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A quick overview guide to The London Building Act (Amendment) Act: 1939 Section 20

Saturday, June 13th, 2009


Section 20 of the London Buildings Acts (and subsequent amendments) is concerned with the danger arising from fire within certain classes of building which by reason of height, cubic extent and/or use necessitate special consideration. The principles incorporated the provision of fire-fighting facilities that would enable the fire brigade to tackle the fire with utmost speed, but also provide warning of fire, contain an outbreak of fire and to prevent its spread.

This is quick guide to section 20 building requirements. But remember, always seek professional guidance.

Especially in relation to escape routes, building services, sprinkler or other automatic fire extinguishing,  or suppressant system, including hose reels; smoke extraction / venting system,  and vertical transport (including fireman’s lifts).

The London Building Act (Amendment) Act: 1939 Section 20
(Buildings of excess height and / or additional cubic extent)
(As amended 1985 & 2005)

Do the proposed works attract an application under this Legislation?

Application will be required if the building is:

  • More than 30 metres in height;
  • More than 25 metres in height with an area of any floor more than 930m 2.
  • A building of the warehouse class, or is a building or part of a building used for the purpose of trade or manufacture exceeding 7100m3 (250,000ft3) in cubical extent  unless it is divided  by division walls (with 4hr FR) such that no part of the building exceeds 7100m3 (see note 1).


If the proposed works bring the building into one or more of the above listed categories the building will then become subject to the above legislation requiring an application.


An Application is necessary if the works affect any of the following:

  • Sprinkler or other automatic fire extinguishing or suppressant system, including hose reels;
  • Smoke extraction / venting system;
  • A change to the access to the site for the Fire & Rescue Service;
  • Work that affects or impacts on any special fire risk areas (see Note: 2).

Where Approved Inspectors propose works within a building subject to LBA Section 20 it is mandatory that this local Legislation is recognised in the Initial Notice; failure to do so will result in rejection of the Initial Notice. Please note that this is irrespective of whether the proposed works impact on the criteria listed above or not. If the Council decides that a Section 20 Application is necessary then the Council will ask for this but will not delay validating the Initial Notice, providing that this local Legislation is expressly referred to in the Initial Notice, and confirmation is given that if necessary an application will be submitted in due course.

1)A building of the warehouse class means a warehouse, manufacturing, brewery, distillery with a cubic extent exceeding 4,247m3 (150,000ft 3) which is neither a public nor a domestic building. Please note for the purposes of this legislation the definition of a domestic building includes office use.
Height is taken from street level at the centre of the face of the building to the ceiling level of the top storey. Where more than half the roof is covered by a plant room such room becomes the top storey.

Cubic extent in relation to the measurement of a building means the space contained within the external surfaces and roof and the upper surface of the floor of its lowest storey but including any space within any enclosure on the roof of the building used exclusively for accommodating a water tank of lift gear or any like apparatus.

2.  Special Fire risk Areas:

  • Heat producing appliance above 220 kilowatts (heat);
  • Internal combustion engine producing above 44 kilowatts (power);
  • Oil-filled transformer or switchgear over 250 litres of oil and voltage above 1000 volts;

Flammable or combustible solids, liquids or gas manufactured, treated, handled or stored in quantities likely to constitute a fire hazard including any of the following:
i.    Fuel oil, diesel or petroleum;
ii.    Nitrate film or celluloid;
iii.   Cellulose or flammable liquid spraying