Horizontal boundaries deal with the ownership of space above and below a property, as opposed to vertical boundaries which are more traditionally defined by reference to maps and plans. Horizontal boundaries often matter most in flats, basements, roof spaces, and overhangs. The recent case of Khosa & Anor v Ganesarayan & Anor [2026] EWHC 662 (Ch), shows how unclear boundaries can trigger costly disputes.
Horizontal boundaries are one of those property law issues that sound abstract until they suddenly are not. A loft conversion next door. A basement excavation. A question about who owns the roof, the soil, or the void in between. At that point, lines on a plan stop being helpful, and the detail really matters.
What is a horizontal boundary (and why isn’t it just common sense)?
In simple terms, a boundary is not always vertical. We are all familiar with the idea that a boundary runs along the ground. A line between two gardens, marked out by a fence, wall or hedge.
A horizontal boundary, by contrast, separates ownership vertically. It defines the edge of the boundary both above and below the vertical plane. Issues with horizontal boundaries can often arise in the following examples:
- A building has been split into flats
- There is a basement under one property but supporting another
- A flying freehold exists (where part of a building overhangs or underlies another)
English law does not automatically assume that ownership goes ‘from the heavens to the centre of the earth’. In fact, the reality is far more nuanced. Instead, ownership depends on what the title documents say, how the property has been used, and, sometimes, what the courts think the parties must have intended.
Problems can arise in circumstances where title plans lack clear vertical descriptions (as is often the case) and rights of support, shelter, and access are poorly defined or not defined at all. In such cases, assumptions can appear based on habit rather than ownership
What did Khosa v Ganesarayan tell us about horizontal boundaries?
The case of Khosa & Anor v Ganesarayan & Anor is a useful reminder that courts will look closely at what exactly was demised (legally granted) in a property title.
Although every case turns on its facts, the dispute centred on competing claims over parts of a building divided horizontally. A dispute arose concerning air conditioning units installed in a roof space by one of the parties. The question then became where did the ground floor level end and were the units trespassing into the airspace above?
The High Court’s approach was cautious. Rather than defaulting to assumptions about convenience or fairness, it focused on the precise language used in the transfer, the structure of the building and whether rights over adjoining space had been expressly granted. The Judge concluded that the horizonal boundary does not just extend up and down a straight line and that it can in fact undulate, just as a vertical boundary can.
Practical steps to avoid boundary disputes
You cannot fix every historical ambiguity, but you can reduce risk.
If you’re buying:
- Scrutinise title plans and wording beyond the red line
- Ask specific questions about roofs, basements, and structural elements
- Be cautious with phrases like “including all parts of the building”
If you’re developing:
- Do not assume ownership gives you unfettered building rights
- Check for express rights of support, shelter, and access
- Resolve queries before works begin, not after scaffolding goes up
If you’re already in dispute:
- Pause before escalating
- A clear legal analysis can often defuse assumptions on both sides
A final thought
With pressure on space, especially in towns and cities, property owners are increasingly looking upwards and downwards, not just sideways. Basement extensions, roof terraces and air-source heat pumps fixed to shared structures can all result in questions being raised over horizontal ownership. Older titles were never drafted with this level of intensification in mind and that mismatch is where today’s disputes are born.
Horizontal boundary disputes are rarely about bad neighbours. More often, they are about optimistic assumptions meeting stubborn paperwork. The law does not punish ambition, but it does insist on clarity. Knowing where you stand, quite literally, is one of the most valuable pieces of advice we can give.
Annabel Meyer is a Senior Associate in our disputes team. The team deal with both personal and business disputes with specific expertise in property. If you require legal support with any issues covered in this article, please contact the team: Property Dispute Solicitor for Individuals | Greene & Greene.
This is only intended to be a summary and not specific legal advice.
