Daylight and Sunlight

Access to natural light is a vital part of a healthy environment. Sensitive design should both provide sufficient daylight and sunlight to new housing and avoid obstruction and overshadowing of existing homes nearby.

The BRE Report, ‘Site layout planning for daylight and sunlight: a guide to good practice’ (BR209), gives advice on planning developments to make good use of daylight and sunlight, and is widely used by local authorities to help determine the impact of new development.

BRE can provide a full service to analyse daylight and sunlight, including provision to new properties, potential losses to existing ones, Rights to Light, the effects of trees and potential dazzle from buildings with reflective surfaces. This usually involves a site visit to survey the existing buildings; calculations of daylight and sunlight using our own computer software; and providing a report or a chapter in an Environmental Statement, suitable for submission as part of a planning application. We can give evidence at planning hearings and public inquiries. BRE’s service covers a wide range of buildings from domestic extensions to very large developments. Our expertise in electric lighting means we can also assess light pollution from proposed developments and infrastructure.

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) with 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 can give advice 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.

Rights to light

Even if a development receives planning permission, neighbours can still take legal action to protect their Rights to Light (ancient lights). If a court decides that a new development can reduce light in an existing building to insufficient levels, it can grant damages or an injunction to prevent building. BRE’s experts can advise at all stages of the Rights to Light process, including initial guidance, calculation and valuation of the loss of light, negotiations and expert witness services.

Daylight and sunlight to new developments

BRE can carry out evaluation of daylighting and sunlighting of new developments. Typical examples range from basement flats and windows in light wells, to high rise urban developments or conversions of commercial properties. Daylighting is usually assessed by calculating the average daylight factor (ADF), a measure of the amount of daylight in the proposed room. We can also carry out more complex calculations using climate based daylight modelling 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.

Sunshine in gardens and open spaces

We can carry out studies to show whether buildings shade existing or proposed open spaces. Here the BRE guidelines recommend that at least half of the garden or open space can receive at least two hours sunlight on March 21. For larger developments we can provide shadow plots showing the areas in shade at different times of day and year (transient overshadowing). We can also undertake specialist calculations of natural light for plant growth, for example grass in stadiums or plants in nature reserves or internal atriums.

Solar dazzle

BRE can carry out studies to show whether glazing, cladding or solar panels can reflect the sun and cause unwanted glare or dazzle. This can include measurement of the reflective properties of proposed materials in our laboratory or in the field, and specialist calculations of disability glare from reflections to motorists, train drivers or aircraft pilots.

Review service

As well as carrying out daylight and sunlight analysis, we can provide third party reviews and appraisal of daylight and sunlight reports to support local authorities or residents’ groups. We also provide training on planning for daylight and sunlight for councils or other groups.

Daylight research and testing

We have an ongoing programme of research into daylight and sunlight in the built environment. Using our laboratory test facilities, we can measure daylight transmission through light pipes and the light transmission and reflection qualities of different materials.