Most Australian homeowners give little or no thought to the roof cavity it’s out of sight, it’s not causing any problems as long as the roof isn’t leaking so it gets relegated to the back of the mind. But the thing is, a roof cavity that’s not getting enough ventilation isn’t invisible in its effects. It shows up in higher power bills, it shows up in air conditioning that can’t keep up with the heat, and eventually after years of quietly doing its damage it shows up in that lovely sign of mould on the ceiling and moisture damage to the roof framing that’s a real pain to fix.
What’s Actually Going On Above Your Ceiling?
The Your Home guide has found that, in homes with poor ventilation, roof cavity temperatures can easily reach 60 to 70 degrees in the summer. At that sort of temperature, the heat just keeps on transferring straight from the roof down into the living areas, putting an extra load on the air conditioner that just keeps building up over a whole cooling season. And that makes a massive difference an air con working with a ceiling temperature of 65 degrees is just not the same as one working in a space where the ceiling is a nice cool 35 or 40 degrees because of proper ventilation. The difference might not be immediately obvious, but it’s in the size of that power bill.
Winter brings a different set of problems though. Moisture from all the things we do in the house just keeps on moving up through the ceiling and into the cavity, where it just sits around if there’s no airflow. And that moisture is like a ticking time bomb it encourages mould to grow on the framing timber, it makes the insulation all soggy and compressed, and worst of all, it starts slowly breaking down the timber which only then becomes a major expensive headache.
The Ventilation Options And When They Work Best
The old wind-driven whirlybirds that a lot of people have on their roof will pull air out as long as there’s wind around. They can work pretty well in areas where the wind is usually blowing, but when the wind drops out and that’s often exactly when you need them most they just stop working.
Meanwhile the solar-powered roof fans are entirely independent of the grid and will keep on working even when it’s hottest out, which is exactly when they’re needed the most. They’re also really good in places like Perth and rural Queensland where the sun beats down all year. Plus, because they work independently of the wind, they can keep on doing their thing even when a whirlybird just couldn’t.
And then there are the full-on roof ventilation systems that you see in commercial buildings and high-end homes. They’re usually needed when there’s just too much heat or moisture for a passive or solar solution to shift on its own.
Signs That Your Home Has A Problem
There are plenty of signs to look out for before it all starts to cause major damage:
- The air just feels stale even with the air con on.
- You start to see mould on the ceiling or in the corners of the rooms that are right under the roof.
- Your energy bills are suddenly a lot higher than anything else in your area.
- You can see that the roof vents are blocked or missing.
- Just doing a quick visual check of the vents is usually the fastest way to figure out what’s going on.
The National Construction Code of Australia defines eight climate zones, each requiring distinct ventilation needs. While the system used in temperate south Australia may not be sufficient for Perth, Darwin, or central Queensland. In addition to being important inputs prior to purchase, these include the roof area, direction of the ridge, type of insulation, and soffit ventilation in place.
