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Natural

Systems

Overview System Comparison Tech Specs Standards FAQ

Natural smoke ventilation systems

Harness natural airflow to clear escape routes safely

Natural systems use the natural buoyancy of smoke to extract heat and smoke through roof and façade vents, keeping stairwells and corridors clear for evacuation and firefighter access.

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How natural systems work

Stage 1

A signal is received from the fire alarm system.

Stage 2

Vents at the fire floor and at the head of the stair open to release smoke; all other vents remain closed.

Stage 3

Hot smoke rises and is drawn out through the roof, keeping the escape route clear.

Note: System configuration varies depending on building layout and shaft design.

Sertus products used in natural systems

Roof Single Leaf (RSL)

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Roof Single Leaf - Residential (RSL-R)

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Roof Louvre Blade - Residential Glass (RLB-RG)

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Roof Louvre Blade - Residential (RLB-R)

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Shaft Louvre Damper (SLD)

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Façade Louvre Blade – Residential Glass (FLB-RG)

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Façade Louvre Blade – Residential (FLB-R)

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Where natural systems work best

Natural smoke ventilation is ideal for simpler building layouts where smoke can rise freely and escape without powered assistance.

Low-rise buildings

Best suited to buildings up to 18m due to the risk of smoke logging in taller shafts.

No extended corridors

Works in code-compliant buildings without long travel distances that restrict smoke movement.

Space for a shaft

Requires a 1.5m² shaft that cannot be shared with other services.

Natural or Mechanical – which is right for your project?

Every building is different. This quick guide helps you understand whether a natural system will be suitable – before diving into the detail with our experts.

Technical information

Shaft Size

1.5m2 shaft throughout building, no smaller than 1.0m2 at any internal point.

Head of Stair Vent Size

1.0m2 free area required to provide inlet air. Circa 0.7m2 Aerodynamic Free Area.

Shaft Vent Size

1.0m2 free area shaft vent on every level. Circa 0.7m2 Aerodynamic Free Area. Fire doors cannot be used as vents.

Maximum Corridor Length

Can't be greater than 7.5m or 30m (one and two routes of escape respectively). Changes when sprinklered.

Core legislation

Approved Document B, 2019 edition volumes 1 and 2, plus May 2020 amendments.

Shaft Width

The shaft must have a minimum dimension of 0.85m in any direction.

Shaft Height

The shaft must extend a minimum of 2.5m above the ceiling of the highest storey served by the shaft and must be 0.5m above any surrounding structures within 2m of it horizontally.

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Guidance & Legislation

A high-level overview of the key standards that apply to natural smoke ventilation systems.

Approved Document B

BS EN 12101-2 (Natural Smoke & Heat Exhaust Ventilators)

Smoke ventilation regulations can be complex. We make them simple.

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Frequently asked questions

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Here are the questions we get most often about natural systems.

Can I use site-installed actuators on facade ventilation?

To be compliant all facade AOVs must be tested and certified to EN 12101-2. Site installed actuators are not certified to BS EN 12101-2 and therefore should not be used.

What’s the maximum height for facade ventilation?

Facade ventilation can't be used for fire-fighting shafts over 30m high. (Fire-fighting shafts must be provided in buildings more than 18m high.)

What's the longest corridor length for a natural system?

In natural systems, corridors can't be greater than 7.5m (one route of escape) or 30m (two routes of escape). When the apartments are sprinklered, this changes to 15m (one route of escape) and 60m (two routes of escape).

How big does a natural shaft have to be?

A natural shaft must have a minimum cross-sectional area of 1.5m2 (minimum dimension 0.85m in any direction). Further information regarding this can be found on Approved Document B Volume 1 (2019) 3.51.a.i

Your Natural Smoke Vents are tested to BS EN 12101-2:2003 why not BS EN 12101-2:2017?

BS EN 12101-2:2003 is the standard that our Roof Single Leaf - Residential (RSL-R) is tested to. This is the correct standard that it should be tested to. There is a 2017 version of BS EN 12101-2 however, this is not cited in OJEU (Official Journal of the European Union) and this essentially means that it is not in legislation and therefore it cannot be tested against.

Can I use standard riser doors in the shaft?

To be used as a shaft AOV the vent must be tested and certified to BS EN 12101-2. Generally, standard riser doors are not tested to this standard and therefore they should not be used in a natural ventilation system.