Building Regulation B1

Designing An Escape Window

Fire is a dynamic event which, if unchecked, will spread rapidly throughout a dwelling eventually putting all people present at risk. Recent building regulation changes aim at reducing the risks, if fire occurs, in new or altered houses by including early warning and appropriate means of escape in a building’s design.

In a typical one or two storey house, loft conversion or basement, regulation B1 can often be met by the provision of ‘emergency egress windows’ (i.e. escape windows).

This note is intended to help in the design of an escape window, which complies with the requirements of regulation B1.

It must have an unobstructed opening of at least 0.33m² in area, subject to minimum dimensions, (see table 1) The opening window can be top, side or centre hung, or sliding, The opening can be at an angle rather than straight through. For example the window may have a hinge system that reduces the actual width, or height, of the clear opening available. In this case the minimum opening size is measured at an angle between the frame and the fully opened window element. The bottom of the opening must be no more than 1100mm and not less than 800mm above the internal floor level. ( 600mm for a window in a roof) The opening window can be top, side or centre hung, or sliding. It should be immediately available for use by escaping people. It should be positioned to allow an escaping person to reach a place of safety from a fire.

Escape windows from a basement, ground and first storeys provide means for self-rescue, and it is not unreasonable for people to escape across a pitched roof for example.

At a higher level (i.e. loft conversion prior to 2007), escape from an escape window normally depends on a ladder being set up which immediately imposes additional design requirements:

For a window in a roof the bottom of the opening must be a maximum of 1700mm measured from the eaves. For a dormer, a maximum of 1700mm measured on the roof surface, from the eaves to the vertical plane of the dormer. It must be located to allow safe ladder rescue from the ground. Suitable pedestrian access must be available to a point at which a ladder can be carried and set for rescue.

The recommended safe angle of a set up ladder is 75° (1:4). The effect of an extension on the ability to escape from windows in other parts of the house, especially from a loft conversion, must be considered at the design stage.

(Table 1) Ratio of dimensions that give a clear opening size of 0.33m²