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I can't tell you if they are good yet but we have included them in our contract on the advice of or consultant, I would also be curious to hear anyone's before/after experience with these, we are have a dark colour (ironstone) so maybe that is why whirlybirds were recommended.
what color is your roof and are you installing any sissalation of any type??
Generally the rate at which whirly birds remove heat is not enough to compete with the rate at which the roof creates heat.
I am in the progress of having my Monument roof installed. I climbed up on the celing space and touched the area under the sissalation on a warm sunny day and it was warm. I touched the actual colorbond and it was hot almost to hot to touch. So it looks like the sissalation is having some effect.
Joined: 17 Aug 2007 Posts: 1832 Location: Point Cook
Whirly bird is standard in our house.
And when it was installed, i noticed that no one in our area has it.
_________________ ----------------------------------------------------------------------------------------- Built the Nevada 42 Next project - landscaping!
Joined: 02 Apr 2007 Posts: 955 Location: North West Melbourne
We're paying to get one on the advice of the builder. We have plant and equipment fans at work which always overheated until we installed whirlybirds - they never broke down again.
we are having colourbond Dune colour for the roof, i don't thikn anyone in PD is goign to advise me on whether i should, but I will insist on sarking (foil reflective wrap) under the colour bond sheet, don;t know whether i still need the whirlybird.
Joined: 21 Jan 2008 Posts: 381 Location: Greenvale
A roof plumber mate of mine strongly recommended getting sarking but the builder advised the roof had already gone in. My mate then said that a Whirly Bird would suffice as we live in Melbourne, not Sydney or Brisbane. The installation of the WB was more to do with moisture and condensation in the roof, rather than the heat issue.
The way he explained it was that on a hot summer's day, the air in the roof gets really hot. Then, when the sun goes down and the tin roof cools down, the hot moist air condenses on the relatively cool underside of the tin and drips down on to your ceiling. This is more a problem in humid climates, but still occurs in Melbourne as well.
The WB's only really work if you have air vents to draw in cool air into your roof space (ideally from under your eaves- Sorry Matt ).
Sarking works by creating a moisture barrier, so that the moist air does not come into contact with the cold tin in the evenings.
Yes but if your read the content of it you would realise that the main supporter of it has no valid argument:
Briefly:
- hot air rises so it is not as hot near the ceiling as it is near the roof
- hot air actually doesn't contain a lot of energy to transmit through the ceiling
- in Summer the heating comes not from the hot air in the roof space but comes from the hot roof radiating heat directly onto the ceiling
- removing the hot air with a whirlybird doesn't actually deal with this problem
- the best way to stop the roof radiating is to use reflective foil
Lastly the best proof is actually in a real life experiment in a house where they put in solar powered whirlybirds. They discovered it only reduced cooling requirement by about 6%. Our usual wind-powered whirlys probably wouldn't even achieve that! I wouldn't waste my money. Anyway foil is cheap - $2/m2
You could prove it to yourself. Place a thermometer on both sides of a ceiling. The air temperatures are nowhere near the same. Very little heat energy travels through.
You could do a little experiment to show how well foil works. Get two cardboard boxes and line one with foil. Take them into direct sunlight for an house and compare the temperatures inside.
BOY, I started to read the link above but I don't have a spare 3 hours to go through the whole thing, because they are relatively cheap so if they make a very small difference I think it may be worth it when you consider the whole cost of the project.
BOY, I started to read the link above but I don't have a spare 3 hours to go through the whole thing, because they are relatively cheap so if they make a very small difference I think it may be worth it when you consider the whole cost of the project.
Exactly!
_________________ Demolition August 2009, Construction Started September 2009, Completed December 2010
BOY, I started to read the link above but I don't have a spare 3 hours to go through the whole thing, because they are relatively cheap so if they make a very small difference I think it may be worth it when you consider the whole cost of the project.
If you put foil in you will make a real difference. Actually about 20% reduction in cooling requirements. And it will be good for your air con system and as a condensation drainage plane.
Whirly's in a humid environment may actually be detrimental to moisture control by bringing in unwanted moist air into the roof space and rotting your timbers or rusting your fixings.
Joined: 31 Oct 2008 Posts: 1639 Location: Adelaide
BigKev wrote:
Dymonite69
I have read both sides of the argument and neither is 100% correct.
All that I did was put up a counter argument.
There are way too many factors to be considered before dismissing anything out of hand.
I can always change my mind with the right evidence! I would be interested to know your rationale for the value of whirlybirds. My position comes from two studies where the effect of whirlybirds were specifically examined and directly measured with temperature sensors (e.g. not hearsay or opinion or anecdote)
There is 2.4m2 of ventilated roof space to assist in reducing the temperature in this space. The large openings create air mass movement, which assists in removing heated air and replacing it with outside ambient air. Its impact on the temperatures in the living areas is minimal in Research House...."
This second study looked at powered fans and the effect on both roof space temperature and reduction in cooling load.
Joined: 25 Mar 2008 Posts: 370 Location: Adelaide Hills
I hope this isn't too far off topic, but I'm intrigued by the recommendations for reflective insulation.
A couple of factors that often seem to be ignored at the installation phase are:
1. The manufacturers state the sarking needs to be draped (ie hang down between the purlins) not pulled tight. I'm sure most of the time it is installed so that it is virtually touching the roofing material over the whole surface. Maybe the corrugations are the only way it ends up being effective.
2. The reflective surface is only on one side of the sarking. So how can it reflect radient heat from outside if it's installed the usual way with the reflective surface downwards?
Hopefully someone can shed some light on this.
Cheers
zeke
BTW, I'm fascinated by the explanation of why ventilating the roofspace doesn't help to cool the house. Drawing on my high-school physics from decades ago, I must admit it makes a lot of sense in spite of being somewhat counter-intuitive.
Joined: 26 Dec 2007 Posts: 4802 Location: South Australia
We have 2 whirley birds on a colour bond roof, steel frame home so moisture rotting the timber frame isn't an issue, anyway where we live it is hot and dry and windy, small outlay, seemed a good idea.
Joined: 17 Apr 2007 Posts: 3796 Location: Near the water
Zeek correct - Sisalation does need to be draped and correct many times it is not installed with a sufficient gap - therby reducing it's performance.
Dynamite - Theory from a couple of sources is all well and good - but be careful of the web not being all true and correct :d
So as a test of your theories -
Grab a section of silver sisalation (I've got new 60 metre roll if you need some) and on a hot day stretch it out over a metre square cardboard box and then measure the temperature inside (shade the sides of the box)
Do the same with another box at the same time with sheet of tin and some R3 or 4 insulation and tell which one works best.
Then you'll have a bit more measured data of your own - I'd be interested in your results - because my experience and data is not as you propose in your previous threads.
As for whirlybirds - I was in the old Perth gaol last weekend and the 1800's gaol has an excellent whirlybird that is a 3 foot diameter fan that vents the entire room through the roof. On a 27 degree day it was naturally spinning with the convected air that was moving through it.
The trick with roof ventilation, is to ensure that you are using it to draw air into the house, and venting out through the roof space ensures you create good ventilation, as well as remove the heat from the roofspace.
But it's better if the entire house is designed around it - not just an add on.
One option for existing houses or non ideal airflow designs is to use a system like the cardiffair.
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