Understanding daylight requirements in Cardiff is essential for anyone proposing residential development in the Welsh capital. As a dense, historic city with extensive Victorian terraces, a fast-growing city centre and tall-building clusters around Cardiff Bay, Cardiff is one of the more daylight-sensitive planning environments in Wales. The City of Cardiff Council assesses light through a combination of its adopted development plan, detailed supplementary guidance and recognised best-practice methodology. This article sets out how that framework operates and what applicants should expect.
The planning framework in Cardiff
Planning decisions in Cardiff are made against the adopted Cardiff Local Development Plan 2006–2026, which the Council adopted on 28 January 2016. The LDP remains the statutory development plan for the city, although the Council is preparing a Replacement Local Development Plan (covering the period to 2036) which is progressing through its plan-making stages and is not yet adopted. Until the replacement plan is adopted, the 2006–2026 LDP carries full weight.
Two LDP policies are central to amenity and light:
- Policy KP5 – Good Quality and Sustainable Design. This key policy requires development to be of high quality and to protect the amenity of both new and existing occupiers, addressing privacy, outlook and overshadowing among many other design considerations.
- Policy EN13 – Air, Noise, Light Pollution and Land Contamination. EN13 works alongside KP5 to ensure development does not cause unacceptable harm to the amenity of neighbouring occupiers and the wider area.
These local policies sit beneath the wider Welsh planning framework. Planning Policy Wales (Edition 12, 2024) sets the national policy on placemaking and good design, supported by Future Wales: the National Plan 2040 and the design-focused Technical Advice Note (TAN) 12: Design. Daylight and sunlight are treated as a core component of amenity and good placemaking under this framework. Applicants should note that the English National Planning Policy Framework does not apply in Wales.
How Cardiff assesses daylight and sunlight
The most detailed and specific guidance comes from Cardiff's Infill Sites Supplementary Planning Guidance (November 2017), which sets out exactly how the Council expects daylight and sunlight to be evaluated. This SPG is particularly relevant given the volume of small backland and infill plots within Cardiff's terraced streets.
Cardiff's guidance states plainly that the assessment of sunlight and daylight is based on the BRE publication Site Planning for Daylight and Sunlight – a guide to good practice. The Council uses two well-known geometric tests as triggers:
The 25-degree rule
The first test applies to windows facing other buildings or structures. A building obstructs reasonable light to a relevant window if it breaks a line projecting up from the centre of the window at 25 degrees from the horizontal. Where this line is breached, applicants are required to prove the window is not adversely affected by quantifying daylight using the Skylight Indicator or Waldram diagram methods set out in the BRE publication. The Cardiff SPG specifies that the measure of daylight reaching a window should not fall below 27%.
The 45-degree rule
The second test applies to extensions projecting from an existing building line. An extension obstructs reasonable light if it breaks a line projecting 45 degrees from the centre of an affected window, assessed both horizontally (in plan) and vertically (in elevation). Pitched-roof extensions are assessed from the centre of the pitch. The guidance specifically warns against the “tunnelling effect” where a window is hemmed in by extensions from two directions.
The SPG is clear that these standards apply equally to impacts on both new and existing buildings, and that schemes failing to meet them “will be resisted without further justification or other reasonable measures being in place to provide adequate light.” The tests are applied as a trigger for further justification rather than as an absolute pass/fail, with some flexibility recognised where light can reach living spaces by other means.
Affected rooms and single-aspect units
Cardiff's assessment focuses on habitable rooms used as main daytime living spaces. Small kitchens, bathrooms, toilets, circulation spaces and storerooms are excluded, and bedrooms are only included where they form part of daytime living space. There is a clear presumption against single-aspect units unless the design is shown to allow adequate daylight and ventilation to all habitable rooms, with dual-aspect dwellings strongly preferred.
Privacy, overshadowing and separation distances
While distinct from daylight, Cardiff's amenity standards interact closely with light. The Infill Sites SPG sets a normal minimum of 21 metres between principal habitable-room windows and a minimum overlooking distance of 10.5 metres from a habitable-room window to a neighbour's garden. To safeguard existing residents, proposals must not cause unacceptable harm through overbearing impact, overshadowing or overlooking. On sunlight, the guidance notes that windows facing within 90 degrees of due south will gain direct sun, and that living rooms should be designed to receive a reasonable amount of it.
Cardiff-specific considerations
Several local factors make daylight assessment particularly important in Cardiff:
- Victorian terraces and backland plots. Large parts of Cathays, Roath, Grangetown and Canton consist of tightly packed terraced housing where rear extensions and backland infill quickly engage the 45-degree and 25-degree tests. Cardiff's SPG treats tandem development behind existing homes as generally unacceptable.
- Tall buildings and Cardiff Bay. Cardiff has separate Tall Buildings supplementary guidance focused on the city centre and bay areas, where height and massing make overshadowing and daylight impacts on surrounding development a key consideration.
- Larger residential schemes. Proposals of 10 or more dwellings are expected to follow the Cardiff Residential Design Guide and submit a Design and Access Statement, within which daylight and sunlight evidence is routinely scrutinised.
For developers and homeowners alike, the practical message is consistent: prepare credible BRE-based daylight and sunlight evidence early, and be ready to demonstrate compliance with both the geometric tests and the underlying numerical measures.
How Fortress Associates can help
Fortress Associates prepares our daylight and sunlight report service to BRE BR 209 (2022) and BS EN 17037, presenting the evidence Cardiff Council expects to see, including 25-degree and 45-degree assessments and Skylight Indicator analysis where required. We also produce Building Regulations drawings. We work nationwide with a 4–5 working day turnaround and no advance payment. Contact us to discuss your Cardiff scheme.
Sources & further reading
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