Daylight & Sunlight Assessment Background

As a party applying for planning permission, you may be asked by the Local Authority to provide a Daylight and Sunlight Assessment to explain to those assessing the application, the implications regarding how the proposed development might impact upon the light to neighbouring properties.

Assessment Criteria

The most common methodology for assessing daylight and sunlight impact, is set out in the document known as “Site Layout Planning for Daylight and Sunlight – A Guide to Good Practice, 2nd Edition”.  It is often known as BRE 209.

Many (albeit not all) Local Authorities state in their policies, Validation Checklists or supplemental design guides, that daylight and sunlight will be assessed in accordance with such guidance.

Such assessments are usually carried out by consultants who use specialist software, combined with 3D computer models, to calculate the results of the tests contained in the BRE Guide.

What are the tests?

When assessing the impact on daylight and sunlight to neighbouring properties, the BRE Guide considers the following tests:

  • Vertical Sky Component Test (VSC)
  • No Sky Line Test to consider Daylight Distribution (if neighbour’s room layouts are known)
  • Annual Probable Sunlight Hours Test 
  • Assessment of Outdoor Amenity Areas (if applicable)

It is particularly important to note that the first two tests above relate to daylight, and that ideally, both tests should be done, although there are occasions when undertaking the daylight distribution test is not possible, when neighbouring room layouts are not known.  If room layouts are known, the BRE does consider that both VSC and the No Sky Line tests should be carried out.  

We commonly see poorly prepared reports that do not fully consider the full requirements of the BRE Guide, leaving the developer at risk of delays due to the report being considered inadequate, and having to be re-done by others.

Who Can Carry Out These Daylight and Sunlight Reports for Me?

There are different groups of professionals who typically tend to provide daylight and sunlight assessments to assess the impact on neighbouring properties.  These are listed below:

Any of the above should be capable of preparing a Daylight and Sunlight Assessment, if they have a) appropriate software that meets all of the tests in the BRE Guide and b) relevant experience to interpret and report upon the results data.

We often come across ‘assessments’ that are based upon free software or ‘apps’ that only provide basic sun path information.  These commonly most provided by smaller architectural practices, or even the applicant themselves, however, such studies do not cover the tests laid down in the BRE Guide.  Provision of a study that does not cover all the necessary components can cost money and waste time.

We have had many instances where developer clients have come to us having firstly commissioned a ‘basic’ assessment by another party, only to find later in the day that it is not suitable for the Local Authority planning team dealing with the application, hence causing delay and extra cost to start the process over again.

Finally, in some instances, daylight and sunlight assessments prepared by the designer have the potential to be questioned regarding a conflict of interest; is the report ‘glowing’ because the results pass the BRE Guide tests with flying colours?  Or could it be difficult for a designer to highlight and report independently on matters of daylight and sunlight where the design falls sort of compliance?

What About Assessments That Do Satisfy the BRE Tests?

As above, we often come across well-prepared Daylight and Sunlight Assessments carried out by either Mechanical Engineering Consultants or Planning Consultants, and, in such circumstances, the service can ‘tick’ the relevant planning box and enable the application to proceed smoothly. 

However, in addition to planning related considerations regarding daylight and sunlight, many developers also need to be mindful of potential civil constraints, surrounding the matter of ‘legal right to light’.  These are potentially very onerous matters that are completely separate to the planning system. Even with planning permission, if a neighbour has a legal right to light, and your development causes sufficient loss of light, you may not be able to build what you have planning consent for, and, failing an injunction, you may be left with potentially large compensation costs that could make the scheme financially unviable.

So, Why Does My Daylight and Sunlight Assessment Not Cover Right to Light?

Right to Light is a specialist area of law.  Planning considerations do not consider legal easements, and as such, it is often the case that schemes sail through planning, but do not consider legal constraints. 

Can My Daylight and Sunlight Consultant Advise Me on Legal Right to Light Matters?

Not necessarily.  Right to light is a complex matter and considers different assessment criteria to that used in planning considerations.  Very few professionals other than those who are Right to Light Consultants have the software, and understanding of the legal matters and case law, to be able to advise on such matters.

What Does This Mean for Me?

It means that if your Daylight and Sunlight Assessment has been prepared by a party such as a firm who specialise in say, mechanical engineering or planning consultancy, they may not have the software or ability to carry out the legal right to light assessment for you, if required.

If your scheme has absolutely no risk of there being a right to light issue, for example, if the scheme involved a new build property directly next to another new build, that had no legal rights, then this may not matter.

However, in our experience, many new builds or extensions are often located close to existing properties that do have legal rights; the most common situation being where neighbouring buildings have windows that are over 20 years of age.

In such a situation, you really may need to assess the legal right to light risk.

If you advisor who has prepared your daylight and sunlight assessment for planning cannot assist you with this, then in effect, you are then going to have to commission a right to light consultant, who will need to start from scratch.  This will most likely cost you more in fees and take longer than had you commissioned a party who could provide both a daylight and sunlight report for planning, AND a legal right to light assessment from the outset.

In Summary

If you are commissioning a neighbouring daylight and sunlight to help you with your planning application, make sure that:

  • The firm you appoint can carry out all of the BRE Guide tests (not just some of them)
  • The firm you appoint can, if required, provide a legal right to light assessment.

Not doing so can lead to delays and false economy, meaning you can incur larger fees in the long run.

If you are a developer, or a developer’s agent, and you are in need of advice on such matters, we would be pleased to assist.  Please do contact us on [email protected]

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