The LWF Blog
Fire Safety Engineering for Design – Natural Smoke Shafts – Part 207
October 28, 2024 11:30 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 206, LWF began to look at natural ventilation systems and the three types available. In part 207, we talk about natural smoke shafts and their use in residential buildings.
Natural smoke shafts are used most often to ventilate staircases and lobbies serving firefighting shafts or residential common corridors. Their main purpose lies in protecting the adjoining stairway by ventilating the lobby or corridor that provides access to the staircase. The natural ventilator from the lobby or corridor leads to a vertical smoke shaft which is naturally ventilated to the outside at the top of the shaft. Replacement air is also commonly provided naturally, through a vent at the head of the adjoining (protected) staircase.
A door is provided separating the staircase and the adjoining lobby or corridor, meaning that the system is only fully functional when the stair door is open.
The system works due to a net flow of air between stair and lobby, ensuring the staircase is kept clear of smoke. Tenability when the stair door is closed (and no inlet air is available) and when the stair door is open may have limited success, and so requires careful consideration and design.
Shaft design requirements are commonly prescriptive and so the designer should reference the appropriate local codes prior to designing smoke shaft systems.
Residential Buildings
In England and Wales, smoke shafts for residential buildings should have a minimum area of 1.5 m2, and a minimum dimension of 0.85 m in any direction. The shaft should terminate at 0.5 m above any surrounding structures (above roof level) and within a horizontal distance of 2.0 m.
The shaft should be designed to reach at least 2.5 m above the ceiling of the highest story served by the shaft. This restriction means that the top floor of a building should generally be vented in a different manner, as it is not always appropriate to vent the top floor level via the smoke shaft.
An adjoining staircase should be ventilated directly to the outside by a 1 m2 vent at top storey level, this should open at the same time as the lobby vent.
The Smoke Control Association provides guidance on smoke ventilation for residential buildings.
In part 208 of LWF’s series on fire engineering we will discuss natural smoke shafts for firefighting shafts and consideration of wind overpressures. 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.