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A guide to Rights of Light

A "right to light" is a legal entitlement that gives an established property owner the right to receive light through existing apertures, such as windows and doors, in buildings on their land. A right to light is protected under common law (The Ancient Lights Law), and is acquired in England and Wales by the Prescription Act 1832.

An owner of a building with windows that have received natural daylight for 20 years or more may be entitled to restrict any construction or other obstruction that would deprive him or her of “sufficient light according to the ordinary notions of mankind” (1904). Alternatively, they may seek compensation in lieu of such rights.

Since the 1920s, experts have used a method proposed by Percy Waldram to assist them with the calculation of “visible sky factors” and the principle that ordinary people require one foot-candle of illuminance (approximately ten lux) for reading and other work involving visual discrimination. The current method for assessing Rights to Light is by using a 3D computer model and specialist software to undertake a detailed analysis of current and proposed conditions. Clearly, the more accurate and complete the 3D model, the better and more precise the assessment. For this reason the RICS Professional Guidance for Rights of Light (2nd Edition) endorses the use of a full measured survey to establish the most accurate 3D models. It goes further to recommend that this is best achieved using High Definition terrestrial 3D laser scanners.

To emphasise the importance of an accurate measured Rights of Light survey the latest RICS Professional Guidance for Rights of Light (2nd Edition) now provides a link to RICS Guidance in Measured Surveys of Land, Buildings and Utilities 3rd Edition 2014 which sets out the accuracy requirements for a measured Rights of Light survey.

MSA is the pre-eminent leader in measured Rights of Light surveys having specialised in this type of work for over 28 years. We were one of the first to adopt 3D laser scanners for Rights of Light site measurement and have an unsurpassed understanding of the software, technical assessment process and its implications. Our knowledge and experience has resulted in our involvement on most of the significant development schemes in London.

All of our Rights of Light surveys are based on Ordnance Survey (OS) grid and datum and we ensure maximum coverage of the assessment buildings by scanning from site roofs and elevated scanning platforms. Our site measurements are supplement by high resolution photography which, if necessary, can be enhanced using high level masts or drones.  Our site work is supplemented by research, and we work closely with our partner Vertex Modelling by using their data obtained from aerial photogrammetry for those areas that are not visible from the constraints of the site, site roof or surrounding public areas.

But successful surveying is not just all about the data capture and the 3D modelling. An extensive knowledge of the Rights of Light software and technical process is equally crucial. Providing the Rights of Light consultant with additional detail on wall thicknesses, internal room layouts and internal floor or ceiling heights gleaned from the scan data is invaluable. Furthermore, information regarding room usage and identifying dual aspect layouts together with site observations and relevant data enhances and streamlines the assessment process.

To ensure that London maintains its outstanding position in the global economy  it is crucial that the laws by which rights to light are acquired and enforced provide an appropriate balance between the important interests of property owners and the need to facilitate the appropriate levels of redevelopment and expansion. 

MSA have worked alongside all of the London Rights of Light consultants in partuicular we have a longstanding relationship with Rights of Light specialists GIA which spans over 28 years. For more information on Rights to Light advice please contact GIA on 0207 202 1400.