Before we answer the question of “Does roof ventilation work?” lets talk about insulation.
Believe it or not, the ancient Egyptians were the first to use insulation with the use of asbestos. As we all know now, it wasn’t the greatest idea, James Hardie could have blamed the Ancient Egyptians perhaps, anyway insulation has come a long way since, and it’s now quite safe and affordable and in most cases, easy to install. Insulation works because it traps air, but the air must be still for it to work.
Now, having said this, the whole idea of connecting your home to your roof area, to assist with controlling mold “inside” and extreme heat is a terrible idea for the following reasons:
- Non-powered Roof Ventilation can move an almost insignificant amount of air. You’ll notice how it’s never actually documented how much air they can move. Solar/Electric roof ventilation can move more air but it has problems depending on the seasons, and reducing gaps in insulation is still way more efficient.
- The area inside the roof, with roof ventilation or not, achieves extremely high temperatures in summer and freezing temperatures in winter. The difference in temperature is small, and when insulation is in place, the difference is even less.
- Your ceiling airtightness and insulation consistency are of paramount importance for heating and cooling. Insulation on top of your ceiling reduces the effectiveness significantly of having a slightly reduced temperature in your roof area during summer. So in other words, before insulation was around, whirly birds/roof ventilation did add value during summer, but not anymore.
- Using inside air via ceiling ventilation to feed a roof ventilation device, encourages hot summer air from outside via windows, doors and other points of air leakage to come inside, overloading your air conditioning system. The home does not have an endless supply of cold air available for ventilating through a whirly bird.
- Humidity also comes from outside. Extremely ventilated homes are just as susceptible to mold as air tight non-ventilated homes. The best solution to fixing mold problems is installing, effective and efficient ventilation, that should also reduce temperature swings inside the building. Humidity sensor fans in the bathroom with door ventilation grill, and practical use of an externally vented kitchen range hood. Exhaust fans need to be installed in a way to allow sufficient air to move the humidified air out quickly. Putting a vent in the bathroom door allows the fan to leverage from air leakage throughout the whole house, instead of just the bathroom.
- Much like evaporative cooling vents, if you install a vent inside your home on your ceiling for hot air to move up through a Whirlybird, you will need to get up on a ladder to close it and open it a few times a year, which could be risky, especially for the elderly. These installed vents may not be very air tight when they are closed up.
- In winter, moisture can be a problem in the roof, make sure bathroom fans and kitchen range hoods are ducted directly to the outside via the tiled or a metal deck roof. Roof ventilation devices are not a full-proof way of getting rid of this high humidity air which can cause moisture problems in roof cavities.
- A roof ventilation device with indoor ceiling ventilation can contribute to additional pollen getting indoors causing health problems such as hay fever or asthma attacks.
Before insulation became commonly used in Australia, old roof ventilation devices used to have Fans inside them, but nowadays most versions do not. In homes/sheds that have no ventilation and insulation, a Roof ventilator could make a difference especially if roof ventilator is motorized, but in today’s modern age of insulation, in residential homes, they are no longer of viable benefit in the majority of climates. If you wanted to ventilate a roof cavity right, Ridge cap ventilation, along the whole ridge is capable of moving much more air with a much larger surface area opening. For surviving the heat, relying on Insulation and air tightness is a much more logical way to go, especially in places where temperatures can drop quite low at night or during the winter period.
Table of lack of benefits
|No insulation with ceiling/wall ventilation grills in the plaster||Not Beneficial. Brings uncontrolled cold air inside from outside. With a colder ceiling surface, more energy will be used to warm the house.||May be beneficial, occasionally depending on your climate.|
|No insulation with "NO" ceiling/wall ventilation grills in the plaster||Not Benefical. With a colder ceiling surface, more energy will be used to warm the house.||May be beneficial occasionally depending on your climate.|
|Insulated ceiling with ceiling/wall ventilation||Not Beneficial. Brings uncontrolled cold air inside from outside||Does not work effectively|
|Insulation with no ceiling/wall ventilation||Not Benefitial||Does not work effectively|
|Windy||Not Beneficial. Brings uncontrolled cold air inside from outside||Brings uncontrolled hot air inside from outside|
On the internet, solutions are put forward to install a vent on the ceiling that will then feed hot air from your living area into your roof area and then out of the Roof Ventilation device.
Be careful, very careful with these solutions.
Positive pressures that may come from an unsarked tiled roof exposed to the wind and/or hot air expanding means that ventilation to your roof area can move into the home via any internal ceiling vents or other recessed electrical devices that are ventilated into the living area.
During winter, with ventilation, you get a colder roof area which means you lose thermal gain from a warmer roof area, but if you have a well-insulated ceiling, this “benefit” is locked out anyway.
For a comfortable home, insulation is the ultimate. If you have condensation forming inside your roof area, install a more effective ventilation system like ridge ventilation.
Table of hot hours compared to cold hours in a year.
|Country||the amount of hours with temperatures BELOW 10C||the amount of hours with temperatures ABOVE 30C|
Concentrate on the insulation consistency and airtightness of the building envelope, rather than complicating your building envelope and trying to leverage off the possibility that more comfortable air could be leveraged from outside. In bathrooms and kitchens, think about good strategic ventilation, by thinking about where the humid air is leaving, as well as, where the air is coming from to get that air directly outside.
A more constant/comfortable temperature you have inside the house is key to reducing mold, and the best way to do that is with insulation consistency combined with decent air tightness inside the building envelope.
One area, where roof ventilation can be useful, is in roof systems that are installed with sarking/sisalation. Due, to the lack of air flow, moisture can be a problem inside these types of roof systems. However cooling the home is not something they can do. Insulation consistency is what makes a real noticeable difference, click here to find out more on what to look out for.
Improve comfort directly, as opposed to indirectly with roof ventilation. Insulate right, Ventilate right, and then go energy-lite.
By John Konstantakopoulos
Dr. Mark Dewsbury from the School of Architecture & Design, UTAS, has been exploring many issues around energy flows, ventilation, and condensation within unconditioned and conditioned rooms and roof spaces of Australian homes. The research has highlighted many myths and anti-science beliefs about roof space thermal dynamics.
Mark Dewsbury (Ph.D.) | Lecturer & Building Research | School of Architecture & Design| Faculty of Science, Engineering & Technology