Whether you are extending a home in Potters Bar or bringing forward flats in Borehamwood, our daylight and sunlight report service can test your scheme against the relevant benchmarks, flag neighbour impacts early, and support your application. We work UK-wide, with a typical turnaround of four to five working days and no advance payment required. Explore our services page for the full picture, or contact us to talk through your project. You may also find our guides on daylight requirements in Watford and daylight requirements in Welwyn Hatfield useful.
Sources & further reading
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