Articles for the Home Consumer

Choose The Right Roof Ventilation System For Your Home: Tips To Help

Every home needs a roof ventilation system to ensure that air can circulate freely in the roof cavity.

With efficient circulation, stale moist air is ventilated outside and fresh air is drawn in. Your insulation works efficiently because it remains dry. This will have a positive impact on gaining energy efficiencies in your home.

Unfortunately, modern homes are designed and built to be airtight: the goal is to lower power bills. Without a passive roof ventilation system, moisture may continually enter the roof cavity, with no way to exit. This is dangerous for your home: moisture causes damage. Mould infestation occurs and this is dangerous to occupants.

You need a roof ventilation system even if you have extraction vents

If your home has extraction vents, you may feel that that’s all that’s necessary.

Regrettably, extraction vents may be doing more harm than good. Here’s why: condensation. The FAQ on Vent Systems’ website reports:

“Many mechanical ventilation products focus mainly on the ventilation of habitable areas… many of these systems have extraction vents in the habitable areas of the building that terminate in the roof space… The condensation from the habitable areas of the building are literally transferred into the roof cavity.”

The constant extraction of moisture from the house into the roof space, combined with inadequate roof ventilation, is a recipe for disaster.

The solution to moisture and condensation: passive roof ventilation

Whether your home is older or modern, you need a system of passive roof ventilation. “Passive” roof ventilation works via non-mechanical means to continuously circulate air in your roof.

Vent Systems recommends passive ventilation for all roofs, because:

“…every roof that is not passively ventilated may suffer from internal moisture issues depending on a number of factors.”

Let’s look at some practical tips to help you to choose the right roof ventilation system for your home.

1. Choose a passive roof ventilation system: it mitigates dangers

In Build magazine Issue 166, Stephan Rupp and Manfred Plagmann, BRANZ Building Physicists, warned of the danger of too much moisture in your roof.

They said:

“In most cases, the transport of moist air from the living area to the roof space is the source of moisture. The inadequate roof ventilation is then unable to cope with this moisture load, resulting in corrosion and mould inside the roof space.”

By the time the home owner realizes what’s happening in the roof cavity, considerable damage has already occurred.

2. Achieve cost benefits with passive roof ventilation

Passive ventilation specialists Vent Systems report:

“When compared with mechanical ventilation systems, passive ventilation is relatively cheap and inexpensive as there are no ongoing running or maintenance costs after the initial install.”

3. Building your home? Check your roof space ventilation and install what you need

Depending on the home, retrofitting a system to an established home can be expensive. Installing a passive roof ventilation system during the building phase makes sense.

4. Doing it yourself? Remember replacement air needs to be fresh air

In a Build magazine article, Issue 152, on “Passive roof ventilation”, Stephan Rupp, BRANZ Building Physicist suggested:

“… avoid situations where exhaust air, for instance, exiting through a ridge vent, is sucking up moist air from the living quarters below. The replacement air needs to be fresh – outside air coming through vents around the eaves for instance.”

If you’re installing your system yourself, map your desired airflow through your roof cavity. You goal is to keep air circulating: to extract moisture-laden stale air and bring in fresh air from outside the home.

5. Get expert advice: it’s worth it

When you’re installing your roof ventilation system, you need to consider not only your roof style, but also factors such as the volume of the cavity.

As Manfred Plagmann, BRANZ Senior Physicist reports in Build magazine Issue 157, you need to balance:

  • The outdoor climate;
  • Roof space climate; and
  • Building function.

Taking advice from a local roofing specialist familiar with local conditions makes sense and may save you both time and money.

Your specialist can advise you on what products you need and install them so you get the results you want.