Right to Light London: How It Affects Your Extension
Right to light is one of the most misunderstood aspects of extending a London home. Your neighbour can potentially block your extension or claim compensation, even after you have received planning permission. Here is what every London homeowner needs to know.
Quick Answer
Right to light is a separate legal right from planning permission. A neighbour with 20+ years of uninterrupted light can claim an injunction or compensation if your extension significantly reduces their daylight. A professional daylight assessment costs £800-3,000 and is essential for two-storey extensions near boundaries.
£800-£3k
Assessment Cost
£1k-£5k
Insurance
20+ years
Legal Right
Check your specific property constraints
Free Property CheckWhat Is Right to Light?
Right to light is an ancient common law right that gives a property owner the right to receive natural daylight through defined windows or apertures. It is primarily governed by the Prescription Act 1832, which establishes that if a window has received natural light for 20 years or more without interruption, the owner acquires a legal right to continue receiving that light.
This right exists independently of the planning system. It is a private legal right between property owners, which means that obtaining planning permission for your extension does not protect you from a right to light claim. The two operate in completely separate legal frameworks.
In London, where properties are built close together and many homes are over 100 years old, right to light is a real and frequently exercised right. It is particularly relevant for terraced and semi-detached houses where extensions can significantly reduce daylight to neighbouring windows.
How Right to Light Affects Your Extension
When you build an extension, it may block some of the natural light that currently reaches your neighbour's windows. If that reduction is significant enough, your neighbour can take legal action. The consequences can be severe:
- Injunction: A court order requiring you to demolish or modify the offending structure. This is the nuclear option and courts do grant it, though it is relatively rare
- Damages: Financial compensation to the affected neighbour, typically based on the reduction in their property value. Can range from a few thousand pounds to tens of thousands
- Construction delays: Even the threat of a claim can cause your builder to stop work while the dispute is resolved
- Legal costs: Defending or settling a right to light claim can cost £5,000-50,000+ in legal fees alone
The 45-Degree Rule Explained
The 45-degree rule is a simple test used by planning officers (and informally by architects and neighbours) to assess whether an extension will cause an unacceptable loss of light. It is not a legal test for right to light claims, but it is a useful first indicator.
The test works like this: draw a line at 45 degrees from the centre of the nearest window on the neighbouring property, both in plan (looking from above) and in elevation (looking from the side). If your proposed extension falls within the 45-degree line, it is likely to cause a noticeable reduction in daylight.
How to Apply the 45-Degree Rule
- Step 1: Identify the nearest habitable room window on the neighbouring property (bedrooms, living rooms, kitchens count; bathrooms and hallways usually do not)
- Step 2: On your floor plan, draw a 45-degree line from the centre of that window towards your proposed extension
- Step 3: On the side elevation, draw a 45-degree line from the centre of the window upwards towards the top of your extension
- Result: If your extension projects beyond either 45-degree line, it will likely reduce daylight to that window noticeably
Important limitation: The 45-degree rule is a planning tool, not a legal test. Passing the 45-degree test does not mean you are safe from a right to light claim. Equally, failing it does not automatically mean a claim will succeed. For legal certainty, you need a professional BRE-compliant daylight and sunlight assessment.
Check if you need planning permission
Get an instant assessment of your permitted development rights. See conservation areas, Article 4 directions, and planning constraints.
BRE Daylight and Sunlight Guidelines
The BRE (Building Research Establishment) guidelines are the industry standard for assessing daylight and sunlight impact. They provide three key metrics that planning officers and courts use to evaluate whether a development causes an unacceptable loss of light.
Vertical Sky Component (VSC)
Measures how much sky is visible from the centre of a window. A VSC of 27% or more is considered adequate. If the proposed development reduces the VSC to below 27%, or reduces it by more than 20% of its current value, the impact is considered noticeable.
Annual Probable Sunlight Hours (APSH)
Relevant for windows facing within 90 degrees of due south. A window should receive at least 25% of annual probable sunlight hours, with at least 5% in winter months. Reductions beyond these thresholds trigger concern.
No-Sky Line (NSL)
Maps the area within a room from which the sky can be seen through the window. If the no-sky line moves inward so that a significant part of the room cannot see the sky, the daylight distribution is considered adversely affected.
When You Need a Daylight and Sunlight Assessment
Not every extension requires a formal assessment. Here are the situations where you should seriously consider commissioning one.
- Two-storey extensions: The additional height significantly increases the shadow cast on neighbouring properties
- Extensions near boundaries: Building within 2-3 metres of a boundary with habitable windows opposite
- Neighbour objections: If a neighbour has already raised light concerns, a professional report strengthens your planning application
- Planning requirement: Some London boroughs require a daylight/sunlight report as part of your planning application, especially for larger extensions
Cost: A professional BRE-compliant daylight and sunlight assessment typically costs £800-£3,000 depending on the number of neighbouring windows assessed and the complexity of the site.
Concerned about right to light?
Check your property's planning constraints instantlyCommon Right to Light Scenarios in London
Terraced Houses
The most common scenario for right to light disputes. Rear extensions on terraced houses can block light to the side-facing windows of neighbouring kitchens and living rooms. Two-storey rear extensions are particularly problematic as the additional height creates a much larger shadow.
Basement Lightwells
Many London Victorian and Edwardian houses have basement-level rooms that rely on lightwells for natural light. If your ground-level extension extends over or adjacent to a neighbour's lightwell, you could significantly reduce the already limited daylight to their basement room.
Loft Dormers
Dormer windows on loft conversions are generally less affected by right to light issues because they sit above the roofline. However, a large dormer can still cast shadows on neighbouring dormer windows, particularly on closely spaced terraced properties where roof slopes face each other.
Right to Light vs Planning Permission: They Are Separate
This is the single most important point in this article. Planning permission and right to light are entirely separate legal matters. Getting planning approval does not give you the right to infringe your neighbour's right to light.
The planning authority assesses your proposal against planning policy (amenity, character, design). Right to light is a private legal right between property owners, enforceable through the civil courts.
You can receive full planning permission and still face a successful right to light claim that requires you to pay compensation or, in extreme cases, modify or demolish part of your extension.
What to Do If a Neighbour Raises Right to Light Concerns
Early engagement with neighbours is the best strategy for avoiding right to light disputes. Most claims are settled through negotiation rather than court action.
- Engage early: Talk to your neighbours about your plans before you submit a planning application. Show them the drawings and listen to their concerns
- Commission a daylight report: If there is any doubt, invest £800-3,000 in a professional assessment. This gives you objective data to discuss
- Offer design modifications: Small changes like stepping the extension away from the boundary, reducing height, or using a flat roof instead of pitched can significantly reduce light impact
- Negotiate compensation: In some cases, a modest financial payment (a few thousand pounds) can resolve a claim far more cheaply than legal proceedings
- Consider mediation: If direct negotiation stalls, a professional mediator can help both parties reach agreement without the cost and stress of court
Free AI Assistant
Ask anything about right to light and extensions
Right to Light Insurance
If there is a risk of a right to light claim but you want to proceed with your extension, you can take out a right to light indemnity insurance policy. This covers the legal costs and any compensation that might be awarded against you.
- Cost: £1,000-£5,000 one-off premium depending on the assessed risk level and sum insured
- Cover: Typically covers legal defence costs plus compensation awards, usually up to £250,000-£500,000
- Requirement: The insurer will usually require a daylight assessment to evaluate the risk before issuing a policy
- Limitation: Insurance does not prevent a claim. It covers the financial consequences, but you may still need to deal with the stress and disruption of legal proceedings
Practical advice: Right to light insurance is most commonly taken out for two-storey extensions and basement developments in densely built-up areas of London. For single-storey rear extensions under Permitted Development, the risk is typically low enough that insurance is not necessary, provided you stay within PD height limits.
Frequently Asked Questions
Can my neighbour stop my extension because of right to light?
Potentially, yes. If a neighbour can demonstrate they have a right to light (typically 20+ years of uninterrupted light to a window) and your extension would significantly reduce that light, they can seek a court injunction to prevent or modify the extension, or claim financial compensation. However, injunctions are relatively rare for residential extensions. Most disputes are resolved through negotiation or modest compensation payments.
Does right to light apply to Permitted Development extensions?
Yes. Right to light is a private legal right that applies regardless of whether your extension has planning permission, uses Permitted Development rights, or has Prior Approval. The planning system and right to light law are completely separate. A PD extension that significantly blocks a neighbour's light can still face a right to light claim.
How much does it cost to defend a right to light claim?
Legal costs for defending a right to light claim range from £5,000 for straightforward cases settled early through negotiation to £50,000+ for cases that proceed to court. The average settlement for residential right to light claims in London is typically £3,000-£15,000 in compensation, plus legal costs. This is why many homeowners prefer to negotiate early rather than litigate.
Do new-build windows have right to light?
No. Right to light under the Prescription Act 1832 requires 20 years of uninterrupted light enjoyment. Windows installed less than 20 years ago have not yet acquired the right. This means if your neighbour recently built an extension with new windows facing your property, those windows do not yet have a right to light that could affect your development plans.
Can I get right to light insurance after starting construction?
It becomes much harder and more expensive to obtain right to light insurance once construction has started, especially if a neighbour has already raised objections. Insurers assess the risk before the development begins. If a claim is already threatened, most insurers will decline to provide cover. Always arrange insurance before breaking ground if you believe there is a risk.
Does the 45-degree rule guarantee I am safe from a claim?
No. The 45-degree rule is a planning assessment tool, not a legal test for right to light. Passing the 45-degree test reduces the likelihood of planning objections on daylight grounds, but it does not protect you from a private right to light claim. Only a full BRE-compliant daylight and sunlight assessment can give you a more reliable picture of whether a claim might succeed.
Summary: Right to Light and London Extensions
What it is: A legal right allowing property owners to receive natural light through windows that have enjoyed 20+ years of uninterrupted light. Governed by the Prescription Act 1832 and enforced through civil courts.
Key risk: Right to light and planning permission are separate. You can get planning approval and still face a successful right to light claim that requires compensation or modification of your extension.
When to worry: Two-storey extensions, builds near boundaries with habitable windows opposite, and projects where neighbours have already raised concerns. Single-storey PD extensions rarely trigger successful claims.
Best strategy: Engage with neighbours early, commission a daylight assessment (£800-3,000) if there is any doubt, and consider right to light insurance (£1,000-5,000) for higher-risk projects. Prevention and negotiation are always cheaper than litigation.
Ready to start?
Check your extension's light impact
Our AI assistant can help you understand whether your extension may trigger right to light concerns and what steps to take. Free to use, no obligation.
Or email hello@mayfairstudio.co.uk · 07405 920944
Related Articles
Party Wall Agreement London: Complete Guide
Everything about party wall agreements in London. Costs, process, timelines, and what happens if your neighbour dissents.
Planning & RegulationsExtension Rejected? Appeals Guide London
What to do when your planning application is refused. Appeal process, success rates, and how to strengthen your case.
ExtensionsTwo-Storey Extension London: Complete Guide
Costs, planning rules, design options, and practical considerations for two-storey extensions in London.