Understanding the daylight requirements in Na h-Eileanan Siar matters to anyone planning a house extension, a new dwelling or a small development in Stornoway or across the islands of Lewis, Harris, the Uists, Benbecula and Barra. Comhairle nan Eilean Siar, the Western Isles Council, is the planning authority for the area, and it assesses how a proposal affects the amenity, light and outlook of neighbouring homes against the policies in its adopted development plan and supporting design guidance. This article explains how those requirements work in practice for an island authority, and how a professional daylight and sunlight report can support your application.
The planning framework in Na h-Eileanan Siar
Planning decisions in the Western Isles are made against the statutory development plan, which has two parts. The first is National Planning Framework 4 (NPF4), adopted by the Scottish Government in February 2023, which now forms part of the statutory development plan across the whole of Scotland. The second is the council's own Outer Hebrides Local Development Plan 2018 (LDP), which was adopted on 19 November 2018 and superseded the previous plan of 2012. A replacement plan has been progressing through its statutory stages, but until it is adopted the 2018 plan remains the local statutory basis for decisions.
The most relevant policy strands for daylight and amenity are:
- NPF4 Policy 14 (Design, quality and place) and Policy 16 (Quality homes), which require development to create well-designed, sustainable places and to provide good-quality residential amenity, including adequate daylight and sunlight.
- LDP Policy PD1 (Placemaking and Design), the principal design test for new buildings.
- LDP Policy PD6 (Compatibility of Neighbouring Uses) and Policy PD3 (Housing), which protect the amenity of neighbours.
An honest word about island guidance
It is worth being straightforward about this. Na h-Eileanan Siar is a small, remote island authority, and its development plan does not contain a bespoke numerical daylight or sunlight standard, nor a dedicated technical daylighting supplementary guidance document of the kind some larger mainland cities publish. The plan does not set out a 25 degree rule or a vertical sky component target in its text. Instead, daylight is dealt with through the broader, amenity-based design policies described below, supported by the Outer Hebrides Design Guide, and assessed case by case. Where a proposal raises a genuine question of loss of light or overshadowing, the council can and does call for evidence, and best-practice methodology is used to provide it.
What the Outer Hebrides Local Development Plan says
Policy PD1 (Placemaking and Design) is the central design policy. It requires that development proposals demonstrate a satisfactory quality of placemaking, siting, scale and design that respects and reflects positive local characteristics and complements or enhances the surrounding built and natural environment, while taking account of the guidance in the Outer Hebrides Design Guide. Among its criteria, PD1 requires that the siting and orientation of development relate to the settlement pattern, landform and the characteristics of the surrounding area, and that amenity space and landscaping are commensurate with the scale and character of the development. Siting, orientation and spacing are precisely the factors that determine whether neighbours retain adequate daylight and sunlight, so PD1 is the policy under which light and overshadowing are most often considered.
Policy PD6 (Compatibility of Neighbouring Uses) reinforces this. It states that all development proposals shall ensure that there is “no unacceptable adverse impact on the amenity of neighbouring uses”, and that mitigation should be included where appropriate. Loss of daylight, sunlight and outlook fall squarely within this protection of neighbouring amenity. For new homes themselves, Policy PD3 (Housing) and the wider design policies expect a good standard of residential amenity.
How daylight is actually assessed in practice
Because the LDP sets the amenity requirement but not the method, the detailed assessment is carried out using nationally recognised best practice. In daylight and sunlight work that means the Building Research Establishment (BRE) guide BR 209, ‘Site Layout Planning for Daylight and Sunlight: A Guide to Good Practice’, in its 2022 third edition, alongside the British Standard BS EN 17037. These provide objective tests that allow an applicant to demonstrate, and a planner to judge, whether a proposal complies with the amenity and design aims of PD1, PD6 and NPF4.
A BRE-based daylight and sunlight assessment typically considers:
- The 25 degree rule of thumb – if an obstruction rises at more than 25 degrees from the horizontal, measured from the centre of a neighbour's lowest window, daylight may be at risk and detailed checks are needed.
- The 45 degree test – used to judge the effect of extensions built at an angle to a neighbour's window, on both plan and elevation.
- Vertical Sky Component and daylight distribution – the BRE's detailed measures of how much skylight reaches a window and how it spreads across a room.
- Annual Probable Sunlight Hours – a check on sunlight to principal living rooms and to garden and amenity spaces.
The northern latitude of the Western Isles makes light a particularly meaningful consideration. The low winter sun angle means that the relationship between buildings, their orientation and the spacing required by PD1 has a real effect on how much sunlight reaches living rooms and gardens, which is exactly what a sunlight study can quantify.
What this means for your project
Whether you are extending a house in Stornoway, building a new home in a township on Lewis or Harris, or developing on the Uists or Barra, the council will want to be satisfied that your proposal does not cause an unacceptable adverse impact on the amenity of neighbours, in line with PD1 and PD6. A daylight and sunlight assessment is most often helpful where:
- An extension or new building would breach the 25 degree line from a neighbour's window;
- A new dwelling sits close to an existing home, particularly on a constrained plot in Stornoway;
- A planning officer or objector raises overshadowing, overlooking or loss of light;
- You want to show that new homes will themselves enjoy good daylight and winter sunlight.
Producing a clear, BRE-based report at the application stage helps an officer reach a positive recommendation and answers neighbour concerns with objective evidence rather than assertion.
How Fortress Associates can help
Fortress Associates provides a professional daylight and sunlight report service prepared to BRE BR 209 (2022) and BS EN 17037, the recognised best-practice methodology used to demonstrate compliance with the amenity and design policies of the Outer Hebrides LDP and NPF4. We assess the 25 and 45 degree tests, run the detailed BRE daylight and sunlight calculations where needed, and check overshadowing and outlook so your application is supported by clear evidence. We work UK-wide, including the islands, with a turnaround of 4 to 5 working days and no advance payment. We also prepare building warrant and Building (Scotland) Regulations drawings. To discuss your project in Stornoway or across the Western Isles, please get in touch.
Sources & further reading
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