# Turbo Ventilators — Wind Driven Roof Extraction

> A turbo ventilator is a wind-driven rotating turbine mounted on a roof that extracts warm, stale air from the space below without electrical power, helped by hot air rising inside the building. It gives continuous background extraction with no running cost, but cannot guarantee an extraction rate, so it is no substitute for powered extraction or designed smoke vents.

## 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**.

## Frequently asked questions

### 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.

## Sources

- [NBC 2016, Part 8](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Building services — ventilation
- [IS 875 (Part 3)](https://standards.bis.gov.in/website/published-standards/department-wise) — Wind loads on buildings
- [ECBC 2017](https://beeindia.gov.in/) — Building envelope and ventilation

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Source: https://hagerstone.com/materials/turbo-ventilator