The Building Code of Australia is looking at giving "whirlybirds" (Roof Space Ventilation) a mention in the 2006 BCA, allowing builders in the warmer zones to substitute whirlybirds for the more conventional ceiling insulation.

I think this will be a big mistake and cause a lot of people to install, or retrofit, these devices at considerable expense when I believe there is absolutely no evidence that they work.

The building industry is in love with whirlybirds, including professionals like architects (who should know better), but that doesn't alter the facts.

If any participant of this forum has evidence/opinion to the contrary, well feel free...

I have a couple of whirly birds on my weekender shed and they are always spinning in the wind providing roof ventilation. As yet they haven't let the weather in and we have some fierce storms in the past.

The problems with whirlybirds are that the heat you get rid of in the summer, is the very same heat you want in the winter. We have a couple of vents that can be closed to stop too much heat loss, but it's far from a sealed system.

If they say the whirlybirds can replace the ceiling insulation, that is a completely different story. The ceiling insulation is the very thing that stops the beating rays of sun from heating up the house and minimises the heat loss in winter.

The BSA must have gone mad, however most states require an energy efficiency rating on any new house design (varies in each state) before it can be approved. The loss of ceiling insulation would be a big ratings negative, but I guess the extra efficiency can be made up else where. Seems Silly Though.

Hi Jonno - what evidence have you got that these devices DONT work?

TB

G'day TB

One reason why whirlybirds don't work is that the incoming radiant energy is maybe 100 times the rate whirlybirds can suck it out. That's assuming no reflective barrier insulation under the roofing material. But even with reflective sarking, radiant input is far greater, relatively speaking.

But even that's not the correct answer, because it doesn't matter how hot the air in the roof space gets, because there's no mechanism by which it can transfer its energy to the ceiling and raise its temperature. And it's the long wave (infra red) radiation from the ceiling that makes you feel uncomfortable. If your ceiling is warm to touch (on a sunny day) then you probably don't have an effective radiant barrier under the roofing material.

As air is transparent to thermal radiation, it can only get heated by conduction. But you've got to have convection to speed up the conductive heating of air and convection can't happen when the energy is being pumped in from above and the roof space is essentially a closed box.

The air in the roof space can only get heated by contact with the underside of the reflective sarking under the roof material. And because it is warmer relative to the lower layers of air in the roof space, it is less dense, and thus buoyantly trapped under the highest part of the roof space. The boundary layer of air adhering to the upperside of the ceiling will never get hot, effectively insulating the ceiling from hotter air above. This seems to apply when the gap between the aluminium foil and the ceiling may be only 50mm or so.

Remember too, that air, as well as being transparent to thermal radiation, cannot itself radiate thermal energy.

Finally, as a builder, I recommended (and fitted) a couple of whirlybirds to clients' roofs many years ago, and got such a bollicking when they didn't work, I stopped and had a bit of a think about it...

Hope this makes sense.

yeah I always wondered whether they worked or not. I know that when you stand next to one spinning you can't feel a breeze which would suggest they arent doing their job. I would think that cross ventilation with movable louvres on gable ends and eave vents would be more effective

Steve,

You're probably right about louvres on gable ends etc being more effective at shifting hot air out of attic spaces, but that's not the point. Or at least that's what I'm trying to say.

You could suck the hot air out of your attic with a "movie set wind machine" if you wanted, but provided you had a reflective radiant barrier under your roof, and it was preferably painted white, it wouldn't make any difference to the temperature of your ceiling, and that's what causes all the grief.

Choice magazine did an article on whirlybirds in 1999.

http://www.choice.com.au/viewArticle.aspx?...tors+(archived)

Probably quicker to Google: "Home roof ventilators" + "Choice" (Australia Search)

BTW, the Australia Building Codes Board has gone ahead and included the whirlybird clause in their 2006 Building Code of Australia.

The say (defensively) they did some modelling and found that roof space ventilation showed some small benefit. Depends on what data you plug into your model I suppose.

You didn't have to "model" this one, BCA. Just take your hand of it, and press your palm up against the ceiling on a hot day.

yeah i just read the article, very interesting. I always thought thata 60degree roof space can't be helping on a hot day. I am still trying to get my head around it but I guess that hot air can't penetrate materials as much as radiant heat.

Steve,

If you paint your roof white and slip in a radiant barrier, you don't have a problem.

The air in the roof space might get to 60°C but not down close to the ceiling. It is highly stratified. Hot air rises.

The manufacturers of whirlybirds rely on our jumping to the wrong conclusions about all that hot air. It's natural to think it's making our house hot.

In 2001 the Queensland Govt built a house at Rockhampton to testbed best pratises in tropical design. It included an elaborate and much lauded roof space ventilation system. Although the actual experiment on roof space ventilation was botched, it was reluctantly conceded that it made little difference to the temperature of the living space. Check it out:

http://www.build.qld.gov.au/research/libra...StudyReport.pdf

I say the experiment was botched because they chose days that were 1 month apart to do the "vent open" versus "vent shut" comparison, which is not good science. By their own admission, meterological conditions were also different. InSOLation is also different from month to month.

They seemed reluctant to run a proper test, which is a real shame, because here we had a fully instrumented structure that could've given us valuable research data and settle the argument.

To the best of my knowledge no whirlybird manufacturer has ever published the results of any "before" and "after" testing, and I think I know why.

On a slightly different note, a friend of mine has an older house which has a higher roof - they were saying back in the days when there was less technology, houses like this were better at staying cooler - because of the larger room space.

I know over summer it can get a little uncozy in our box - so would anyone agree that a house with a higher roof (the space between the floor & the ceiling) be a better option?

We had 2 whirlybirds put in our roof, and vents in our gables. We don’t for one minute think it will make a jot of difference to our household temperature, we have very thick (and expensive) insulation above our ceiling to isolate our house from the heat outside. We put them in because the temp in the roof space was getting too high and we have a gas heating unit installed in the roof space. The delicate electronics (wiring insulation inc‘) in the unit will last longer if the temperature doesn’t get to the outrageous levels it did before we had them installed. We were replacing lighting transformers at a ridiculous rate also before the installation of the whirlybirds .

heaps of things you can do to reduce summer heat gain. Shadeing eastern and westarn windows from the OUTSIDE with trees, external louvres is essential. Also ensuring eaves on northern side arewide enough to shade windows. Isulation is also essential in the walls and ceiling space, and open up the house in the cool of the night and close it up in the day by about 8am or whenever it gets hot. Further and more expensive options include increasing the amount of exposed masonary materials(brick,concrete,tile) on the inside of the house can act as a heat sink, sucking in all the heat, kinda like why a cave is cool. oh yeah and get a whirlybird! ha ha

CP/M User

Saddly, another urban myth. Despite numerous experiments detailed in the literature, there's no evidence that ceiling heights have any bearing on living space temperature

We once had a Queenslander with 3 metre ceilings, and it was a furnace in summer, until I replaced the old silver-frost roof with white colorbond and fitted a radiant barrier.

I feel you need a 2.7 metre ceiling though if you're going to use ceiling fans.

I am in the Architectural industry and have assisted in solving problems for others. Unfortunately I'm unable to solve my own problem. I have read the comments made. My problem is that this house is located under a canopy of very large trees. The 2 rooms immediately under the trees are most effected. The rooms are badly effected by mould and mildew, to such an extent that the walls and ceilings have to be re-painted annually. The walls have been treated prior to painting making no difference.

The roof is pitched/concrete tiled with no apparent break in the tiles. We have considered putting in a couple of 'whirlybirds'. Will this solve the problem or am I wasting my money? Is thare anything else that can be done. Any suggestion will be appreciated.

Mat
0414 899 861

Mat,

Looks like my last attempt to post got eaten by the Diebold !

Re your mould problem: I think whirlybirds could be helpful provided they were ducted through to the living space and not the roofspace which is the usual practice. That assumes that lack of ventilation could be the cause. But would there be enough breeze to drive the rotors under that tree canopy ?

Before I started cutting holes in the roof however I think I'd check the more obvious things first. Can we assume that if you're in the architecture business you've already installed the appropriate insulation for your climate, that your tiles are sarked, preferably with downfacing reflective foil, that you’ve checked for sources of moisture behind the walls ?

If you’ve done all those things and still got a recurring problem then it’s time to go looking for the not-so-obvious, like the link to the micro-climate created by the tree canopy. Is it possible I wonder for the cooler environment under the tree’s envelope to be somehow causing the temperature of the surfaces of your interior walls to be pulled down to the dewpoint ? If the surfaces of the walls can loose heat radiatively to cooler surfaces (“radiation sinks”) either inside the house or outside under the cool canopy, and if the relative humidity inside is high (as it usually is), then you might get the conditions for the growth of mould.

You might have a high spore count too, under the canopy. I’ve noticed some trees (eucalyptus torrelliana for example) seem to get a lot of black mould on their leaves.

If the walls are, say, gypsum, could they be losing heat to a cooler cavity, or a backing wall that may be acting as a radiant heat sink ?

Final (and desperate) suggestion: increase the natural light levels in the affected room. Make use of some of that excess UV that’s floating around under the hole in the ozone layer !

Having done a lot of construction industy work alongside a mate that is a licenced plumber(water+ roof) we got to talking about w/birds effectiveness one day as we took a roof sheet from a double story building so as to gain access,the blast of hot air as we removed the sheet of iron was intense to say the least as i was on the ridgeline i was the recipient of the heat blast and this exercise ended up with his tale of how he had a contract to install numerous w/birds of the largest size on a huge warehouse in Brisbane.The w/house was used for hundreds (yes hundreds) of insulated coolroom containers...The roof of the containers was approx 6 feet under the w/house roof and the base holes cut into the roof were from memory a metre across so the w/birds were large of course...bottom line was the electricity power bill after the w/birds were installed for the w/house was REDUCED by some enormous percentage due to the effectiveness of the w/birds,and the reduction in power used by each container...i dont remember the reduction % but from memory it was really significant and definately announced the project as most worthwhile..

My own w/bird has a poly horse feed bag taped over it during winter...they do work and they work well,one only has to place their hand over a unit on a warm day and feel the heat that they do extract,damp places improve with the into of a w/bird to the roof also. I believe they are of utmost importance in conjunction with decent ceiling insulation.

gryphon

The situation you described is not remotely similar to that of a normal domestic residence.

The whirlybirds you helped install removed the waste heat from the condensers (on the refrigeration units on the containers) thus reducing the head pressure on the compressors, thus reducing the current draw. No surprises here. You can easily double your own electricity bill by not allowing the heat from your domestic refrigerator's condenser to escape. It would be good for the environment if whirlybirds were ducted through to a ventillation grill in the ceiling of the kitchen right above the refrigerator to help cool the condenser.

As I explained earlier however, removing the hot air from the attic space above the ceiling in a house (regardless of how you do it) cannot reduce the temperature (to any meaningful extent) of the living space.

I have no doubt that you will feel a lot of hot air being drawn out of your wihirlybird on a warm day (as you described). The air in your attic space can easily reach 60°C. But that hot air has almost no effect on the temperature of your ceiling. I know this is a difficult concept to grasp, and plenty of building professionals, as well as the new breed of energy consultants, find it confusing. Manufacturers of whirlybirds like it this way, and add to the confusion by promoting ambiguous claims.

I'm renovating at the moment, and trying to find the simplest method of cooling the house (in Melbourne). We got some trade literature from someone selling whirlybirds, and I was passing that through my internal bulls**t detector becuase it didn't sound right. So I researched it a bit.

It appears that whirlygigs don't work by emptying hot air from the roof cavity that may otherwise radiate through the cieling into the living spaces beneath. Nor do they work by catching a breeze and bringing in cool air. They are supposed to set up a convection column in the house, a bit like a well-functioning chimney.

It goes like this. Bang a hole in your roof and install a whirlygig. Then, bang a hole in your cieling and place a closable-duct. Finally, bang a hole in the timber floor (or open a window that's down low). When air in the living room warms up, it rises into the roof cavity and out the whirlygig. This creates a suction that brings in cool air from under the house. When it's winter, close the duct so prevent the convection column from operating.

The important thing is to make sure that the incoming air is cool, so keep the inlet area damp and shady. But in Melbourne, when it's 38C outside, there is no cool air to bring in, so it probably won't bring much joy.

The whole thing may not work well if you have a tiled roof, which naturally has lots of cracks that leak hot air. And it's also really important to have roofing insulation so that you can keep heat in in winter.

I'm not yet convinced that the theory above actually works - it may depend on tile roof versus sheet iron roof. But I am convinced that whirlybirds will remove moisture from roof cavities that may rot the structural timber, especially if the bathroom fan is extracting moisture into the roof.

Some of the 'Green' commercial buildings that win awards these days also cool themselves using convection currents. You just have to translate the principle into domestic buildings, and whirlybirds may play a part in that.

Today is the first time I've seen this forum, but I'm hoping someone can give me some sensible advice instead of the marketing I've received so far.

I live in Melbourne in a 3-storey town house which faces east/west. There are no doors between the ground floor and the top floor, where the master bedroom is so all the heat travels up from the lower floors to the top. There is no roof cavity and the roofing is dark grey tiles. We have a wall-mounted A/C installed in the top floor but it was wrongly put above the stairs, so all the cool air flows down the stairs (I am in the process of tracking down an A/C technician to look at relocating the A/C to a more sensible location). All the windows have awnings and/or drapes.

I am considering installing a whirlybird which drags air straight from the highest part of the ceiling in the top floor. I would put in a vent in the ceiling which can be closed in winter.

What to people think?

Palmy,

Sound like the house I used to rent. My bedroom copped the western sun. No fan, no air con.

Whirlybirds are essentially a vent that moves hot air up and out. They perform the same function as a pipe with a witches hat on top. They exploit the fact that people think that things that move are doing something, but things that stay still don't do anything.

Think of your house as a chimney or column of air. Hot air will rise within it. If you open the top of the chimney with the bottom closed, not much will happen. If you open the bottom of the chimney with the top closed, not much will happen. But if the top and the bottom of the chimney are both open at the same time, then you will get an updraft through the chimney.

Hot air may come from electrical devices such as refrigerators, computers, toasters, hot water systems, ovens etc. or your body heat. Make sure that you have pelmets over the curtains to stop air cycling past the window and spreading warm air around.

Prevent hot air from forming, and get rid of it once it has been formed. If you remove the hot air from your master bedroom with a vent in the roof, then air will have to be sucked into the room from elsewhere. But remember, the incoming air may be just as hot as the stuff that was vented.

If it was me, I'd move the air con into the bedroom.