How many turbo ventilators does a roof need?

It follows from the volume of the building, the air changes required for the activity inside, and the throat diameter of the units chosen. A common industrial starting point is one 600mm unit per 80 to 100 square metres of roof, adjusted for heat load and ceiling height, but a shed with heat-producing processes needs many more than a cold store. Scattering a standard number across a roof without calculating air changes is guesswork.

Do they work when there is no wind?

Partly. They are driven by wind, but they also work on stack effect — hot air rising inside the building turns the turbine and escapes. On a still, hot day performance drops considerably compared to a breezy one. Where a guaranteed extraction rate is required, for a process or for smoke management, powered extraction is the correct answer and turbo ventilators are not a substitute.

Why do turbo ventilators leak?

Almost always at the base flashing, not through the unit. The base must be flashed into the roof profile with the correct upstand and the flashing dressed over the ribs, so water is shed around it. A base sealed with mastic onto the sheet is the usual failure, and it leaks within a season or two as the mastic ages and the roof moves thermally.

Turbo Ventilator Industrial Roof

What it is

A wind-driven rotating turbine mounted on a roof, extracting warm stale air from the space below without electrical power.

Specification at a glance

Property	Typical specification
Throat diameter	300mm, 450mm, 600mm common
Material	Aluminium, or stainless for corrosive air
Bearings	Sealed, maintenance-free, quality critical
Base	Profiled to match the roof sheet
Flashing	Upstand and dressed flashing, not mastic
Damper	Optional, for cold or dusty conditions

How they earn their place

No running cost and no power supply, which suits large sheds where extraction is desirable but ducted powered systems would be expensive to run.

Continuous background extraction, removing accumulated heat that otherwise builds under the roof through the day.

Simple, with nothing to fail except the bearings.

Where they are not sufficient

Requirement	Use instead
Guaranteed extraction rate	Powered extraction fans
Smoke management / fire strategy	Designed smoke vents
Process fume or dust extraction	Ducted extraction at source
Conditioned space	Sealed envelope, mechanical ventilation

Where projects go wrong

Base sealed with mastic instead of properly flashed. It leaks.
Quantity guessed rather than calculated from required air changes.
Cheap bearings that seize within a couple of years, after which the unit is just a hole in the roof.
Used in a fire strategy where designed smoke vents are required.
No damper in dusty locations, so dust and driven rain enter when the turbine is still.

Standards referenced

Ventilation provisions under NBC 2016, Part 8. Wind loading on roof-mounted items under IS 875 (Part 3). Envelope and ventilation requirements under ECBC 2017.

Turbo Ventilators — Wind Driven Roof Extraction

What it is

Specification at a glance

How they earn their place

Where they are not sufficient

Where projects go wrong

Standards referenced

Standards referenced

Frequently asked

Related