Understanding Passive Ventilation

Understanding passive ventilation

A lack of ventilation creates a series of highly problematic building issues, the most significant being:

  • Condensation inside roofs and walls buildup resulting in damp bearers and joists - leads to rot and then makes the structure unsound
  • Mould issues - a health hazard and major problem in Australia’s climate
  • A build-up of carbon dioxide - can lead to headaches, lethargy and breathing difficulties
  • Lack of air exchange leading to temperature differentials - uncomfortable for occupants
  • Higher energy costs - people need to mitigate the above with electric or gas solutions.

Passive ventilation can assist to mitigate all of these issues.

Location, location, location

How proper roof ventilaltion works

In order for ventilation to be effective, there must be an adequate exchange between the air in the building and outdoors.

This can be impacted by the building’s location and the elements surrounding it. By factoring in exposure to sun, shade, and prevailing wind velocity and direction, you can then build in a way that will enhance the natural air-flow.

For those looking for information, the National Construction Code regulates thermal performance on a building and provides information on sheet roofing, tiles and shingles, as well as required energy efficiency and acceptable construction practices to achieve compliance (Part 3.12).

Quality membranes

Breathable membranes

Membranes are an important layer of protection in terms of weather-related damage, but they also prevent condensation and water ingress, improve energy efficiency, improve indoor air quality, and absorb UV radiation.

They are resistant to wind uplift so they also minimise draughts. Draughts are not the same as ventilation. Ventilation is purposeful airflow and an air-tight building must still have air circulation.

This is why breathable membranes are the ideal adjunct in a vented roof space.

Breathable membranes are permeable to water vapour, permitting air circulation through the wall and roof cavity, and preventing moisture built-up by allowing it, in vapour form, to cross the membrane fabric and make its way out, working through the entire roof undersurface and not just relying on the ventilation openings.

Trapped moisture from condensation is problematic but this issue can be alleviated with the adequate use of a breathable membrane.

Venting options


Buoyancy-driven ventilation

Buoyancy-driven ventilation, sometimes called “the stack effect”, allows cool air to come in at a lower level through the use of low vents while the hot air rises up and exits via a high ventilation solution.

Ceiling, roof and gable vents are placed higher in a structure and allow the accumulated hot air to rise and escape. Passive vents under eaves (“soffit vents”) allow for fresh air to enter the roof space.

Combining soffit vents with ridge vents – typically placed at the high ridge point of the roof – allows the air to circulate and provides an essential egress for the hot air.

Wind-driven whirlybirds are also a viable solution but they are more visible on the roof exterior.

Ridge ventilation systems

Ridge ventilation systems, such as Vent-a-Roof, are completely concealed.

Vent-a-Roof is fully compliant with the NCC requirements and has been tested to withstand Australia’s harsh weather conditions. It is an ideal solution for all common metal roofing types.

Rapid Ridge is a product suitable for tile roofs

Rapid Ridge is a product suitable for tile roofs, is easy to install, and facilitates airflow exactly where it’s needed most.

Solar roof ventilation systems provide all the advantages of powerful extraction while using the sun to power its performance.

These systems are extremely efficient and move thousands of cubic metres of air per hour. Furthermore, they are relatively easy to install but, like a whirlybird, which is similar in size and profile, it will show on a roof line.

It’s not just a roof or wall – it’s an opportunity

No1 Roofing are the premier manufacturers and stockists of architectural panels

Gone are the days when walls and roofs had little street appeal.

No1 Roofing & Building Supplies are the premier manufacturers and stockists of architectural panels which can enhance the beauty of any building and which can work in conjunction with natural ventilation solutions.

Genesis™ Standing Seam, Snap-Line45®, Eclipse™ Snap Lock, UrbanE™ Nailstrip, or Expression™ Interlocking Panel are laid directly over battens or a ply substrate and are held in place with concealed fixings - allowing for easy incorporation of bottom inlets and top outlet vents.

Wall and ceiling insulation acts as a barrier to heat flow and is an adjunct ingredient in creating a building with healthy air and lower energy costs. There is a wide range of options and price points.

Creating a building that is mould-resistant, comfortable, aesthetically pleasing and energy efficient will involve a mix of solutions, and finding those solutions will depend on the project.

Some solutions shown in this article can be retrofitted, but you must also consider the environmental conditions you are working in order to maximise the effectiveness of your choices.

No1 Roofing and Building Supplies has been helping builders since 1990 and is now one of the largest wholesale suppliers of metal roofing and cladding products in NSW.