While few experts would question the importance of roof ventilation in a home, some debate does exist in terms of the effectiveness of different roof ventilation applications. There is also different schools of thought about the amount of ventilation that’s required – excessively ventilating a roof can be just as detrimental as having no roof ventilation at all. It can also leave your roof more vulnerable to leaks, bad weather conditions and foreign objects entering your home through the roof. But why is roof ventilation so important?
How roof ventilation is affected by temperature
Roof ventilation technologies are regularly recommended in warmer climates, mainly because without ventilation the temperature of a roof space becomes excessively hot which will penetrate the ceiling and begin to heat up the house. This makes it difficult to cool living spaces even with adequate air conditioning.
In Australia, roof spaces can heat up to 35 degrees, however the optimum roof space temperature is 28 to 30 degrees with a constant flow of air. This is regardless of whether the outside temperature is hot or cold, so it can be advantageous for the air in the roof to be constantly flowing.
However, the usefulness of roof ventilation in colder climates is debatable given that homeowners essentially need to retain heat in the roof rather than flush it out. According to some experts, some roof ventilation counteracts a home’s insulation which can create what’s called ‘wind washing’, where heat is taken from the ceiling by excessive air movement.
They maintain that ventilation shouldn’t be activated during the colder months, and other methods like good insulation and proper sealing adopted. However, this is only relevant if the roof space is dry. Roof spaces with high moisture levels need good ventilation all year round in order to prevent damage to the roof structure. Constantly flowing air can also enable the heat coming from internal heating systems to fill the space more quickly and efficiently.
Yes… it’s confusing! So to help you make an informed choice, let’s look at some of the basic types of roof ventilation.
Passive ventilation
One of the most economical methods of ventilating your roof, passive ventilation is the process of supplying air to and removing air from indoor spaces without using mechanical systems. The science behind it is based on making the most of the flow of external air to an indoor space as a result of pressure differences that arise from natural forces.
In the building phase, passive ventilation involves using natural sources of heating and cooling, like the sun and cooling breezes, and it can be achieved by appropriately orientating your home and carefully designing its building ‘envelope’ (which are the walls, windows, roof and floors of a home). Installing roof vents, solar chimneys, the use of evaporative cooling methods, and maximising a home’s earth-coupled thermal mass can also assist with passive ventilation. Ensuring roof spaces are well ventilated and the use of foil insulation and light coloured roofing can also limit radiant heat flowing into the roof space.
Roof vents
Installing roof vents are a great way of not only ventilating your roof, but they can minimise moisture in the roof cavity, prevent the build-up of warm air, and maintain an ideal balance between the environment inside and outside your home.
Roof vents come in a range of shapes and sizes with distinct features that make them ideal for certain situations, and include:
- Flat or box vents are static vents with no moving parts, and they allow air to escape through natural convection. They are typically constructed of plastic or metal and installed over an opening that’s cut into the roof.
- Ridge vents cover the entire length of a horizontal edge of your roof and can assist with the even distribution of temperature.
- Power vents employ the use of motors that operate fans to drive hot air out of your home. They need electricity to operate, so homeowners either hardwire these into their mains power or choose models that come with dedicated solar panels that power them.
Whirlybirds
One of the most common types of roof vents are whirlybirds, also known as turbine vents, which are cylindrical domes with fins that spin in the wind to create a vacuum while they suck up warm air into a roof cavity. ‘Active’ vents are mechanically driven, turn continuously and make a permanent vacuum regardless of the wind speed, while passive vents require wind to spin the turbine.
Whirly birds can range in capacity from 100-200 cubic metres per hour to around 2,500 cubic metres per hour in a commercial setting. Although they are fairly limited in terms of effectiveness on their own, they can play a role in a well-designed ventilation system.
Solar ventilation
Solar powered ventilation needs (not surprisingly) the sun in order to work efficiently, and it can have a significant impact on a home’s temperature. Roof fans or vents powered by solar energy are quiet, compact, environmentally friendly and have no operating costs. They can also improve air circulation in the roof cavity, and during winter months, they prevent moisture build-up and reduce mould, keeping the roof space dry and fresh.
In terms of solar ventilation in roofing, some products also include thermostat switches to control temperature or automatic shut-off capabilities that can help preserve beneficial roof space heat in the cooler months.
Need some advice on the most suitable roof ventilation for your home? Contact us on (07) 3623 4422 for a quote!