Installing effective roof ventilation in Australia is recommended as a top priority. It’s also a requirement of the Australian Building Codes applied to Australian Standards.
When selecting roof ventilation kits at your plumbing supplier you need to know which type of roof vent a property needs in a specific state territory.
Temperature extremes of the Australian climate cause an intense build up of heat within buildings during the summer months.
If you have inadequate roof ventilation your property will invariably suffer from mould and condensation, leading to timber rot. All costly building damage that can occur in the winter months too.
The entire structural integrity of your roof could be at real risk.
In this article …
You’ll find out the answers to those all-important questions you need to ask when looking for high performing, properly managed roof ventilation, including,
- What happens if a roof isn’t vented properly?
- Types of roof vents, such as whirlybird roof vents and bushfire roof vents
- Difference between Power roof vents and Static roof vents
- Why newbuilds may need better roof ventilation
- Roof ventilation according to NCC and Australia Building Code
First up, finding out why fast and super efficient roof ventilation is essential.
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What is the problem with roof ventilation?
In Australia, if a roof isn’t vented properly, then your property really is at risk of a problem.
There are 3 big risks:
- Risk No.1 Extreme temperatures
Lack of ventilation – or inadequate venting means as heat rises in your house it has no natural means of escape. The heat will simply be absorbed by the roof.
In the summer – temperatures can hit 41˚C and above. The rising heat absorbed in the roof simply builds up. At the same time, the benefit of using an air conditioning unit is also lost as the cooled air is also trapped in the roof space. A costly loss.
Like a pressure cooker, the build up of heat becomes intolerable, not least because of the hot air forming condensation in the roof spaces.
Australian states typically affected: South Australia, Western Australia, Northern Territory Queensland and New South Wales.
In the winter – more potentially damaging condensation forms because the roof space is colder.
Australian states typically affected: New South Wales, Tasmania and Victoria.
Unvented levels of heat build-up brings us to:
- Risk No.2 Condensation creating mould and wood rot
Condensation can enter the ceiling boards and rafters – as well as moisture dripping down onto the insulation below – and forming harmful mould and wood rot.
In some cases, the integrity of part of the roof structure can be seriously compromised, and will need a costly rebuild.
- Risk No.3 Inefficient, costly energy use
At any time of the year, but especially during extreme hot or cold weather, heavy use of air conditioning or air heaters is not only inefficient but can be expensive to run.
The solution is:
- Cool air flowing uniformly through the roof space from the outside, and
- Directing the hot and condensed air through a fitted exhaust vent
Let’s look at the types of roof vents usually available …
What ventilation is required for my roof?
Trade plumbing suppliers will often stock a range of roof ventilation kits, which may look very similar. The first thing you need to know is:
Difference between Power roof vents and Static roof vents
- Power roof vents – considered a more effective vent for hotter locations, this circular low profile vent uses an electric / motorised fan system to actively direct air flow in and out of a building. Power roof vents are usually connected directly to the building’s electrical wiring system.
- Static roof vents – also known as a passive system – this type of vent simply circulates the natural movement of air through a building without the use of an electric fan / turbine system.
Examples of Static roof vents
Whirlybird Roof Vents – a dome-shaped ‘turbine’ vent that’s probably one of the most recognised type of roof vent.
It’s precisely contoured fins rapidly rotate to create a vacuum and draw heated air up through the roof.
Roof temperature can reduce by up to 30 per cent. (Commonwealth Scientific and Industrial Research Organisation – CSIRO), 2018).
Box Vents – also known as louvre vents, can be both square-shaped and round. This vent type is covered and normally installed near the ridge or “peak” of a roof.
Gable vents – similar to box vents but are installed in triangular areas on the gable ends of a building.
Solar-powered Bush fire rated roof ventilators – operate independently of the electricity grid.
Bushfire-rated vents – box shaped units which simply allows hot air to escape from the roof.
Solar vents – also called solar attic fans, use a small solar panel to power a fan or exhaust unit.
Bushfire-rated ventilators – are wind-driven turbine units which actively:
- Expel hot air from the roof
- Restrict embers from entering and
- Help to evacuate smoke.
Why newbuilds may need better roof ventilation
Many of today’s newbuild homes are considerably more airtight than previous constructions. Today, a popular design trend is to have a low profile, sloping flat-plane roof.
Which means there is a reduced roof cavity alongside increased insulation.
As a result, air circulation is also reduced leading to problems of trapped moisture, and the risk of mould and timber rot.
An inadequate roof ventilation system – combined with extensive insulation throughout – may need a vent upgrade to allow trapped air and condensation to escape.
Roof ventilation according to NCC and Australia Building Code
Under the Building Code of Australia Volume 2, 2008 and National Code of Construction (NCC) Amendment 2-part 3.8.5, 2019:
3.8.5.2 Ventilation requirements
- A habitable room, WC, bathroom, shower room, laundry and any other room occupied by a person for any purpose … should be adequately ventilated to reduce or eliminate condensation and odour.
- An exhaust fan or other means of mechanical ventilation may be used.
It also means a roof must be assessed for adequate ventilation to allow air to be expelled via an exhaust fan.
Under the National Code of Construction (NCC) Amendment 2-part 3.8.7.4, 2019:
3.8.7.4 Ventilation of roof spaces
- An exhaust system directing air flow into a roof space must be ventilated to outdoor air through evenly distributed openings.
- 30 per cent of a total unobstructed ceiling – related to roof pitch – must be located not more than 900 mm below the ridge or highest point of the roof space. The remaining area to be provided by eave vents installed under the house eaves for circulating air in the roof space.
In a nutshell …
The intense build-up of heat within buildings during the summer months and the effect of the cold during the winter means:
If you have inadequate roof ventilation your property can be severely harmed by condensation, mould and eventually, timber rot.
New-build roof design can also be susceptible.
Under Australian Building and Construction codes your property must have an adequate roof ventilation system to enable the flow of air to the outside.
Power roof vents are more effective in hotter locations but there are a number of popular, high- performing static/ passive roof vents which can also be fitted as standard, including whirlybird roof vents, box vents, solar powered vents and bushfire rated vents and ventilators.
FAQs
Q: What is the best way to ventilate a roof?
A: Power roof vents that use an electric fan system to force air more quickly from the roof space are considered the most efficient type of roof ventilation.
Q: How many air vents do I need in my roof?
A: The number of roof vents will depend on area climate, size, pitch and roof type. Hotter climates may need more vents to allow hot air to escape. It’s recommended a roof with damp proofing should have one roof vent fitted for every 27.8 sq. m (300 sq. ft) or every 13.0 sq. m (150 sq. ft) without damp proofing.
Q: How high does a vent have to be through a roof?
A: High-level ventilation openings should be at the ridge or no more than 900 millimetres below the ridge or a roof’s highest point, according to the NCC.
