# Industrial Shed Ventilation: Turbo, Ridge or Powered Extract?

> Industrial shed ventilation removes the heat that builds under a metal roof by letting hot air out high up and drawing cooler air in low down. Turbo and ridge ventilators rely on wind and the stack effect; powered extract fans give a controlled rate; evaporative cooling lowers supply air temperature in dry weather. Inlets matter as much as outlets, and every roof opening is a leak risk.

## A hot shed is often an inlet problem

When a factory or warehouse shed is uncomfortably hot, the usual response is to
add roof ventilators. A dozen turbines go up, they spin, and the shed is not much
cooler. More are added the next year.

The misconception is that ventilation happens at the roof. **Air can only leave
the roof at the rate it can enter lower down.** A shed with large roof
ventilators and closed walls is like a chimney with the bottom blocked: the
outlets exist, but there is no flow through them. The low-level inlets, wall
louvres, openings and doors, matter as much as the outlets, and they are the
part most often missed.

For a plant head, heat under a metal roof is not only a comfort issue. It slows
people down, raises absenteeism through the hottest months, affects heat-sensitive
materials and equipment, and is one of the first complaints in a new building.
Getting the ventilation strategy right at design is far cheaper than adding
equipment in stages afterwards.

## How air moves through a shed

Two forces drive natural ventilation.

**Stack effect.** Warm air is lighter than cool air, so it rises and collects
under the roof. If it can escape high up, cooler air is drawn in low down to
replace it. The driving force increases with the height between inlet and outlet
and with the temperature difference between inside and outside. A tall shed with
a hot process ventilates more readily by stack effect than a low shed on a mild
day.

**Wind.** Wind passing over a roof creates suction at the ridge and leeward
side, which helps draw air out, and pressure on the windward wall, which pushes
air in. Wind is variable, so a design that depends only on wind performs poorly
on still days, which are often the hottest.

Both forces need a complete path: **in low, across the occupied zone, and out
high.** Inlets placed high, or outlets close to inlets, let air short-circuit
without passing through the space where people work. **IS 3103**, the Indian
code of practice for industrial ventilation, covers general and dilution
ventilation and measures to reduce heat hazards in industrial buildings, and
natural ventilation provisions also sit in **NBC 2016, Part 8**.

In practice, inlets are lost for ordinary reasons. Shutters stay closed for
security or to keep out dust, wall louvres are left off the cladding drawing to
save cost, and racking or stored goods are stacked against the openings that
exist. A design that relies on doors being open will not perform at night or
in the monsoon. Fixed low-level louvres with security mesh and weather blades,
sized with the outlets rather than added afterwards, keep the path open whatever
the doors are doing. The ventilation engineer sizes inlet and outlet areas
together, because one without the other sets the limit.

## Turbo, ridge, powered extract and evaporative cooling compared

| | Turbo ventilator | Ridge ventilator | Powered roof extract | Evaporative cooling |
| --- | --- | --- | --- | --- |
| How it works | Wind-driven turbine, assisted by stack effect | Continuous opening along the ridge with weather baffles | Electric fans exhaust air through the roof | Air drawn through wetted media, cooled by evaporation |
| Power | None | None | Yes | Fans and pumps |
| Rate | Varies with wind and temperature | Varies with wind and temperature | Controlled, set by the design | Controlled supply, needs matching exhaust |
| On a still, hot day | Reduced; stack effect only | Reduced; stack effect only | Unaffected | Unaffected, but less effective in humid weather |
| Rain and dust | Can admit both when still unless dampered | Baffles shed rain if well detailed | Shutters close when off | Media filters some dust; adds moisture |
| Maintenance | Bearings, base flashing | Low; inspect baffles and flashings | Motors, belts, shutters | Media, pumps, water treatment, cleaning |
| Where it suits | Background extraction over large roofs | Long sheds with a continuous ridge | Process heat, fumes, low sheds | Dry-season cooling of occupied zones |

None of these replaces roof insulation. Much of the heat in a shed arrives
through the roof itself; ventilation removes it after it has entered, while
[PEB insulation and thermal performance](/services/peb/peb-insulation-and-thermal-performance)
covers reducing the heat that gets in.

## Where each option fits

**Turbo ventilators** add continuous, free background extraction and are easy to
add to an existing roof. Their limitations are covered in detail on the
[turbo ventilator](/materials/turbo-ventilator) page: performance drops when the
air is still, and poor bearings turn a unit into a hole in the roof.

**Ridge ventilators** open the highest line of the roof, where the hottest air
gathers, with no moving parts. They have to be designed into the ridge and the
roof structure from the start, and their baffles must be detailed for wind-driven
rain.

**Powered extract** is the answer when the ventilation rate must be dependable:
heavy process heat, fumes or dust that must be diluted, or a shed too low for
stack effect to do much. The required rate is calculated by the ventilation
engineer from the heat and contaminant loads, not from a count of fans per bay.
Fumes and dust from specific machines are better captured at source with local
exhaust than diluted by roof fans.

**Evaporative cooling** lowers supply air temperature by evaporating water. It is
effective in dry heat and loses effect in humid monsoon conditions, when it adds
moisture to air that already has plenty. It needs a matched exhaust path, a
reliable water supply and a cleaning and water treatment regime, and it does not
belong near goods or processes that moisture would harm.

Many sheds use a combination: natural ventilation for background extraction,
powered fans in hot process zones, and evaporative units for occupied areas in
dry months.

## Dust, rain and the roof

Every ventilator is an opening, and openings let in more than air. Turbines that
stop turning can admit dust and driven rain unless they have dampers; ridge
ventilators rely on baffles; powered fans need shutters that close when they
stop. Bird mesh is often needed, and any filter or mesh reduces flow, which the
design should allow for.

The roof penetration is the more common problem. Ventilator bases are frequent
leak points when they are sealed with mastic instead of properly flashed into the
sheet profile, which is covered in
[warehouse roof leaks at skylights and sheet laps](/blog/warehouse-roof-leaks-skylights-and-sheet-laps).
Roof-mounted units also take wind load, and their fixing to the roof structure
should be checked by the engineer against **IS 875 (Part 3)**.

Finally, general ventilators are not smoke vents. Whether a building needs smoke
ventilation, and how it is provided, is part of the fire strategy decided by the
fire consultant and the authority under **NBC 2016, Part 4**.

## Common mistakes

- **Adding roof ventilators to a shed closed at low level**, so air has no way in.
- **Counting ventilators per bay** instead of designing a ventilation rate.
- **Relying on wind alone** for a shed with heavy process heat.
- **Ignoring roof insulation**, then trying to ventilate out the heat the roof
  lets in.
- **Using evaporative cooling through the monsoon** or beside moisture-sensitive
  stock.
- **Mastic-sealed ventilator bases** that leak within a season or two.
- **Treating ventilators as smoke vents** without a fire strategy.

## What to ask your designer and contractor

- Where does the air come in, and is the inlet area matched to the outlets?
- What heat and contaminant loads was the ventilation designed for?
- Which areas need a dependable rate, and are they on powered extract?
- How is rain and dust kept out when ventilators are still or fans are off?
- How are ventilator bases flashed into the roof sheet?
- Is smoke ventilation part of the fire strategy, and who has decided it?

## Standards referenced

Industrial ventilation, including general and dilution ventilation and heat
control, in **IS 3103**; lighting and natural ventilation in **NBC 2016, Part 8**;
wind loads on roof-mounted items in **IS 875 (Part 3)**; fire and life safety,
including smoke ventilation, in **NBC 2016, Part 4**. Ventilation rates, inlet
and outlet areas, equipment selection and fire strategy for a specific building
must be established by the project's ventilation engineer and fire consultant;
nothing on this page replaces that design.

## Frequently asked questions

### Is a turbo ventilator or a ridge ventilator better for a factory shed?

Neither is better in general. Turbo ventilators are discrete units spread across the roof, simple and cheap to add, with moving parts that need sound bearings. A continuous ridge ventilator opens the highest line of the roof, where the hottest air collects, with no moving parts, but has to be designed into the ridge detail. Both depend on wind and stack effect, and both need low-level inlets to work.

### Why is my shed still hot after adding more roof ventilators?

Usually because air cannot get in. Extraction at the roof only works if an equal volume of air can enter lower down, through wall louvres, openings or doors. If the shed is closed at low level, extra roof ventilators mostly draw air through each other or barely move at all. Roof heat gain is also a separate problem that insulation and roof colour address, not ventilation.

### When do we need powered roof extract fans?

When the ventilation rate has to be dependable regardless of weather, for example where processes release a lot of heat, where fumes or dust need diluting, or where the stack effect is weak because the shed is low. Powered fans give a controlled rate at the cost of power, noise and maintenance. The required rate is calculated by the ventilation engineer from the heat and contaminant loads.

### Does evaporative cooling work in a factory?

It is most effective when outdoor air is dry, because it cools air by evaporating water into it. In humid weather the cooling effect falls and the added moisture can make conditions feel worse, and it is unsuitable near moisture-sensitive goods or processes. It also needs a route for the air to leave, a reliable water supply and a cleaning and water treatment regime.

### Can roof ventilators be used as smoke vents?

Not by assumption. Smoke ventilation is part of the fire strategy, and its vents are designed and sized for that purpose, often with automatic opening. General ventilators are not designed to do that job. Whether smoke ventilation is needed, and in what form, is decided by the fire consultant and the authority under NBC 2016 Part 4.

### Do roof ventilators cause leaks?

Every opening in a metal roof is a potential leak point, and ventilators are a frequent one. Leaks usually come from the base flashing rather than the unit, especially where a base has been sealed with mastic instead of flashed into the sheet profile. A purpose-made base matched to the sheet, with the flashing lapped under the sheet above, is the reliable detail.

## Sources

- [IS 3103](https://standards.bis.gov.in/website/published-standards/department-wise) — Code of practice for industrial ventilation
- [NBC 2016, Part 8](https://www.bis.gov.in/standards/national-building-code/) — Building services - lighting and natural ventilation
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings and structures
- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/) — Fire and life safety

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Source: https://hagerstone.com/blog/industrial-shed-ventilation-turbo-ridge-or-powered