Natural Smoke Ventilation
This is covered quite extensively in Approved Document B (2006). It states as follows:
Smoke control of common escape routes by natural smoke ventilation:
In simple buildings, the corridor or lobby adjoining the stair should be provided with a vent. The vent from the corridor/lobby should be located as high as practicable and such that the top edge is at least as high as the top of the door to the stair. There should also be a vent, with a free area of at least 1.0m2, from the top storey of the stairway to the outside. In single stair buildings the smoke vents on the fire floor and at the head of the stair should be actuated by means of smoke detectors in the common access space providing access to the flats.
In buildings with more than one stair the smoke vents may be actuated manually (and accordingly smoke detection is not required for ventilation purposes). However, where manual actuation is used, the control system should be designed to ensure that the vent at the head of the stair will be opened either before, or at the same time, as the vent on the fire floor.
Vents should either:
- be located on an external wall with minimum free area of 1.5m²; or
- discharge into a vertical smoke shaft (closed at the base) meeting the following criteria:
- Minimum cross-sectional area 1.5m² (minimum dimension O.85m in any direction), opening at roof level at least O.5m above any surrounding structures within a horizontal distance of 2.Om. The shaft should extend at least 2.5m above the ceiling of the highest storey served by the shaft;
- The minimum free area of the vent from the corridor/lobby into the shaft and at the opening at the head of the shaft and at all internal locations within the shaft (e.g. safety grilles) should be at least 1.0m²
- The smoke shaft should be constructed from non-combustible material and all vents should have a fire/smoke resistance performance at least that of an E30Sa fire door. The shaft should be vertical from base to head, with no more than 4m at an inclined angle (maximum 30°); and
- On detection of smoke in the common corridor/lobby, the vent on the fire floor, the vent at the top of the smoke shaft and to the stairway should all open simultaneously. The vents from the corridors/lobbies on all other storeys should remain closed.
For additional and impartial advice or guidance on your smoke ventilation requirements please feel free to contact us about meeting the requirements of either the Approved Document B or Scottish Technical Handbook.
The above is only guidance, for assistance please contact us.