The LWF Blog
Fire Safety Engineering for Design – Sprinkler Installation Planning – Part 246
August 4, 2025 10:45 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 245, LWF discussed the potential impact of early consideration of the relevant premises on sprinkler installation design. In part 246, we discuss sprinkler installation design, including factors affecting design and the building’s construction features.
A building’s construction features, such as its height, layout, mechanical and electrical services, impact upon the spacing and location of sprinklers and the speed of response and effectiveness of the sprinkler protection provided. It is crucial that all elements of the building’s design are taken into account when planning a sprinkler installation.
Planning to avoid any potential obstructions is an issue of significance when working on sprinkler design plans and subsequent installation. It is necessary to co-ordinate with all aspects of the building design, infrastructure and services on site.
The underlying principles of sprinkler installation design are relatively logical and are based, largely, on common sense, but only with a thorough knowledge of fire dynamics.
BS EN 12845 gives sprinkler head spacing by risk, maximum values (area per sprinkler/m2) as follows:
Light hazard – 21
Ordinary hazard – 12
High hazard – 9
Whereas, NFPA 13 gives slightly different numbers for the same criteria:
Light hazard – 11.1 – 20.9
Ordinary hazard – 12.1
High hazard – 8.4 – 12.1
The numbers/ranges given should not be taken as a target, but rather the maximum values.
In a high hazard risk, it may be prudent to ensure the spacing of sprinklers is lowered to a value below the maximum to reduce the hydraulic demand on the system.
The spacing may be reduced in some areas to compensate for an increased risk. The design approach of a sprinkler system installation should be balanced and based on available knowledge and appropriate engineering skills and experience.
When a sprinkler system design is a part of an overall fire-engineered design for the building, the speed of sprinkler operation may be a crucial element of the strategy. The spacing and location of the sprinkler heads relative to the ceiling or roof must be considered carefully.
In part 247 of LWF’s series on fire engineering we will discuss the spacing of sprinklers, including maximum allowable distances between sprinkler heads. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.