Ventilating the roof space is key to improving thermal comfort in the home naturally and can save you money.
Passive ventilation is very effective and it’s free, but for it to be effective it needs to be designed into a new home with some thought. Passive ventilation in a roof space relies primarily on natural air convection—the upward movement of warmer air because of its lower density.
Natural convection allows the upward flow of air through any space. The air current can be maintained as a continuous flow of air through a particular space if intake vents are placed at a point lower than the intended area to where the warm air will rise to and escape from (such as the eaves on a roof). This will allow the cooler air available outside to replace the warmer air inside the roof space, which will then be released at the higher points in the roof i.e. out at the ridge. This convection of air occurs naturally. Convectional ventilation is most effective when close-to-equal amounts of ventilation intake/exit areas are placed at both the lower and higher parts of the roof, which avoids bottle necks.
Wind-assisted vent options such as solar vents and whirly birds can be used where air is forced or “pulled” out of the roof space, and these methods are becoming quite common and can be seen dotted across roofs in Australia. They are capable of increasing the volume of air exhausted from an attic space but only if adequate intake vents (usually soffit vents) are also used at the lower point and used in the right combination with the other wind assisted vents placed higher on the roof. These methods will have low/limited impact if there is not sufficient intake vents or enough whirly birds at the higher point to move the air through.
Imagine if there was a better way, where entire roofs could be fully ventilated with no ugly penetrations like Whirly Birds sitting up high on the roof – what if we told you there is a better way? A European system called Rapid Ridge is new and simple in its application and requires very little change in the roof structure design. This passive mechanically fixed system uses the whole roof to allow large volumes of air movement through the entire roof. This not only eliminates heat build-up all through the day as the sun beats down on the largest part of the house, it also means the house is much cooler when the sun goes down. When you get home in the late afternoon or early evening and turn on the air con to ‘max’ to achieve a reasonable living temperature, with the Rapid Ridge system installed the air con has to work much less; using much less energy to achieve thermal comfort. In fact tests have shown that this method of passive ventilation can reduce cooling costs by up to 43% in a typical home when compared to a home with a traditional roof utilising a closed ridge.
The Rapid Ridge Ventilated Dry Ridge System consists of four component parts that work together to securely hold the ridge caps in place, whilst allowing the roof to breathe with a continuous flow of air between the roof tile and sarking so the sealed building envelope is not impacted. Independent testing of Rapid Ridge by Sydney based ESD consultants – Certified Energy has resulted in a half star contribution under the NatHers rating system with the installation of Rapid Ridge in comparison to a home without Rapid Ridge. The Rapid Ridge system creates a natural convection through the roof space -starting at the lower end with cooler air entering through the eaves vents, then flowing through the whole roof space, and ending with the warmer air being naturally ‘pulled’ through to the ridge that is fully open, allowing it to escape.
The ridge tiles are mechanically fixed with a unique clip that has been designed specifically for the Australian roof tile market, including Boral and CSR tile profiles that also work on hips and valleys. To facilitate the ventilation and also deal with the elements, a special weather proof barrier is also used at the ridge and on hips and valleys, this has been CSIRO tested for weather dynamics. It consists of an advanced double labyrinth ventilation technology (patent protected) that provides both ventilation and protection from driving rain.
In essence, insulation is crucial in any home design for both heating and cooling the living space, and when used in conjunction with a passive roof system such as Rapid Ridge, significant reductions in energy consumption can be made, and therefore costs on cooling your home can be achieved more easily long into the future. So think ahead – as the ‘Your Home Government’ website on building sustainable homes says: “your money is better invested in an energy efficient building than spent on heating and cooling”.