The pressure to densify urban areas without sprawling further into greenbelt land has given rise to a new era in city development – upward expansion. Commonly referred to as ‘Airspace developments’, these projects are becoming increasingly popular, particularly in London, as developers aim to unlock additional value by building more storeys on top of existing structures (apartment blocks, retail units, offices, etc).
However, as the skyline evolves, so too do the legal risks. One of the most significant, and often underestimated, is the right to light.
What is a right to light?
The ‘right to light’ is the rule which entitles a building to receive a certain level of natural light through its windows. It shouldn’t be confused with a more general right to sunlight or daylight, instead ‘right to light’ is a specific legal entitlement to a sufficient level illuminance within a defined internal space (as determined by expert analysis).
During the planning stages of a development, daylight and sunlight will be assessed under guidelines published by the Building Research Establishment (BRE). These BRE standards are commonly used in planning applications and environmental impact assessments to gauge whether new developments might adversely affect neighbouring properties.
The key difference here is that these are merely planning considerations, and are not legally binding rights. ‘Right to light’, however, once established, is enforceable in court.
This distinction is critical for airspace developments. A scheme may receive planning permission from the local authority after passing daylight and sunlight tests, but still face private legal challenges if it infringes a neighbour’s ‘right to light’, for example.
How are rights to light acquired?
Most rights to light arise through long-term use under the Prescription Act 1832. If a window has received uninterrupted natural light for at least 20 years, the owner of the benefiting property may acquire a right to that light, even if there is no express grant in the title deeds. These rights attach to the land and are enforceable against future owners.
Developers must therefore assess whether neighbouring buildings might have acquired such rights before proceeding with upward extensions. The fact that the development is within the developer’s own building footprint does not exempt it from risk as light to lower-storey flats or adjoining properties could still be adversely affected.
How is loss of a right to light measured?
A ‘right to light’ doesn’t entitle a property owner to unlimited daylight, the law protects only the reasonable amount of natural light needed for the normal use of a room. Establishing whether that threshold has been crossed is a technical exercise, typically involving what’s known as the Waldram method. This technique assesses how much of the sky is visible from a defined point inside the affected room – usually a spot around 850mm above floor level and about a metre back from the window. If too little sky remains visible, the light may be deemed inadequate.
One commonly used benchmark is the Vertical Sky Component (VSC), with 27% often cited as the level below which discomfort begins. But legal analysis doesn’t stop there. The courts take a more pragmatic view. They will ask whether the loss has materially affected the room’s function. A lounge or kitchen left gloomy and hard to use will raise red flags, while reduced light in a storage cupboard may not.
This blend of geometry and judgement makes light analysis a grey area – both literally and legally. For developers, particularly those adding rooftop extensions, the key is to commission expert light modelling early in the process to understand where risks lie and which neighbouring properties might raise objections.
Remedies for infringing a right to light
When a new structure interferes with a neighbour’s established ‘right to light’, the courts can intervene – sometimes dramatically. The most forceful remedy is an injunction, which could compel a developer to halt construction or even remove the offending section, no matter how far along the build is. In the well-known case of Regan v Paul Properties, the court ordered just that, emphasising that monetary compensation won’t always be enough.
However, in many situations the court will award damages instead, especially where the loss is modest, the impact less severe, or the project substantially complete. These damages aren’t based on the neighbour’s loss, but rather on a share of the developer’s gain. The usual range is around 1% to 3% of the anticipated profit, though the precise figure depends on the circumstances.
A third option is declaratory relief, which allows developers to ask the court in advance for a ruling that the scheme won’t breach anyone’s rights. While potentially helpful, this is a strategic route that demands careful timing and thorough evidence.
The risk of an injunction, even late in the day, can upend a project. This is particularly relevant in airspace developments, where neighbouring windows are often close by and the margin for error is slim. Early legal advice, proper modelling, and a robust risk management strategy are essential.
What is right to light insurance?
To mitigate the risks, many developers turn to ‘right to light’ insurance. This specialist cover protects against claims from third parties alleging loss of light. It typically covers:
- Legal costs of defending a claim;
- Damages or settlement sums;
- Potential losses from delay, redesign or demolition;
- Loss of sale or refinancing opportunities if legal action clouds title.
Premiums vary depending on the risk profile of the development. Some insurers may exclude cover if early engagement with affected parties has already taken place or if a formal objection has been raised.
However, insurance is not a panacea. While it provides financial protection, it does not stop an aggrieved neighbour from seeking an injunction. Many developers therefore use it alongside proactive negotiation or legal strategies, such as attempting to extinguish rights via Section 203 of the Housing and Planning Act 2016 (where public land is involved), or through careful architectural design that reduces impact.
Take it seriously
‘Right to light’ are a critical, and complex, legal consideration in airspace and rooftop developments. They represent a private property right enforceable in court, distinct from and independent of planning controls. With the trend towards vertical expansion continuing, especially in dense urban locations, developers must balance commercial ambition with meticulous legal and technical assessment.
At Buckles Solicitors, our commercial property and planning specialists work closely with surveyors, insurers, and developers to manage ‘right to light’ risk and deliver viable airspace schemes. If you’re considering building upwards, we can help you assess, mitigate, and navigate the legal landscape.
