Borough Council of Wellingborough

Smokefree England

What does 'substantially enclosed' mean?

A premise or structure will be considered substantially enclosed if it has a ceiling or roof  but there is an opening or aggregate area of openings in the walls which is less than half of the total area of the walls, including other structures that serve the purpose of walls and constitute the perimeter of the premise. This is called the '50% rule'. When determining the area of an opening, no account can be taken of openings in which doors, windows or other fittings can be open or shut. A roof includes any fixed or moveable structure or device, such as a retractable canvas awning, capable of covering all or part of the premises.


The definition includes temporary structures such as tents and marquees.


For an example of how to calculate the 50% rule visit