An issue that crops up on a regular basis for new development irrespective of size and scale and now with the added test for the Prior Approval conversion of existing office buildings, is ‘light’ – how much is there?; is there too much, enough or too little?; does the development block anyone else’s light?; does the proposal overshadow neighbouring properties and gardens?;  and should non-planning legal issues relating to Rights to Light be tackled in conjunction or not? These are all valid questions that are becoming increasingly important as we are required to design higher density developments, convert existing buildings to residential use and witness an increasing prevalence of taller buildings within our cities. So we thought who better to help us steer you through this complex issue than Dan Tapscott, Partner and Head of Neighbourly Matters at Rapleys (@DanTapscott, @RapleysLLP, ). 

Light is an issue that will be considered by a case officer, so should be assessed by the design team during the design development of a proposal. As with other amenity considerations, issues surrounding light can be fundamental to securing planning consent. You might not have thought about it, or have dismissed it as a regulatory matter. But it’s much more than that. If you are unable to demonstrate that your proposal will not have an adverse impact on light levels for future occupants or neighbours then your proposals may be unacceptable in principle. And then, if Rights to Light issues have not been considered, a planning approval may not be implementable. So, before the design of your development advances we recommend giving  some thought to the following:

Are there different types of light? 

When assessing the impact on light on and from a proposal, consideration will need to be given to daylight and sunlight.

‘Daylight’ is defined as being the volume of natural light that enters a building to provide satisfactory illumination of internal accommodation between sunrise and sunset. It has nothing to do with the position of the sun or orientation of buildings; it is diffuse light from the sun across the sky – the blue sky received by the apertures (most commonly windows, but also doors and rooflights) and into the rooms.

‘Sunlight’ refers to direct sunshine or the sun’s rays.  It is useful to remember that the sun rises in the east and sets in the west; the sun reaches its maximum height around noon and will generally be due south at this time; and the sun is higher in the sky in summer months as opposed to winter months. Here we consider the time this reaches the apertures as well as to external amenity spaces (gardens, parks, playgrounds etc).

Is the impact on daylight and sunlight regulated?

Yes, is the quick and easy answer to this question from a planning perspective. From a Rights to Light point of view it’s not. It is pretty much standard practice for a Local Plan to contain policies that require proposals to minimise or mitigate their impact on daylight and sunlight levels of neighbouring properties and to receive good levels themselves. Consequently, a case officer will assess these considerations based upon the information submitted against planning policy requirements.  

In the majority of cases Local Plan policies relate to the guidance published by the BRE (Building Research Establishment).  BRE Report 209: Site layout planning for daylight and sunlight: a guide to good practice (2011 2nd edition), contains nationally applicable best practice guidelines on the levels of daylight and sunlight that existing and new development should follow. Although not mandatory and intended to be used flexibly to reflect relevant situations, it does provide the standard advice on daylight and sunlight assessments.  This document provides a great starting point to determine what, when and how to assess the impact of your proposal and conversely, making best use out of the development site.

Rights to Light are a civil matter relating to easements. If neighbouring properties enjoy Rights to Light and they will be infringed by the increased massing of a proposal to an unreasonable degree, then the implications can be significant on a proposed development. At their worst, injunctions can be awarded (up to 6 years after the injury commences) to remove the offending part of the development, even if it is occupied. Alternatively, large sums of compensation can take a long time to negotiate at a critical point in the development programme. So get this issue sorted out at the earliest opportunity. 

What are the wider planning considerations in assessing appropriate levels of daylight and sunlight?

It’s a no-brainer, all developments should ensure acceptable living standards both for future occupants and neighbours – you and the LPA wouldn’t expect anything less. LPAs expect new developments to follow the BRE guide and provide suitable mitigation where levels fall below target values. 

Importantly, from April 2021 Prior Approval Notification applications submitted under Class O (soon to be Class MA) of Part 3 of Schedule 2 of The Town and Country Planning (General Permitted Development) (England) Order (as Amended) 2015 for the change of use of an existing office building (Class E(g) – formerly B1a) to residential use (C3) are expected to ensure that all habitable rooms receive adequate natural light. This is good news as common sense has finally prevailed as nobody wants to live in a gloomy, dingy box of a room, even if certain developers want to build them!   

What this means in practice, in relation to assessing appropriate levels of daylight and sunlight, will depend to some extent on the context for the development as well as its detailed design. For example in areas of high-density historic buildings, or city centre locations where tall modern buildings predominate, lower daylight and daylight and sunlight levels at some windows may be unavoidable if new developments are to be in keeping with the general form of their surroundings. In such situations good design (such as giving careful consideration to a building’s massing and layout of habitable rooms) will be necessary to help make the best use of the site and maintain acceptable living standards.


It is incumbent on the design team to ensure that adequate natural light levels, in terms of both daylight and sunlight, can be achieved within new development and unacceptable impacts on light for nearby properties are minimised, or preferably avoided.  A proposal must assess the loss of light to existing buildings generated by new development as well as the levels of light new development provides itself. 

Accuracy in assessments is increasingly coming under scrutiny. It is essential that the site, relevant neighbouring properties and surrounding context have been modelled correctly. Analysis software is fairly uniform throughout the industry but it is essential that all the necessary testing has been carried out in order to fulfill the BRE requirements to enable the consultant to give an honest conclusion in their report and make the case officers job to review the report with confidence, an easy one.

Initial Understanding 

A preliminary review of the outline proposals will highlight initial concerns in terms of their design, layout, orientation and impact upon the neighbouring properties. Importantly, this subject involves ‘habitable’ rooms only such as kitchens and living rooms. Bedrooms are included, but the BRE acknowledges these are ‘less important’. Other rooms with a reasonable expectation of good levels of natural light such as classrooms and some workshops will also need considering. Non-habitable rooms such as hallways, stairwells, cupboards and bathrooms ‘need not be assessed’ in accordance with the BRE Report. It is the convention that rooms where use of artificial light is the norm, such as offices, do not warrant consideration. Although with a trend toward homeworking, the importance of maintaining good levels of daylight within spare bedrooms has never been more important to occupiers.

If a Daylight & Sunlight practitioner is involved early enough most will be able to offer reverse engineering of the process and undertake an envelope study which will guide the architect, giving them a framework to work within and avoid impacts to the neighbours.

The BRE Report contains a preliminary test for considering the impact on daylight using simple rules of thumb and then gives examples of best practice elsewhere. Should the preliminary test fail then a more detailed study using 3D computer based models is warranted. These can also be used for Rights to Light analysis.

A good Daylight & Sunlight practitioner should be able to determine whether a scheme warrants an analysis very quickly and often for nil or at minimal cost. 

Analysis for neighbouring properties

There are a number of ways of assessing the impact of a proposal on neighbouring properties. 

The Vertical Sky Component (VSC) is a measure of the amount of light falling on a window; it is quantified as a ratio of the direct sky illuminance falling on the surface at a specific reference point against the horizontal illuminance under an unobstructed sky. The maximum possible ratio is just under 40% for a completely unobstructed vertical wall. The VSC values attained by windows of a building will not vary with the compass orientation of that building; therefore orientation does not give an appreciation of the interior daylighting. The target value recommended is 27% but this is not to be strictly applied. This is because if the VSC for a window is less than 27% and is less than 0.8 times its former value, the BRE numerical guidelines will not be satisfied. However, if the VSC is less than 27%, but more than 0.8 times its former value then daylight levels might still be adequate to the neighbouring property. It’s useful to consider the Reduction Factor of 0.8, as a percentage equal to 80%, or put another way, a 20% reduction is recommended as the guideline figure within the BRE Report.

With regard to assessing Sunlight, the BRE Report gives recommendations for the assessment of the effect on sunlight enjoyed by individual windows. When considering sunlight, in the northern hemisphere, it is only those windows that face within 90 degrees of due south that will enjoy significant amounts of Sunlight. The BRE Report limits the extent of assessments required to only these windows. Sunlight Amenity is measured in terms of Annual Probable Sunlight Hours (APSH). The assessment analyses a point in each window which receives at least a quarter of APSH. This includes at least 5% of APSH during the winter months, between 21st September and 21st March. Again, a Reduction Factor of 0.8 is also applied to the results.

The Daylight Distribution (DD) is otherwise known as the ‘no sky-line’ (NSL) method and takes the VSC analysis a step further in looking at where in the room Daylight is received at the working plane (roughly desk or kitchen worktop height). After a development is complete, the area of a room with visible sky should ideally be 0.8 times or more of the former area on the working plane prior to the development. If not tested, state that you do not have confirmed room layouts for the neighbouring properties.

The BRE Report also recommends a review of the surrounding external amenity spaces such as gardens, parks or playgrounds. The analysis should confirm whether at least 50% of the area of each amenity space should receive at least 2 hours of sunlight on 21st March. Alternatively, if an existing garden or amenity space remains no less than 0.8 times its former value, then the loss of light to this space is unlikely to be noticeable. The availability of sunlight should be checked for all open spaces where sunlight is required. 

Analysis for rooms within a proposal

VSC, APSH and 2 hour Sunlight to Amenity tests are also applied to proposed developments. However, the DD analysis is substituted by the Average Daylight Factor (ADF). 

The ADF recommendations are set out in the BRE guide and are based on British Standard BS 8206 Part 2 and the Chartered Institute of Building Services Engineers Applications Manual on window design. The calculation measures the distribution and quality of light within a room served by a window. It takes account of the size of the room, the size and number of windows, surface finishes, glazing qualities and room use. If a room is served by more than one window, the total ADF for that room will be based on the aggregate amount of natural light entering the room through all of the windows. Where supplementary lighting is supplied the following ADF values should be considered the minimum. 2% for rooms containing a kitchen element, 1.5% for living rooms and 1% for bedrooms.

Mitigation factors

It is of vital importance that as well as Local Plan policy, the surrounding context is taken into account when considering the results. The target values are guidelines only and therefore it’s often not a case of a pass or a fail. Some LPAs advocate comparable analyses of the results against similar developments in the locality and often it is a challenge to either obtain this data or to be able to compare it fairly. Each case is therefore quite independent and often will benefit from the early engagement of a consultant to review and advise upon the emerging proposals.

Solar dazzle and glare

Also think about a building’s materials palette. Will this cause any form of solar glare or dazzle for neighbouring properties or for road or rail users? If so then a rethink is required before submission of an application. Again, analyses can be taken using a 3D model to highlight where light will be reflected based upon the materials used. 


So, a lot to consider on a complex and nuanced subject,  but hopefully this provides an initial insight into why, when and how to assess the impact of a development proposal on light. As we are striving for high quality, well-functioning development, the impact of light on both new development and its neighbours should not be underestimated and must be well considered. This is a technical area and way beyond our planning capabilities, so our advice is to check out the BRE Report 209: Site layout planning for daylight and sunlight: a guide to good practice and add a Daylight/Sunlight consultant to your design team ASAP.