Lighting consultancy

Site planning for daylight and sunlight

Access to daylight and sunlight is a vital part of a healthy environment. Sensitive design should provide sufficient daylight and sunlight to new housing while not obstructing light to existing homes nearby.

The BRE Report Site layout planning for daylight and sunlight: a guide to good practice (BR209) advises on planning developments for good access to daylight and sunlight, and is widely used by local authorities during planning permission to help determine the impacts of new developments.

As authors of the guidelines, we are in a unique position to provide independent and authoritative assessments and reports.

We provide a full daylight and sunlight analysis service, including:

• provision of natural light to new properties
• potential losses to existing properties
• overshadowing
• effects of trees
• potential dazzle from buildings with reflective surfaces
• potential impacts on solar panels
• Rights to Light

This usually involves:
site visit to survey the existing buildings
calculations of daylight and sunlight using our own computer software
report provision or a chapter in an Environmental Statement, suitable for submission as part of a planning permission application.

BRE’s service covers the full range of buildings from domestic extensions to very large developments.

With our expert witness service we can give evidence at planning hearings and public inquiries.

Loss of light to existing buildings

Where a new development can block light to existing homes, daylight assessment for planning is usually based around the vertical sky component (VSC) within and without the new development. This a measure of the amount of diffuse daylight reaching a window.

If the layout of a property is known, the effect on the daylight distribution in the existing rooms can also be analysed.

Overshadowing, or loss of sunlight to existing premises, is analysed using annual probable sunlight hours (APSH). This is a measure of how much sunlight the window can receive with and without the new development.

We advise on how to design a development to reduce or avoid loss of light. For example, we can generate a ‘limiting envelope’, giving the maximum size of the development for loss of light to remain within the BRE guidelines. We can also assess overshading of solar panels on nearby buildings, or on the proposed development itself.

Daylight and sunlight to new developments

We evaluate the daylighting and sunlighting of new developments in line with the latest guidelines in BS EN 17037 ‘Daylight in buildings’ and the BRE Report “Site layout planning for daylight and sunlight: a guide to good practice”. Typical examples range from basement flats and windows in light wells, to high rise urban developments or conversions of commercial properties. For common residential developments, we assess daylighting by calculating room areas achieving a certain daylight factor target), a measure of the amount of daylight in the proposed room. However, we can also carry out more complex calculations using climate based daylight modelling both for residential developments and for special applications like education buildings and museums, or to assess the performance of solar shading devices.

Where not enough daylight is provided, we can advise on changes to the design (providing extra windows, roof lights or light pipes, or changing room layout) to meet the guidelines.

If new housing is planned next to existing trees, we can use our specialist software to show whether enough daylight and sunlight is provided with the trees in place.