The Australian sun is renowned for its power, and it doesn’t discriminate when it comes to your building’s roof. With daily blasts of heat, your roof cavity rapidly heats up, which becomes trapped and heats up the rest of your building. Conversely, on brisk winter nights, it’ll trap cold air and might make your building cooler than you’d like.
Does roof ventilation really work? Absolutely. Roof ventilation is an effective and efficient way to help regulate the temperature of your property, but only when done right. In this article, we’ll discuss how roof ventilation works, its benefits, and what needs to be done for it to work effectively.
How does roof ventilation work?
The goal of roof ventilation is to refresh the air in your roof cavity. In summer, this means letting cooler fresh air into the roof from outside, and pushing warmer air out. In winter, it’s letting warmer air in, and pushing colder air out.
Fresh air enters the roof cavity from vents, usually placed under the eave where the sun can’t reach it. It can also enter the roof via a ceiling grille inside the property itself, though this is optional. Stale air is extracted from the roof through a fan turbine vent such as a silver whirly bird, which can either be powered by electricity and running constantly, or spun by natural air pressure and wind flowing over the property. Whirly birds also double up as funfair rides for bored pigeons who feel like going for a spin.
Other types of outlet vents include box vents, which are unpowered boxes with air grilles, or ridge vents that sit along horizontal edges along the roof. Both of these vent types allow air to escape through natural convection.
What are the benefits of roof ventilation?
The main benefit of roof ventilation is to regulate the temperature of your roof cavity, so that it doesn’t heat or cool the rest of your property. If you’re living in a building with an unventilated roof, your air conditioning will be working harder to cool your property. Air conditioning consumes a lot of energy, so roof ventilation can help to improve the energy efficiency of your home, and keep your bank account healthy in the long-run.
Roof ventilation also prevents moist air from accumulating in your roof cavity, which can create extremely humid conditions, with water dripping from the rafters. If it’s raining in your roof, there’s a big problem! Wood and other construction materials absorb water, which eventually, can threaten the structural integrity of your home², in addition to producing swatches of smelly mould. Termites love damp conditions too, and it’s a big problem when those suckers get into your property.
Finally, roof insulation prevents warm air from flowing into the rest of your property, and by ensuring that your roof cavity is properly ventilated, your insulation will be protected from damaging levels of humidity.
Key considerations for roof ventilation
There’s no question that roof ventilation works, but for it to be effective, there’s some key things to consider.
1. Vent and fan locations
As sun-baked Australians, it’s safe to assume that we’re more interested in cooling our properties than heating them. For this reason, because warm air rises, our extraction fans are best placed in the highest areas of the roof, making it easier for them to pull up already-rising air and extract it from the roof cavity. As already mentioned, intake vents are best placed under the shadowy eave of the roof, where the air is slightly cooler.
2. Size of inlet and outlet vents
The size of your inlet and outlet vents will depend on the size of your roof cavity. Large roofs will need larger inlet and outlet vents, which can handle more volumetric flow. It’s recommended to aim for ten air changes per hour in your roof cavity¹.
Outlet vents/fans are more effective when they’re powered. These can be powered by solar energy, or connected to the property’s electricity. In fact, some solar-powered vents are believed to be twenty times more powerful than a standard whirly bird, making them an effective way to extract warm air from a roof cavity³.
3. Similarly-sized inlet and outlet vents
Given that ventilation circulates the air in your roof cavity, it’s important to have a similar amount of air going in and out. If you have a huge vent letting in large amounts of air, and only a single outlet vent extracting it, the air won’t circulate as quickly, affecting the temperature regulation. To install effective ventilation in your home, you’ll need to understand the airflow (volumetric flow) rate of your inlet and outlet vents, and match them as closely as possible to ensure a good balance.
Roof ventilation is an important part of climate control in your home. By refreshing the stale air in your roof, ventilation is an effective way to regulate its temperature and humidity, ensuring that the rest of your property stays nice and cool during Australia’s scorching summer months.