Understanding Approved Document B – Fire Safety




Approved Document B covers fire safety matters within and around buildings. The document outlines particular requirements and examples of solutions for some of the more common building situations.

It is published in two volumes, 

  • Volume 1: It deals solely with dwellings (houses), including blocks of flats, 
  • Volume 2: deals with all other types of building cover by the Building Regulations, apart from dwellings/houses.

This blog post aims to highlight the fire safety regulations concerning architectural glazing and fenestration like windows and external doors in residential buildings.

Volume 1 of Approved Document B

Approved Document B, Volume 1, lays out the guides for fire safety in dwellings. 

Section 2 : Means of escape – dwellinghouses

Escape from the ground storey

2.1 All habitable rooms (excluding kitchens) should have either of the following: 

  • an opening that directly on to a hall leading to a final exit, 
  • an emergency escape window or door, as described in paragraph 2.10.

Escape from upper storeys a maximum of 4.5m above ground level

2.2 See Diagram 2.1b. Where served by only one stair, all habitable rooms (excluding kitchens) should have either of the following.

  1. An emergency escape window or external door, as described in paragraph 2.10.
  2. Direct access to a protected stairway, as described in paragraph 2.5a.

2.3 Two rooms may be served by a single window. A door between the rooms should provide access to the window without passing through the stair enclosure. Both rooms should have their own access to the internal stair.

Emergency escape windows and external doors

2.10 Windows or external doors providing emergency escape should comply with all of the following: 

  • Windows should have an unobstructed openable area that complies with all of the following.
    • A minimum area of 0.33m2.
    • A minimum height of 450mm and a minimum width of 450mm (the route through the
    • window may be at an angle rather than straight through). 
    • The bottom of the openable area is a maximum of 1100mm above the floor.
  • People escaping should be able to reach a place free from danger from fire. Courtyards or inaccessible back gardens should comply with Diagram 2.5.
  • Locks (with or without removable keys) and opening stays (with child-resistant release catches) may be fitted to escape windows.
  • Windows should be capable of remaining open without being held.

Work on existing dwellinghouses

Replacement windows

2.18 Work should comply with Parts K and L of Schedule 1 to the Building Regulations. When complete, the building should comply with other applicable parts of Schedule 1 to at least the same level as before.

2.19 Where an existing window would be an escape window in a new dwellinghouse, and is big enough to be used for escape purposes, then the replacement should comply with one of the following.

  1. The replacement window should be sized to provide at least the same potential for escape.
  2. If the existing window was larger than required for escape purposes, the opening can be reduced to the minimum described in paragraph 2.10.

2.20 If windows are replaced, it may be necessary to provide cavity barriers around the opening in accordance with Section 5.


  1. In this blog post we only mentioned the paragraph relating to architectural glazing. When specifying the requirements stated in Approved Document B and compliance of your project with Building Regulation Part B in terms of fire safety, it is important to consider the Approved document B as a whole.

Key Terms

Dwelling: Includes a dwellinghouse and a flat,

NOTE: A dwelling is a unit where one or more people live (whether or not as a sole or primary residence) in either of the following situations.

  • A single person or people living together as a family.
  • A maximum of six people living together as a single household, including providing care for residents.

Dwellinghouse: Does not include a flat or a building containing a flat. 

Escape route The route along which people can escape from any point in a building to a final exit. 

Final exit: The end of an escape route from a building that gives direct access to a street, passageway, walkway or open space, and is sited to ensure that people rapidly disperse away from the building so that they are no longer in danger from fire and/or smoke. (NOTE: Windows are not acceptable as final exits.)

Flat: A flat is a separate and self-contained premise constructed or adapted for residential purposes and forming part of a building from some other part of which it is divided horizontally.

Habitable room: A room used, or intended to be used, for people to live in (including, for the purposes of Approved Document B Volumes 1 and 2, a kitchen, but not a bathroom).

Means of escape: Structural means that provide one or more safe routes for people to go, during a fire, from any point in the building to a place of safety.


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