The LWF Blog
Fire Safety Engineering for Design – Sprinkler Installation Planning – Part 249
August 26, 2025 10:20 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 248, LWF discussed drencher systems for glazing, and looked at the suppression of fire in atriums. In part 249, we continue to talk about the protection of atriums from fire.
With all fires in an indoor space, the hot gases from the fire will collect first at the highest point of the roof. In the case of spaces with sloping soffits or roofs, this will be the height of the peak or ridge. Sprinklers should be located within a reasonable distance from the ridge when the roof slope is steeper than 1 in 3, or 18.5°.
The positioning of the sprinkler heads in relation to the ceiling or soffit is important and affects the speed at which the sprinklers become operational in a fire situation. The hot gas layer adjacent to the soffit will be partly cooled by the fabric of the ceiling and so sprinklers should be placed between 75 mm and 150 mm below any soffit so the sprinkler output will target the hottest gases.
In a space where suspended ceilings are employed, the void between the suspended ceiling and the floor above should be protected if it is greater than 0.8 m deep. It is common for building occupants to use such spaces for the storage of miscellaneous materials, such as files, Christmas decorations etc.
Where ceiling voids are less than 0.8 m deep, an assessment should be carried out to ascertain the level of risk, considering elements such as construction material flammability, fire loads expected in that area from HVAC parts, duct insulation, cables etc., and also, to consider the proximity of combustible items to potential ignition sources.
The pipework design for a sprinkler system has three principal styles. The first is ‘Tree’ or terminal systems. The second is ‘Gridded’ systems and the third is ‘Looped’ systems. Each will be discussed in some detail to ascertain the suitability of each style for the purpose intended.
In part 250 of LWF’s series on fire engineering we will continue to discuss sprinkler protection by looking at the three main styles of pipework for sprinkler system. 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.