How do whirly birds on roofs work?

[qld]

What stops the water getting in?

[petersemple]

I have no idea, but there are two on our roof and water doesn't get in. I guess it's the shape of the vents, because there's nothing particularly tricky about them.

Peter

[rod1949]

Magicness. God knows but it dosen't. I got one on me shed and not a skeric of water gets in no matter how hard it is raining.

[BobL]

When there is no wind the rain falls vertically and there are no vertical openings exposed. When the bird spins it creates an air stream that goes out of or away from the bird so this is enough to deflect the air drops away. The faster the wind speed the more the rain angles into the openings but the greater the air speed of the air coming out of the bird is enough to deflect the rain drops.

[qld]

Is there anything in the whirlybird mechanism inside the roof.

Like the outside part you can see is just a lever to propel a fan that hangs inside the roof adn cant be seen?

Or is pretty much everything you can see from the outside is what is in the mechanism of the whirly bird?

[petersemple]

On ours, the only thing inside is a small support structure and bearing assembly. What you see on the outside is pretty much it.

Peter

[qld]

Do all whirly birds blow outwards not inwards?

ive heard you get one whirlybird installed at the highest point of the roof and one at a lower point and one of them spins a different way.

[Groggy]

Many people look at the vents and think they will leak during a rainstorm. The wind that almost always accompanies a rain shower or storm actually causes the turbine to spin and blow rain drops away from the vent.

I believe the angle of entry for the rain means that any that does get inside hits the inside skin of the vent, then runs down until it exits the cap section. The water always remains outside the vent tube.

[BobL]

Do all whirly birds blow outwards not inwards?

ive heard you get one whirlybird installed at the highest point of the roof and one at a lower point and one of them spins a different way.

This can happen when there is no wind (or the low bird is in a dead air zone on a roof, and hot air rises inside a ceiling cavity drawing cooler air in at the bottom. Once the external air speed picks the bird will turn with the wind.

This is a silly way to vent. A better way to vent a ceiling cavity is to place all birds up high and just have passive waterproof vents down low.

[Sparhawk]

I've only seen them spin one way. What the suggest is to put vents in your eves to allow the air to flow in and circulate.

[Groggy]

This is a silly way to vent. A better way to vent a ceiling cavity is to place all birds up high and just have passive waterproof vents down low.

Yes. If installing these yourself it is important to also install the eave vents to provide the airflow through the roof. I need to put a few more in my house as on a hot day I can hear the air moving through the vents.

[Skew ChiDAMN!!]

Do all whirly birds blow outwards not inwards?

ive heard you get one whirlybird installed at the highest point of the roof and one at a lower point and one of them spins a different way.

They're designed to vent outwards. The best method is to put a whirlybird up high and inlet vents underneath the eaves.

With modern eaveless suburban houses [ugh! Dog boxes!] this isn't possible. I have seen a recent trend for a second whirly lower down, but this should really only be a last resort; there are other options.

I'd say it's more often done by people who don't think the job through or want to do it on the cheap. Cowboys.

[rod1949]

Another option if you are looking for roof ventilation is the E-vent from this mob http://www.combinedmetalind.com.au/index.htm There may be similar in your neck of the woods.

I actually have 2 E-vents on the roof ridge and vents in the eaves around my house.

[murray44]

I have also seen a vent that looks like a combined skylight and vent, the roof fitting looks like a normal roof tile but it's made of perspex and 'appears' to have a vent also. I only saw it from a distance, I could be wrong..

[Fuzzie]

I've also heard anecdotally that during Cyclone Larry in Innisfail a lot of these things got sucked off roofs and resulted in a lot of interior water damage that would not otherwise have occurred.

I guess the typical wind loadings that suck roofs off houses also cause big enough vacuum effects to suck enough air out of the house through the roof vent to dislodge the whirlybird.