It is self explanatary that roof air ventilators are used to ventilate a roofspace with fresh air exchange, however do most ventilators actually do this.
There are all sorts of claims for the attributes of different types of roof ventilators. It is my experience as a roofer with over 5 decades in the roofing industry that many roof ventilators do not live up to these claims or even work to move air at all.
I have seen the direct opposite to be true, with whirlybirds – I believe that with the constant spinning rather than remove any stale air from the roofspace they seem to seal themselves off.
I have seen them spinning full of spider webs that do not move at all, I have been inside the roofspace and felt no air movement within a whirlybird at all.
Of course any roof ventilator will need inlet air from another source to allow said roof ventilator to exhaust any stale air from the roofspace. It is my experience as a roofer that there are many roof air ventilators that do not have an inlet ventilator to allow for air exchange.
For example - it is supposed that a whirlybird should have four eaves vents for inlet air. If you look at most homes with whirlybirds and other roof air ventilators they are on their own without any source of inlet air at all – hardly anyone fixes eaves vents for inlet air.
So do you see my point if they did actually work with inlet air how can they possibly work without it.
However, in saying that I have seen all types of roof air ventilators that don’t even work with fully open eaves. There have been millions of dollars made from ineffective roof air ventilators.
So what is the answer to effective roof air ventilators – an inlet and outlet roof air ventilator of the same volume for each zone of the roofspace. 4 for a small home, 6 for a larger home and 8 for a huge roofspace accordingly so no matter what size of roofspace you need to break your roofspace into zones and have a pair of roof air ventilators for each zone. These roof air ventilators should be able to incorporate in their design the ability to harness the principles of fluid dynamics – the study of air and gases in motion including aerodynamics.
These are the ingredients for effective roof air ventilators.