by Isa Stralian
in mind the function of a roof ventilator is to allow and encourage
the air in the roof space to refresh itself.
It is somewhat
of a buffer zone against excessive heat and moisture retention
and allows the area below not to be subjected to what could
be considered as nature's impact in both heating and cooling.
cathedral ceilings however are another matter and require a
more specialized approach regarding roof ventilation.
off with the so called wind driven Whirly, Whizbanger, Spinner,
generic rotary ventilator fabricated in aluminium. Some rotate
on bushes, some rotate on plastic bearings, some rotate on steel
bearings.....and either way they are going to rotate easily
because there is little mass (weight) to them.
of this type of roof ventilator is to create a negative pressure
in the roof by drawing out a volume of air proportional to the
rotating speed of the rotor (the spinning part)
for the rotor to be effective, the distance between the rotor
and the spigot cannot be any more than 3mm. If it's greater
then the air that would normally be drawn up from the roof by
the rotor is going to be short circuited and drawn in through
the gap between rotor and spigot, thereby nullifying the potential
of the rotor.
you are in the hardware store, you spin the rotor of the roof
ventilator forgetting that the potential of what you are looking
at is in reality half, because the surface area of the other
half has got pressure against it, and air can only escape from
the area on the negative, or non pressure, side.
rotary ventilator in Australia was the Western Rotary which
was made in steel, rotated on lubricated bushes and could suck
like a hungry goat. This unit was last seen some 35 years ago
and replaced by the inefficient product as seen today.
have the pressure responsive roof ventilator which is made and
sold under many names and referred to as a 'passive', 'static',
and anything that implied that it was less dynamic than the
zip zap whizbanger whereas in fact operates far more consistently
than it's 'active' cousins.
of this type of roof ventilator is governed by heat and pressure
and the flow rate is proportional to the 'free air' area of
the ventilator. Now the roof ventilator size may be a x c in
size but the flow potential may well be 1/3 of that, and just
like it's cousin, it's efficiency is governed by side opposite
the pressure face.
encountered by this type of roof ventilator are far greater
and what makes them more attractive to the architect and homeowner
alike is their benign appearance.
but not least you have the Cupola style, as seen on many a gracious
This type of roof ventilator was the precursor to those seen
today although the presence of the Cupola design is quite distinctive
and regarded as the finer touch on the 'crown' of the residence.
Cupola is used as a services hub to where all exhaust ducting
is terminated as well as performing the task of venting the
roof and keeping the dwelling cool.
mounted centrally and straddled across two or more planes on
the roof although appears more functional than ornate as those
of the past historical roofs in architecture