Roof Ventilation

[Ausfree]

Because of the extreme hot weather we have been having, I have been thinking about installing roof ventilation to remove the hot air build up in the roof.:)

I have looked at those whirly gig thingo's that depend on wind power to remove the hot air and two things worry me about them....:confused:

1) they look unpleasant and are very bulky.
2) If there is no wind they lose their efficiency.

I see Masters hardware have a Solar Powered one on sale!!:)

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Any body with experience have any thoughts on these.

I think the hotter it gets,the harder they work. However, are they noisy and are they effective?????:)

[superquag]

Don't know about the Solar powered ones, IMHO they need to be big, say dozens of watts to make any real differance...
Whichever way you go, it is vital to have plenty of vents etc for outside air to get INTO the roof void... to replace the super-hot stuff you're extracting.

Indeed, you can't have too much, except in winter when you want to be storing the heat...

Have a look at prevailing breezes and utilise the wind to blow IN as well as suck out.

If you have evaporative A/C, then you may use a manhole or room ceiling vents as your flow-thru. We have a 1m x 1m manhole.... works well. :D

[Andwoo]

As a plumber Iv'e installed a few of those and think they are pretty good. I think they spin not because of the wind but from the thermal movement of hot air rising.. so I wouldn't worry bout them not working on a still day. I've never hard them making any noise at all when installed correctly. I've also been told they are good in winter as they prevent moisture from building up. I intent on putting a few on my own roof, don't think I'd bother with solar powered vents though.. seems like a gimmick to me.

What type of roof do you have? is it tiles or tin? Tiles are pretty good for ventialion as there are lots of gaps between each tile. If you have tin I think you'll notice a fair difference by adding ventilation as a tin roof seals up quite well.

[Rimmer]

Andy, (Andwoo) is right on the money!

[Stuck]

Superquag's pretty much on the money. Those "whirlybirds" will work as long as you have an entrance for air at a lower point such as your eaves. I've fitted them to industrial buildings during construction and I know how far and fast hot air will travel to get out (welding fumes from inside are a dead giveaway) when you cut that first hole :eek2:.

Cheers,
Anthony.

[mike_ie]

I used to earn my keep in SA crawling round in other peoples attic spaces running cables from one end of the house to the other - to say the difference between roofs with whirlygigs and those without is an understatement. On a summers day it was easily a difference of ten or more degrees, so I reckon they do work, and well.

I also fitted two of the standard whirligigs into the roof of my ex's parents shed - put them almost at the apex of the roof, a few feet in from each end. The temperature difference was definitely noticeable immediately after they were installed.

[land864]

Andwoo

What are you dwiving awound in :)

I'll keep an eye out for you in the land of Nuts and Berries:eek: ( As our inner city so called friends call Nillumbik :) )

[Ausfree]

As a plumber Iv'e installed a few of those and think they are pretty good. I think they spin not because of the wind but from the thermal movement of hot air rising.. so I wouldn't worry bout them not working on a still day. I've never hard them making any noise at all when installed correctly. I've also been told they are good in winter as they prevent moisture from building up. I intent on putting a few on my own roof, don't think I'd bother with solar powered vents though.. seems like a gimmick to me.

What type of roof do you have? is it tiles or tin? Tiles are pretty good for ventialion as there are lots of gaps between each tile. If you have tin I think you'll notice a fair difference by adding ventilation as a tin roof seals up quite well.

It's cement tile, mate.:D Thanks everybody for your input.!!:D:D

[Andwoo]

Yer mate same as me, I think they breath abit so you'll have plenty of cool air flowing in while the whirlybird does it's thing
.G'day land864! I'm usually in my mazda bt-50, looks the same as every other white ute! I often cruise around in willy my series 3 when i can.. if you see him about give us a toot

cheers, Andy

[101RRS]

Testing has shown that there is no difference in temps inside the house but roof temps are reduced - not sure why but that was the finding.

Having said that, I have two large ones on my roof and they also have a fan attached to the whirly turbine at the top - they work by creating a low pressure spot that suck the hot air out. Also they provide a hole in the roof for hot air to escape. Mine are dead quiet and I have never seen them stop - even on a what seems to be a completely still pre dawn morning.

Garry

[superquag]

Testing has shown that there is no difference in temps inside the house but roof temps are reduced - not sure why but that was the finding....

Garry

Yep, may well be... during the testing, but insulation is in the roof void, and if the air temp is 50+ degrees.... then some heat will permeate through...and be stored in the inter-fibre spaces... to be released through the ceiling plaster some time later.
Have a string of hot days... and you swelter inside at night when its noticably cooler outside. - First thing I noticed when we extended the insulation throughout the whole house...

Ausfree, cement tiles are a machine-manufactured item and therefore will be of uniform size and shape... which means they seal a lot better than kiln-fired clay tiles... which are less regular.

You could always slide back a few tiles - apex and lower down - and see what a differance it makes...

[clubagreenie]

We had one and while it moved didn't seem to make a difference. Then had the roof cleanded and repointed and fitted another (& moved the original) . Fitted at each end of the long axis of the roof ridge, as high as they could fit. Then fitted eave vents also along the long sides (four each side). That made the difference, it cross vents if there's a breeze from the east or west but if it's still they'll still spin away drawing from the eaves.

[Piddler]

HI, 2 experiences.

I have 2 on my shed which is 15m x 8m I found welding on a summer day to hot. I put in 1 and was so pleased put in a second.

We also have put 2 on our house. We have a colorbond roof an a 3 year old house. We found in the winter they are sealed up so well when we had a few weeks of cold days with no wind condensation laying on top of the silver paper under the roof.

We got our builder to put them in and checked 4 weeks later no moisture at all. We also think the house is a little bit cooler in the summer by getting rid of all that hot air.

Our builder said he is going to put them in all his builds if they let him as there is a lot of new brick and colorbond houses with moisture issues as they are so sealed up with no air movement.

Very happy with them here. :)

Cheers

[yt110]

I have 2 on my house and 2 on my shed they are great.
I have heard that in bushfire prone areas the under eave vents cound draw embers into the roof cavity so I dont have them.
The spinners with the plastic bearing support arms are quieter than the ones with the steel or aluminium ones
Jim

[superquag]

I have 2 on my house and 2 on my shed they are great.
I have heard that in bushfire prone areas the under eave vents cound draw embers into the roof cavity so I dont have them.
The spinners with the plastic bearing support arms are quieter than the ones with the steel or aluminium ones
Jim

Thanks for that, something I'd not considered, as we're not in an obviously risky area.

Having said that, - and very open to correction here - perhaps a steel mesh ("flywire") over the ventilation holes. Not only, but a metal frame as well, as many of the hole-fillers/fittings are moulded plastic frame & grilles.

Using a fine mesh would restrict air-flow, but adding another one or two would solve that.

[loanrangie]

Testing has shown that there is no difference in temps inside the house but roof temps are reduced - not sure why but that was the finding.

Having said that, I have two large ones on my roof and they also have a fan attached to the whirly turbine at the top - they work by creating a low pressure spot that suck the hot air out. Also they provide a hole in the roof for hot air to escape. Mine are dead quiet and I have never seen them stop - even on a what seems to be a completely still pre dawn morning.

Garry

They may not remove heat from the house but as we have evap cooling the heat in the roof cavity heats the ducting which reduces the efficiency.

I have been meaning to add a couple on our roof but without somewhere for air to be drawn in (eves closed in ) i'd need to address that first by fitting vents.

[Ausfree]

Fitting vents is a good idea, I have taken that on board as when you think about it a roof ventilation system does need to draw cool air from somewhere to replace the hot air extracted from the roof cavity.

I do notice, as our house is a modern brick veneer on concrete slab type, so the water pipes are through the roof cavity. So, on a hot day when you turn a cold water tap on, the water that comes out for 30 seconds or so is piping hot. On real hot days you could make a cup of coffee with water straight out of the "cold" water tap. I can only imagine how hot it is in the roof cavity!!

Another question??.......with the solar powered roof ventilators, wouldn't they work harder the hotter it gets??

Thanks again everybody for all the inputs, I am much wiser now!!:D:D

[101RRS]

They may not remove heat from the house but as we have evap cooling the heat in the roof cavity heats the ducting which reduces the efficiency.

I have evap cooling as well - now that really clears the heat out of the house even with the water turned off.

Garry

[superquag]

Our well ventilated roof space can top 50 C. - Opening the 'junkroom' door (where the 1m - square manhole lives) and running evap A/c flat out will drop 10 to 15 degrees off that.

Solar cells operate by "light" not by heat. Indeed, they really don't like HOT at all and reduce their output (for the same light intensity). Our rooftop panels give their best when the temperature is lower... A hot day will see them derate themselves around 15%. An equally bright winter's day is MUCH better.:cool:

How much that affects a 'solar Vent' is beyond me.