Glossary
Oversailing a neighbour's land on a London extension
Construction that crosses a neighbour's boundary or air-space. Requires consent.
Construction that crosses a neighbour's boundary or air-space. Requires consent.
An oversail is any part of a structure projecting over a neighbouring property or the public highway — a gutter, eaves, foundation footing or scaffold. There is no right to oversail: doing it without agreement is a trespass, and it is one of the most common causes of dispute on a London infill extension.
Building right up to a boundary, the gutter and fascia commonly project 100 to 150 mm beyond the wall face. A traditional strip foundation projects further still — typically 150 mm each side of the wall. Scaffolding needed to build the flank almost always stands on the neighbour's land.
The practical answers are a concealed or secret gutter, a parapet detail that keeps the roof edge within the boundary, and an eccentric or piled foundation that keeps the projection on your own side.
Only partly. Section 6 covers excavation near a neighbour's structure and section 2 covers work to a party structure, but neither gives a right to project into airspace. An oversail licence — a short written agreement, often with a fee — is the correct instrument, and a crane oversail licence is standard practice.
The boundary line should be drawn accurately on the site plan and the roof edge detail drawn at 1:5 showing the gutter position relative to it. Where a foundation must stay within the boundary, that decision belongs at design stage — retrofitting it after the engineer has sized a strip footing is expensive.
Oversail in a Hillingdon context: London Borough of Hillingdon (Hillingdon Council) runs 29 conservation areas including the Uxbridge Conservation Area and the Ruislip Village Conservation Area, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. That decides how oversail is handled: £548 and 8 weeks for a Hillingdon householder application, or £274 for the Lawful Development Certificate that records oversail as lawful. The law behind oversail sits in the Town and Country Planning Act 1990, the GPDO 2015 and the Building Regulations 2010.
| Legal character | Trespass without agreement |
|---|---|
| Typical gutter projection | 100–150 mm |
| Typical strip foundation projection | 150 mm each side |
| Correct instrument | Oversail licence |
| Party Wall Act | Does not confer a right to oversail |
| Design responses | Secret gutter, parapet, eccentric or piled foundation |
Not without their written agreement. It is a trespass regardless of how small.
It permits access for notifiable works in defined circumstances, but not a general right; a licence is safer.
Design a parapet or secret gutter and an eccentric foundation from the outset.
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