Roof Ventilation Blog


Cooler Home during Summer Months

In all societies there are the gullible, the uninformed and the well informed.
The gullible, listen to whom ever has a little knowledge but far from what needs to be known.
The uninformed, are those who insist that whatever they think, or have, is the best.
The well informed, seek out the knowledge and implement it, despite their seemingly isolated social choice

That having been said......

Often it is presumed that just ventilating the roof is going to be sufficient whereas the reality it is only half the story which provides less than half the potential of keeping a home cooler naturally in the summer months.

Yes, venting the roof will reduce the overall heat retention of the building however the exercise is to be proactive and make living conditions comfortable in the rooms below without incurring the high and higher cost of using an air conditioner

Obviously those with 2.7m ceilings are going to have a cooler rooms longer than those with 2.4m ceilings and 3m ceilings cooler again

Those with raked or cathedral ceilings will have a situation proportional to the height of the roof and the resistance (insulation) contained within.

To begin with the homeowner needs to feel confident that the concept of ventilation is a worthwhile and is a cost efficient exercise.

To explain this simply consider the following,

Fill a bucket with water and obviously if you put a hole in the bucket the water is going to escape. The bucket will empty proportional to the hole, the bigger the hole the faster the escape.

This is the physical principle governing the escape of water in a bucket

The physical principles governing heat in a room is the inverse, or opposite to, water in a bucket

Turn the bucket upside down like a hot air balloon and pour heat into it, the warmest air is going to be at the top of the air balloon, which is the energy that causes a hot air balloon to rise

If you put a hole in the top of the air balloon the heat is going to escape and down comes the balloon.

Ventilating a roof, is precisely that, allowing the heat to escape so it doesn't build up in the form of back pressure and transfer into the rooms below via conduction

The hole is what all escapes through.

The efficiency of the hole is governed by the device placed over the hole.

This is called a roof ventilator......and all roof ventilators are not equal

To gain the optimum performance out of roof roof ventilation refinements.

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart


How to ventilate a raked ceiling

Rooms with raked and cathedral ceilings have one common problem during the summer months ....they get hot slowly... and they stay hot longer.

Obviously venting the heat out is the answer, but how to do it without creating other issues as a consequence.

Remember heat is energy just looking to be released and you want a roof ventilator that does just that

First you select a roof ventilator or cupola, the size of which is determined by the size of the room and the means of low level air ingress (via door and windows)

Then you match it with a ceiling vent or register that can be opened and closed at will, either manually, push / pull with a rod of suitable length, or if it's too high with a electrically operated ceiling vent via switch or remote controlled.

It's advisable to choose a ceiling vent or register able to be opened incrementally so that it can be used to freshen the room at varied times during the year as occasion requires

The difference experienced as a consequence of the installation will be quite remarkable, a different room altogether especially if the room is on an upper level. The roof ventilator chosen in such a case will need to be larger as the total heat load of the house will be trying to get out of the roof ventilator/ cupola

It may seem like an unwelcome expense but ventilation properly done will be well worth the transformation

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Venting the top floor

The venting and cooling of a double story house is more complex than a ground level dwelling.

The common statement heard made by owners is.....'I only want to ventilate the upper level as the ground level is cool, so that area doesn't need it!'

well of course it doesn't need it, it's cool as a consequence of the heat migrating to the upper level....all the heat absorbed by the whole house has moved up into the upper level....even the heat off the downstairs refrigerator coils has moved you could say that the upper level has the combined heat load of the whole house, making the exercise of venting the upper level more critical.

In the quest for making our homes more naturally responsive in maintaining comfort levels, and reducing costs, one need to apply a little logic and common sense

Electricity costs are going to go in one of two directions, ......and down is not one of them.

So there you are, a high heat load in the upper level and the concept of cross ventilation isn't working for you.

Bedrooms are hot, no one is getting any sleep and what makes is worse, there's a cool breeze outside where the temperature is several degrees cooler.....and none of it is coming inside.

What to do?....other than rip off the roof.

Unless you've been able to master the art of blowing air into a bottle you're faced with the reality that the only way you are going to get the cool air to come inside is to let the hot air out....and the best way of getting the hot air out is straight up install on large roof ventilator or cupola...not some mickey mouse product that works on solar power and you delude yourself that you're going to get free power

If you were to punch a hole in the bottom of a full water tank you wouldn't use a pump to take the water out.

So too the roof, once there's a nice big hole, the heat will come barrelling out.

That's the roof space/attic area taken care for the rooms.

A ceiling vent placed in each of the rooms which will allow the heat trapped above door heights to escape into the roof space....and as it's escaping, it draws the cooler air in from outside to replace it.

You can't remove one thing without replacing it with another...even if it's air.

Like I mentioned....ever try blowing air into a bottle?

The ceiling vent ideally needs to be adjustable, preferably with a push / pull action, so you can open and close it incrementally. Whatever you do, I suggest you DO NOT USE A PLASTIC TYPE....they break easily and at the worst possible time and you have to replace the whole unit...if you can find one

Metal ceiling vents or registers come in two types, manually operated, using a rod of appropriate length with a hook, and 12v electrical, with a remote option.

Not only do you vent the room(s) naturally but you end up with fresher and cleaner odourless rooms because you are introducing fresh clean oxygen

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Roof Ventilation Fans

The idea of a fan in the roof for the purpose of venting the heat out is a seemingly attractive one.

Note, the fan being used here is a 240v axial or centrifugal fan not a solar whiz bang

There it is, 'a fan sucking the heat out'...... fantastic...modern day roof ventilation......if only the Romans had them.

The fan sucks the heat out of the roof, (I say sucks as it's the term the sales people use) and it obviously draws ambient air in to replace that which has been removed, using the path of least resistance.

So ideally the ingress points have to be the furtherest away from the fan so as to air wash the distance in between the two points, and the ingress (eaves vents) need to have minimal resistance as the ingress efficiency is going to affect the venting efficiency of the fan.

In the case of a ventilating the roof space of a skillion roof, where the distance between ceiling and roof lining can be as little as 200mm having a dedicated ingress with a fan at the opposite end, there would be some benefit in both relieving the heat gain and offsetting the saturation of the ceiling insulation.

So bearing in mind that the average roof space temperature is around 68 degrees and the heat transfer via conduction of the steel roof will be proportional to the airflow of the fan.

How long is the fan going to last given that manufacturers such as EBM Papst and Zeihl Abegg do not recommend their fans be used beyond 60 degrees

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Roof Ventilation Fans pt 2

The prevailing wisdom would seem to be against using fans for venting the heat out of the roof, particularly during summer months as regards to operational life and efficiency of the fan.

Of course there is nothing to prevent you from using a fan(s) for air ingress (eaves) into the roof space as the ambient air flowing over the motor is never going to be critical and as long as the roof ventilator does not create too much resistance so as to cause the fan motor to overheat, then it could be considered an alternative in creating a positive flow in ventilating the heat out of the roof space.

In all cases the roof ventilator needs to be able to cope with the flow required to ventilate the roof efficiently and the duty of the fan needs to be proportional to the release as a pressurized roof under these circumstances is something to avoid.

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Sub Floor Ventilation

The purpose of venting the area beneath a timber floor is to prevent the incidence of wood rot and consequential odour arising from high humidity levels caused by lack of sufficient ventilation as my be required to remove moisture gain.

One needs to remember that all space needs to breathe (ventilate) The space under a timber floor is one such area, however it should be noted that a vented sub floor area will always be cooler as a consequence.

A moisture barrier can be employed to partially address this problem however the necessity to vent the area will always be required.

Obviously the most desirable form of aspiration or venting of an area is a natural one, where thermal and pressure differentials about the building perform the task of ventilating the area as is required.

Natural ventilation is often referred to as 'passive' by those wanting to sell you a powered 'positive' ventilation solution inferring that passive is equal to submissive and therefore not as effective.

There's eating and there's overeating....and as with anything overdone there are always unpleasant consequences

The more open the sub floor area is, then obviously the more efficient the ventilation, however there is a level to which sufficient ventilation is considered appropriate and going beyond that point can often lead to adverse results. The more the better attitude regarding sub floor ventilation, or any form of ventilation in fact, is not a wise one.

In many cases the sub floor area is going to be difficult to assess due to inaccessibility and this is where you may find yourself at the greatest disadvantage because the assessment of the problem may simply be the result of conjecture and supposition.

There are tell tale signs of certain conditions arising from poor ventilation being obvious to someone who is experienced in these matters. You will not know, so it is important that the assessment be presented to you in writing, so that if you need to get or want a second opinion you are not trying to think of what was said previously.

When a sub floor venting problem presents itself it is imperative that the prevailing dynamics causing the lack of appropriate ventilation be understood before any solution is proposed or implemented.

In any efficient natural venting solution there are ingress and egress points as may be required to facilitate a balanced displacement of air in the area.

A ventilation professional will never proposed a fan be used from the outset, as a ventilation fan can never be considered a solution. It can be a refinement to a venting solution but never the solution in and of itself.

If the problem is caused by poor water drainage, as are most, then the obvious solution is addressing the drainage, not putting in a so called 'turbo vent fan' as a band aid. This product fail, and require continual replacement, due to moisture degradation .

The obvious outcome being the salesperson's got the money and you're still stuck with the problem....'Oh yeah but',.... 'we tried', ....'wait 'til next season and see how it goes'....'give it a chance to dry out', .......doesn't quite do it.

A product is something that is purchased and employed where a problem arises out of poor building design and no means of rectification is available.

The so called solar, or packaged products, require careful consideration as their performance efficiency and work life needs to be questioned.
A packaged product is one that is sold and claimed to be suited to all situations.

It is not a solution designed specifically for your situation

Forums are useful up to a point but there is no guarantee....just opinion,
and you are going to spend money based on this opinion

Where fans are used for assisting in the venting of such areas you have a choice of 'negative' or 'positive' modes

Negative venting is where the fan is employed in a exhaust duty in drawing the air volume out of the sub floor area and the supply is via fixed vents of various size to position are used for ingress.

Positive venting is where a fan is used to fill the sub floor area and discharge occurs with the same size to location fixed vents.

Ideally the fixed vents should be of stainless steel irrespective of aesthetic colour

There are other more specialized venting themes one can use depending on the circumstances and nature of the building

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Roofing Materials

Tile v Steel

There are principally two categories of roofing materials that can be said to be 'the crown' on a house.

Steel sheet and Tile substrate (clay, concrete, slate etc)

The oldest of these being clay tiles developed over the ages virtually in conjunction when man was able to control fire with the clay tile being the consequence as regards to roofing materials. The concrete tile development arriving at a later stage in the evolution of building materials

So let's imagine that the corrugated iron sheeting was developed at the same time, which material do you suppose would have been used?
The tile, simply because the fasteners required to retain the sheets in a water tight fashion would not have existed.

I think we would all agree that kiln fired tiles were used, not because they were the best but simply because they were the only commercial product available in the evolutionary cycle.

Initially there was the galvanized corrugated iron roof sheet, was limited in size and it was used in much the same way a large tile, under and over with an overlap on the side

When you look at cost and speed, a metal roof is constructed faster than a tile roof. Both materials have their respective advantages and disadvantages

Today steel roof sheeting comes in continuous lengths to suit the roof, the most common being the corrugated profile, whereas tiles are much the same size as they have always been albeit that their contour profiles are more numerous and are considered to offer greater initial aesthetic choice.

The unfortunate aspect regarding colorbond is the surface integrity of their colours.
Within two years the surface integrity begins to dissipate and begins to acquire a chalky finish, which can be deemed acceptable, if it's all the same batch but not so great if dissimilar products (guttering eg) of the same colour are used in the construct.

A tile roof absorbs and attenuates (stops) sound whereas a steel roof unfortunately transmits sound much like a drum.

Regarding heat transfer, a steel roof does not store heat and sheds any heat load the minute the sun sets, whereas a tile roof absorbs and retains heat load for a longer period of time. This can be considered as being beneficial with a tile roof during winter which can be offset by efficient roof ventilation during summer.

Today many of the shortcomings can be nullified with the use of insulative and absorptive materials so the question becomes more relevant,...which is the better material to use?.

Some would say steel is lighter, tighter, cleaner, flashings are simpler to apply. One needs to be mindful that the trades aware of the traditional and the proven modes of flashing techniques do not exist any more and there is a need to consider future maintenance as may arise.

As regards to ventilation, whether it be roof ventilation or room ventilation, the versatility is better with clay or concrete tile as opposed to steel, as a clay, concrete tile roof is easily repaired via replacement, and as stated previously, has better sound attenuation qualities particularly when it rains.

One singular forte of a steel roof is it's suitability to roof pitches under 12 degrees

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Insulation Realities

The purpose of which is to limit heat loss or gain.

In domestic and general buildings, during winter months, to limit heat loss through the ceiling and walls where the manner of construction consists of a thin membrane material such as plasterboard as a lining.

Its corresponding performance during the summer months comes with a plus minus effect, in that the greater the amount of insulation, the greater the storage potential, therefore the longer the building will take to purge itself of the heat load during the evening cycle.

The house is less resistant to ambient change

Various entities including govt. based organisations will attempt to suggest that insulation will provide all the necessary comfort levels desirable but disappear into the wilderness when asked to show their rationale, or attempt to change the narrative.

The reality is that there is no advantage without a corresponding disadvantage and anyone advising differently should be questioned as to rationale.

Bigger is not always Better!

In most conditions, the use of an insulative medium above r3.0 is not warranted and even then should be used in a manner so saturation is avoided, and in the roof space appropriate venting should be employed with any high heat load absorbed being dissipated quickly and efficiently.

A decision should never be made until full awareness has been acquired.

Unfortunately there are those that think that when a word ends in ‘ion’, one is a substitute for the other.
A dangerous presumption!

Insulation, Ventilation, Air conditioning have totally separate areas of function and one does not replace, and or, is a substitute for, the other. Just as do the tyres, steering wheel and brakes in a car.

In simple terms:

Insulation – is like putting an on overcoat, to prevent heat loss or gain
Ventilation – is like breathing
Air Conditioning -cooling -a cost based climate system controlling living conditions reliant on consumption of electrical energy with or without water.

Putting on an overcoat is not going to make you breathe any better,
and the air conditioner is not going to improve the quality of air.

Conversely, breathing well is not going to make you any warmer, but it will contribute to your remaining cooler, and is guaranteed to keeping you healthier.

Use the right product for the right reasons and avoid trying to demean the validity of the product, or approach, on the basis of financial outlay because in the end you are the one that is ultimately going to wear the outcome

As with anything, a solution based on comprehensive understanding always produces the best outcomes.

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Conjecture & Supposition by Isa Stralian

There was a time early in my career as a designer specialising in new materials and processes, one of them being sound absorption and attenuation, when I was asked to investigate a situation where a woman was complaining of a high pitched noise in her area causing her untold grief when attempting to sleep in the evening

The University had gone out with their sophisticated noise detection equipment and found nothing. It was presumed at the time that she may benefit by sound proofing her room in an appropriate manner.

After a couple of interviews with the woman where she was obviously distraut and beginning to believe that she was being fobbed off by all and any involved....the city council, the EPA, the University.

I assured her that there was no doubt in my mind that she was hearing what she claimed to be hearing, but would she indulge me by visiting her dentist and asking him to check the alignment of her teeth as regards to pressure on the nerves.

Because she had a molar removed some six months prior her her jaw began to misalign and her teeth were starting to grind causing uneven pressure on the nerves connecting to the aural canal.

The teeth were corrected, the jaw realigned and the distressing sound gone.

I make mention of this experience so as to amplify the fact that all things may not be as they initially seem and very often the answer may be elsewhere.

I can only emphasise that the proper assessment of any problem is essential to determining the correct solution

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Roof Ventilators Explained by Isa Stralian

Let's start 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.

The function 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)

In order 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.

So there 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.

The best 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.

Then we 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.

The performance 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.

The variations 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.

Then last but not least you have the Cupola style, as seen on many a gracious residence.
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.

Today the 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.

Usually 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

True cross flow venting is more suitable and any device simulating the effect of low velocity and high displacement is preferable

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Overhead Sweep Fans

The high displacement slow speed fans are used quite extensively in the tropics where the humidity is high and moisture quite plentiful particularly on the surface of the skin.

The gentle movement of any breeze would cool the capillaries if the skin and make conditions more bearable during the wet season in particular.

The original sweep fans employed in the tropics were placed someway down from the high ceiling and avoided drawing the warm air uppermost to the region below.
Today's' overhead fans are some thing quite different in that their location is quite close to the ceiling, drawing the warmer volume into play and their displacement capacity being quite low at slow speed has a detrimental effect on an individuals skin when exposed for prolonged periods of time at the higher speeds

Initially the capillaries secrete token moisture imparting a cooling effect however when the skin is no longer able to surrender any more moisture the skin becomes dry and dehydrates.
This is evident particularly if left on when sleeping, children are thirsty midway through their sleep cycle and women complain of dry skin on their faces and arms.

The overhead sweep fans need to be used prudently as they do not improve the quality of the air as does ventilation.

Very often ventilation is perceived as air movement whereas it is in fact air replacement through movement

Their use as an alternative to ventilation is based on poor assessment and again an attempt to use one medium as a replacement for another.
The reverse motion used to reintegrate warm air with cooler during the winter months has the same effect except the dehydration occurs at a faster rate.

The circulatory function is suited more to outdoor use rather than indoor as natural currents that arise from moment to moment assist in the ventilation through displacement

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Ventilating Bedrooms

One of the problems all homes have where children, particularly those of adolescent age, is odour.
Whether it be from socks, shoes or general hormonal secretions, bedrooms tend to get on the nose, particularly where the occupants are involved in high activity sports.

Added to this if the rooms have low ceilings and little air ingress to air wash the rooms. Ventilation in these rooms is essential ensuring the odours are not absorbed into the furnishings.

Ceiling vents and ceiling registers are an ideal way of keeping the rooms fresher by venting into the roof space, allowing the odours to remove themselves.

This venting is aided by the roof ventilator ensuring even the smallest flow, called trickle flow ventilation

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart



Evaporative Air Conditioning

Condor Ventilation has released a ventilation system that allows owners of evaporative air conditioners to have doors and windows closed when using their systems and not have their security compromised.

By channeling the air up into the roof via pressure responsive air relief ceiling register/s and or through adjustable ceiling registers, and out through a specially designed Condor roof ventilator you are able to maximise the return on your running costs and in fact reduce overall consumption.

The Condor Roof Ventilator also functions as a stand alone unit in that it ventilates the roof independently when the air conditioner is not operating. This function also reduces the demand on your air conditioner, not to mention reducing the heat pressure on the ducting. The roof ventilator is heat & pressure driven, so you will minimise heat load loss during winter. There are no moving parts to maintain or replace. Insulation is not overloaded and reduces heat permeation on ducting

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart


Venting under a Skillion Roof

A skillion roof on a house is a shallow pitched roof usually pitched between 1 - 7 degrees and is usually quite low offering the minimal permissible height of approx 2.4 metres.

Any area below this type of roof that requires venting during summer can only be done successfully by venting direct to atmosphere, much the same as venting a raked ceiling.
This method requires a roof ventilator on the roof with an operable/ adjustable ceiling vent installed on the underside so as to control the air flow through it.

The ceiling vent employed needs to be a highly efficient type that allows a high flow when required and not some mickey mouse plastic product out of a hardware store that works poorly to begin with and not at all when dust gets into the mechanism and breaks as a consequence.

If you're going to go the trouble of spending money, do it properly, instead of on the cheap, because it will come back and bite you, at the worst possible time.

Ventilation solutions will differ between Brisbane, Sydney, Melbourne and Hobart