A whirlybird is a wind-driven roof ventilator. As wind spins the turbine head, it draws hot, moist air out of the roof space, and replacement air comes in through the eaves and gaps in the roof. It needs no power, has no running costs, and is one of the simplest ways to provide the high-level roof space ventilation that the building code now expects in Melbourne.
The short answer
- Wind spins the head and draws air out of the roof space
- They remove heat, dampness and condensation
- Air needs a way in, usually at the eaves
- Melbourne's climate zone has roof ventilation rules
- On tiled roofs, flash the base properly
How whirlybirds work
The curved vanes on a whirlybird catch the wind and spin the head. The spinning head creates low pressure in the throat, pulling air up out of the roof space. Even without wind, warm air rising through the throat keeps a gentle flow going. For the system to work, air must be able to enter the roof space low down, usually through eaves vents or gaps at the eaves, so it can sweep through and out the top.
Why ventilate a roof space
- Heat: on hot days roof spaces get far hotter than outside air, and that heat radiates down through the ceiling.
- Moisture: warm, moist air from showers, cooking and breathing rises into the roof space and can condense on cold surfaces such as sarking and roof timbers.
- Condensation damage: repeated condensation can stain ceilings, rot timbers and damage insulation.
The Ampelair Spinaway we stock is marketed to remove trapped hot air, dampness and condensation from roof spaces without using power.
What the code requires in Melbourne
Melbourne is in climate zone 6. The National Construction Code housing provisions (Part 10.8) require roof spaces in climate zones 6, 7 and 8 to be ventilated, unless the roof space sits directly under the tiles of an unsarked tiled roof, or above sarking with a vapour permeance of at least 1.14 µg/N.s. For pitched roofs of 15 degrees or more, the code sets ventilation openings of 7,000 mm² per metre at the eaves and 5,000 mm² per metre at high level, with high-level openings at the ridge or within 900 mm of it. The code also excludes some roof types, such as concrete roofs.
These rules apply to new work. A whirlybird near the ridge is one way to provide high-level ventilation; eaves vents provide the low-level openings.
How many do you need?
It depends on the size of the roof space, the roof shape and the ventilation area each unit provides. For new work, calculate the high-level ventilation area the code requires from the length of the roof and compare it to the free ventilation area on the product data sheet. For an existing home, roofers often fit one or two on a typical house and add more on larger or more complex roofs. Place them near the ridge, spread across the roof space rather than bunched together.
Fitting one to a tiled roof
Walking on tiles cracks them and puts you at risk of a fall. WorkSafe Victoria treats falls from roofs as a serious hazard and puts edge protection ahead of ladders and harnesses. If you are not trained and equipped to work at height, use this guide to buy the right products and brief a roofer.
- Choose the position near the ridge, between rafters, away from valleys.
- Remove tiles and cut the opening, keeping the rafters intact.
- Fit the base and adjust it so the head sits level.
- Flash the base into the tiles with a flexible flashing that dresses into the tile profile, such as Fast-a-Flex or Dakaflash. See our roof flashing guide.
- Cut and refit tiles around the base and fix them.
- Check the head spins freely and the flashing sheds water away from the opening.
What whirlybirds will not do
- They will not cool a home on their own. Ceiling insulation and shading do most of that work.
- They cannot move air that has no way in. Without eaves or low-level openings, they underperform.
- They do not fix leaks or condensation caused by blocked gutters, failed sarking or bathroom fans venting into the roof space.
We stock the Ampelair Spinaway 300mm in Mill, Monument, Manor Red, Pale Eucalypt and Woodland Grey to suit most roof colours. See roofing materials.
Blocked gutters are a common cause of roof space dampness. Our sister business PorterVac cleans gutters across Melbourne.
Common questions
Do whirlybirds actually work?
Yes, when the roof space has low-level openings for air to enter. Wind spins the head and draws hot, moist air out of the roof space.
Do whirlybirds let rain in?
A correctly fitted and flashed unit is designed to shed rain. Leaks usually come from poor flashing around the base.
How many whirlybirds does a house need?
It depends on the roof space and the ventilation area each unit provides. For new work, size it against the NCC ventilation requirements.
Do whirlybirds work without wind?
More slowly. Warm air rising through the throat keeps some air moving, but the main effect comes from wind spinning the head.
Is roof ventilation required in Melbourne?
For new work, the NCC requires roof space ventilation in climate zones 6 to 8, which include Melbourne, with some exceptions.
Related
Sources: NCC 2022 Housing Provisions Part 10.8: Condensation management; WorkSafe Victoria: Prevention of falls in housing construction.
