Guest Expert: Daylight and Sunlight Assessments – A Battle Between Light and Dark

Monday, October 9, 2017

Ian McKenna is a chartered surveyor and partner at Malcolm Hollis, where he’s worked for nearly 20 years. During this time, he’s specialised in rights of light law and daylight and sunlight assessments. Ian is our go-to authority on all matters related to daylight, and was instrumental in the success of our Crescent Road project.

When local authorities look at your planning application, they will often ask your architect or designer to support the application with a smorgasbord of technical reports.

If you’re building nearby existing residences – whether they’re houses, flats or tower blocks – one of these reports will usually be a daylight and sunlight assessment, which demonstrates the impact your proposals would have on the amount of daylight and sunlight those surrounding dwellings currently enjoy.

If you’re developing a house, chances are you’re doing it to increase your available space and the value of the property. This makes it very likely that a development of any significance will impact the daylight and sunlight of any surrounding dwellings, especially in London where houses are often tightly packed together.

As daylight and sunlight assessments are highly detailed and technical, most architects don’t take them on themselves and will instead bring in consultants such as myself to take care of it for them. Every project and the site it sits on is entirely different: a two-storey rear extension might be acceptable if it only blocks light to secondary windows of a neighbouring property, but is more likely to be refused if it casts significant shadow over the living rooms of neighbouring dwellings.

Daylight and sunlight assessment can make or break your development

Daylight is a sensitive subject and a common source of neighbour objections which often bleeds over into other concerns, such as if a view they currently enjoy will be blocked or if they find your development too overbearing. I represent both developers and objectors in my line of work and, either way, will assess the situation objectively rather than appeal to the vested interests of either party.

After all, you can’t argue with the sun. The first half of our job is 100% scientific, using bespoke software and sophisticated scanning equipment to develop a detailed 3D model of the current structure, the proposed development, surrounding structures and the landscape. We then simulate the direction and occlusion of daylight and sunlight through 365 days of the year to provide a near-perfect simulation of how daylight in the area will be affected by your development.

This hard data is then balanced against the benefits of the development and any factors that might mitigate any negative impact to surrounding dwellings. In the end, we present a balanced and objective assessment of the development and its impact to help planners reach a fair verdict.

Planning departments refer to the BRE (Building Research Establishment) guide to determine whether the development conforms with the best practice for the target levels of daylight. They will request a daylight and sunlight assessment if there is any potential impact to neighbours, so you may as well have one prepared in advance so that you’re aware of the risks your application faces.

In fact, not having a daylight consultant involved from early on can make or break a project. By having a daylight and sunlight consultant on board at an early stage, your architects or designers can have an early assessment of daylight impact so that they can take it into account during the design phase, or at least be prepared for the issues it might raise during planning and find ways to mitigate the impact to the neighbour’s amenity.

The alternative is that you spend time and money drawing and submitting plans that are rejected because of their impact to the neighbour’s light, forcing you to either go back to the drawing board or abandon your plans entirely.

Let there be light!

The original property on Crescent Road projected deep into the garden, casting a shadow on the neighbour’s home.

The new build, though larger overall, provided the neighbours with more daylight.

In rare cases, daylight impact isn’t something that you have to work around and can instead provide a positive case for the development.

Crescent Road was one such project, as although the new house on the site would be far larger than the existing one, because it was taller and shorter than the existing low and long cottage that projected further into the garden, the development would actually increase the amount of sunlight passing into the neighbour’s home – as is demonstrated in the pictures above.

This sweetened the deal for the neighbours, who had previously objected to development on the site. It’s rare that our assessments go in this direction, but it is an example of how – through smart design – you can occasionally use daylight and sunlight assessments to your favour.

If you have any questions about daylight and sunlight assessments or right to light law, feel free to get in touch with our firm at [email protected] and we’ll be happy to help, whether you’re working on a project yourself or are concerned about a development nearby.

Malcolm Hollis can be found at