Extending near a boundary: rights of light, overlooking and neighbour consultation in practice
Boundary proximity is where extensions generate objections. Here's what right to light actually protects, what counts as overlooking versus what doesn't, and how to handle neighbour consultation so a reasonable scheme doesn't turn into a dispute.
Extensions near a boundary run into two separate concerns that get talked about as though they're the same thing: right to light, which is a legal property right, and overlooking, which is a planning consideration. Confusing the two leads to worrying about the wrong one at the wrong stage.
Right to light is a legal right, separate from planning
An easement — often acquired automatically after twenty years of uninterrupted light through a defined window — protects a minimum level of light to existing windows. It's assessed technically, commonly with the 45-degree rule as a rough initial check and a full geometric assessment where it matters, and it exists independently of planning permission. That means a scheme can hold full planning consent and still infringe a neighbour's right to light, exposing the build to an injunction or a damages claim regardless of what the planning department decided.
Overlooking is a planning consideration, not a legal right
Unlike right to light, there's no legal right to privacy from being overlooked. Planning policy and case officers weigh loss of privacy heavily nonetheless, generally using a rule-of-thumb separation distance between facing habitable room windows — commonly cited around 21 metres for two-storey properties facing each other, though this varies by authority and isn't a fixed national rule — as a starting point for assessment rather than a strict cut-off.
Obscure glazing and non-opening windows as a planning tool
A common mitigation for a side elevation close to a boundary is obscure glazing with a fixed or high-level opening only, specifically to address overlooking without needing to move the whole extension. Understanding this early can avoid designing something that gets refused for a reason a glazing specification would have resolved from the outset.
What the 45-degree and 25-degree rules actually check
These are quick daylight and sunlight screening tests some authorities apply, measured from a neighbour's window toward the proposed extension, rather than universal legal thresholds. They're useful as an early self-check on a design before submission, but they're not determinative on their own — a scheme can fail one of these rough tests and still be acceptable, or pass it and still raise a genuine light or amenity concern that needs addressing on its own merits.
Talking to the neighbour before the site notice arrives
As with planning applications generally, most objections that are really about not having been told, rather than about the scheme's actual merits, are avoidable with a conversation before formal notification. This is worth doing specifically where a design already touches on overlooking or light, since an unexplained proposal in that territory reads as considerably more threatening than one the neighbour has already heard about directly.
When it's worth commissioning a formal right to light assessment
For anything close to a boundary with existing windows nearby, particularly where planning consent alone won't protect against a civil claim, a proper technical assessment before construction — not after a neighbour complains — is the only way to genuinely know the exposure rather than hope it isn't significant.