A smoke and heat exhaust ventilation system (SHEVS) keeps a smoke-free layer above floor level during a fire, so that people can escape and firefighters can see. In industrial buildings it is normally achieved with natural roof vents opening automatically on detection, sized to EN 12101-2 and combined with inlet air openings at low level.
The same roof units usually serve a second, everyday purpose: natural daylight and summer ventilation. This page covers how systems are sized, what the aerodynamic free area actually means, and what differs between European and Gulf regulatory practice.
What Smoke Ventilation Is For
Smoke, not flame, is what kills people and stops firefighting. A SHEV system exhausts hot smoke through the roof while fresh air enters at low level, maintaining a smoke-free layer between the descending smoke and the floor. The objective is a defined clear height for a defined time — long enough for evacuation and fire service intervention.
In a large single-storey industrial building this is almost always done naturally, using buoyancy. Hot smoke rises; if the roof is opened above the fire and air can enter below, a stable flow establishes itself with no fans and no power supply. That independence from electricity is precisely why natural systems are preferred in life-safety applications.
The system is more than the vents. It comprises roof units, smoke curtains or screens dividing the roof into reservoirs, low-level inlet openings, detection, and a control panel with battery backup that must operate when mains power has failed. A specification listing only vents is an incomplete system.
Geometric Area vs. Aerodynamic Free Area
The number that matters is Aa, the aerodynamic free area — not the physical opening size. A vent's geometric opening is reduced by its own frame, flap geometry and airflow losses, so a unit with 2.0 m² of geometric area may deliver only around 1.2 m² of aerodynamic area. Sizing against geometric area systematically undersizes the system.
Aerodynamic free area is determined by test under EN 12101-2 and declared by the manufacturer. Two vents of identical physical size from different manufacturers can have materially different Aa values, which is exactly why the standard requires the tested figure to be declared rather than calculated.
A tender that asks for "x m² of smoke vents" without stating whether that is geometric or aerodynamic area invites non-comparable bids. The compliant supplier quoting Aa looks expensive next to one quoting geometric area for the same money. Always specify Aa, and require the EN 12101-2 declaration of performance with the offer.
Natural or Powered Extraction?
Natural systems are preferred wherever the building geometry allows: no power dependency, no moving machinery to maintain, lower running cost. Powered smoke extraction becomes necessary in basements, enclosed car parks, atria and buildings without adequate roof access — anywhere buoyancy alone cannot establish reliable flow.
| Criterion | Natural (roof vents) | Powered (fans) |
|---|---|---|
| Power dependency | None for extraction | Required — with backup supply |
| Suitable buildings | Single-storey halls, warehouses, factories | Basements, car parks, atria, deep plans |
| Everyday secondary use | Daylight and summer ventilation | None |
| Maintenance | Actuator and control checks | Fan, motor and duct maintenance |
| Running cost | Negligible | Significant if used for daily ventilation |
The Second Job: Daylight and Summer Ventilation
Roof units specified for smoke ventilation can also serve as daylight rooflights and summer ventilators, opening on temperature to release accumulated heat at ridge level. This double duty is what makes the investment attractive outside the fire case, particularly in halls that overheat in summer.
Combined with an evaporative cooling system this becomes a coherent strategy rather than two unrelated purchases: cool fresh air is introduced at low level, hot air leaves through ridge vents, and the same openings are part of the life-safety system. Exhaust area sized for smoke is usually generous for ventilation purposes as well.
We supply Roda and Lamilux smoke vents and rooflights and GAL natural ventilation systems, with control panels, detection interfaces and battery-backed actuators.
European and Gulf Regulatory Practice
Across the Balkans and Türkiye, SHEV design follows the European route: products CE marked under CPR 305/2011 and tested to EN 12101-2, with sizing to national codes or DIN 18232. In the Gulf, authorities more commonly reference NFPA 204 and civil defence approvals, which use different calculation conventions.
Practically, this means the equipment is often the same but the design submission is not. We supply CE-marked, EN 12101-2 tested products with full declarations of performance; where a project is subject to civil defence approval under an NFPA-based code, the local consultant's calculation governs and we supply to that specification. Tell us which regime applies at enquiry stage and we will format the documentation accordingly.
Send us the building and the applicable code
Roof plan, building height, compartment areas and the regulatory regime. We return a vent schedule with declared aerodynamic free areas.
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Frequently Asked Questions
What is the difference between geometric and aerodynamic free area?
Geometric area is the physical size of the opening; aerodynamic free area (Aa) is the effective area after frame, flap geometry and airflow losses, determined by test under EN 12101-2. A vent with 2.0 m² geometric area may deliver only around 1.2 m² aerodynamic. Systems must be sized on Aa.
How much smoke vent area does a building need?
It depends on building height, compartment size, design fire and the clear layer height required by the applicable code — there is no single percentage. As a rough order of magnitude, natural SHEV area commonly falls between 2% and 5% of floor area, but that figure is for budgeting only and never for design.
Do smoke vents need a power supply?
The vents themselves do not require power to exhaust smoke — natural systems work by buoyancy. Power is needed for detection, the control panel and the actuators that open the vents, and that supply must be battery backed so the system operates when mains power has failed.
Can smoke vents also be used for daily ventilation and daylight?
Yes, and this is usually the main commercial argument for them. The same roof units serve as rooflights and as temperature-triggered summer ventilators, releasing accumulated heat at ridge level. The fire function remains independent and takes priority when detection triggers.
What standards apply?
In Europe, Türkiye and the Balkans: EN 12101-2 for natural SHEV products, CE marking under CPR 305/2011, with sizing to national codes or DIN 18232. In much of the Gulf, authorities reference NFPA 204 with civil defence approval. The equipment is often the same; the design submission differs.
Do smoke curtains have to be installed as well?
In larger roofs, yes. Smoke curtains or screens divide the roof space into reservoirs so that smoke collects above the fire rather than spreading thinly across the whole ceiling. Without reservoirs the smoke layer cools, loses buoyancy and descends — the vents then extract far less than the calculation assumed.
What maintenance does a natural SHEV system need?
Periodic functional testing of detection, control panel, battery condition and actuator operation, plus physical inspection of flaps, seals and drainage. Frequency is set by national code; annual testing with more frequent panel checks is common practice.
Do you supply outside Türkiye?
Yes. We supply Roda and Lamilux smoke vents and rooflights and GAL natural ventilation across the Balkans, the Levant, North Africa and the Gulf, with EN 12101-2 declarations of performance. Where a project is approved under an NFPA-based code we supply to the local consultant\u2019s calculation.