BS9251 British Standard for Fire Sprinklers

BS9251:2021 The British Standard for Fire Sprinklers

BS9251 is the British Standard for Fire Sprinkler Systems in the UK. This is the 3rd version of this standard, originally published in 2005 then reviewed and amended in 2014  and 2021 with help from members of the fire service and key players in the industry. 

BS9251 covers:

  • Individual dwellings (houses, flats and maisonettes)
  • Houses of multiple occupancy (HMOs)
  • Bed and breakfast accommodation
  • Boarding houses
  • Blocks of flats
  • Residential care premises
  • Dormitories
  • Hostels

The standard does not cover schools, hospitals, hotels or commercial buildings. Any sprinkler systems for commercial properties are covered by BS12845:2021 The British Standard

The types of property covered by BS9251 vary in size and type of resident and therefore are split into risk categories. These categories range from 1-4.

Category 1 covers individual dwellings (houses), HMO’s, B&B’s, Boarding Houses (Typically a domestic dwelling (house) for a single family).

Category 2 covers blocks of flats below 18m (typically less than 6 floors), small residential care homes, sheltered and extra care housing.

Category 3 covers large residential care homes, student accommodation, dormitories, hostels.

Category 4 covers blocks of flats 18m and above. (Typically about 6 floors or more)

Also see more on our news blog

Each category has minimum design parameters which determine the number of heads that should be used to calculate the amount of water and pressure required to run the system. The total number of heads required in any system is dependent on the room sizes, use and area covered by an individual head. Typically, 1 head can cover 25m2 but should not be more than 2.75m from a wall and no closer than 2.4m from another sprinkler head.

  • Category 1 sprinkler systems will require a minimum run time of 10 minutes and the calculation should include 1 or 2 heads in the calculation. Average 84-100 litres/minute. Tank size 1m³ to 1.5m³.
  • Category 2 sprinkler systems require a minimum run time of 30 minutes and the calculation should include 1 or 2 heads in the calculation. Average 84-100 litres/minute. Tank size 3m³ to 4.5m³.
  • Category 3 sprinkler systems must have a minimum run time of 30 minutes and the calculation should include 2 or 4 heads in the calculation. Average 168-200 litres/minute. Tank size 6m³ to 9m³.
  • Category 4 sprinkler systems as per Category 3 but must have a minimum run time of 60 minutes. Two or more tanks, each capable of providing 50% or more of the required water supply to the system. Backup power supply.

Certain non-residential accommodation falls within the scope of the new BS9251:2021 including:

  • Car parking within / beneath flats / domestic garage
  • Bin Store, residents’ storage sheds
  • Plant rooms PTSN / CCTV / Electrical rooms
  • Laundry / utility room: domestic or institutional eg care home
  • Kitchens: domestic, self catering eg student accommodation, residential care
  • Foyer / reception / limited office areas (e.g. concierge or site management)

Sprinklers Direct will design and hydraulically calculate the system to find the required system demand and delivery method.

Further information: Fire Sprinkler Health & Safety | Fire Sprinkler Materials


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Case Study

Shared Boosted Riser in Lewisham

Client: Orchard Plumbing

Risk Category: Cat 2, 2 head risk, 30 minutes run time
Number of heads: 606
System Type: Shared Boosted Riser

This fire sprinkler installation in Lewisham related to 2 blocks of flats and maisonettes.


Shared Boosted Riser in Lewisham

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Very efficient from start to finish. We required Sprinkler design and installation on our office to residential conversion. Becky and Jordan handled this in a very professional and competitive way. Thanks again to the team.

Matthew J.


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