The living room and kitchen in my house share a cathedral ceiling (the rest of the house has standard ceilings). The room gets really hot in summer as there is no ceiling space to create an air gap and presumably no insulation between roof sheets (metal) and the ceiling sheets (fibre-cement sheet).
Does anyone know of solutions for ventilating such a roof so the hot air is automatically extracted? Can whirlybird type devices be installed in this sort of application?
Skylights have been suggested, but those to be opened and closed manually and I want the room to be self-tending.
Kill two birds with one stone. rondo under the rafters and re-sheet. Plenty of space for some decent insulation with the bonus of hiding the ugly rafters (my opinion). We do it for plenty of people, will make the room much more modern looking. More expensive than a whirlybird though.
I take it you are in to minimalism?? Or did you remove your board racks for the photo??
Select to expand quotePugwash said..
I take it you are in to minimalism?? Or did you remove your board racks for the photo??
Minimalism all the way. Sorry the place is so untidy in the photo.
So, there has to be perlins on top of the rafters to fix the roof to. May only be 5cm thick though, but that should be enough to get a decent air flow. I think an extractor/whirlybird at the apex would help, but don't expect a huge difference.
What colour is the roof? Anything dark is going to make it hotter than something light.
I wonder what it would cost to put thicker perlins in, so that there's room for some decent insulation.
(I like exposed rafters, so changing the ceiling would be my last option)
I like the beams too, though I will repaint all white this winter.
Roof is steel with dark dark red rock coat stuff on it. ie HOT!
Yes repaint and rip down the ugly lights lol
Ok, if rafters are staying it might be worth checking if there is insulation under the coro, if not, remove coro, roll out blanket insu, re place coro.
Then above the hallway door, put in an exhurst fan as high up as you can, duct it to a whirly bird or better still 12v fan to drag the hot air to the out side.
With your ceiling fan on the air movement will make the room better.
Select to expand quoteImax1 said..
Whats with the bars on the window ? I think the couch is safe ! 
They are to keep him in, not other people out.
The tin battern on top of the rafters will be about 35-38 mm thick and running the opposite way to rafters and spaced at 1200mm so a whirly bird will only clear the hot air from in between the battern and not the whole roof. The problem with pitched exposed ceilings is they get hot. You need to create a void, as mentioned battern the underside of the rafters and gyrock with insulation. If you want to keep the exposed look you can build a ceiling in between and the roof rafters , insulate and gyprock leaving around 50 mm of the rafters exposed . There's no cheap fix.
Other option .. big air con
anyway to be serious I agree with Mclovin - but to do a ceiling in there yourself would be a piece of cake as we have seen you are handy by other posts here.
It's an optical illusion ,
If u stare at the couch long enough it seems like the walls are moving.
install a solar powered extraction fan at the high point of the space . will only work when sunny .....that will work .
McLovin is on the money.
These types of ceilings are crap at insulating, and (as said before) with a 35 odd mm gap between the tin and the gyprock, it is hard to put in any meaningful insulation.
The best insulation you can get is an extruded polystyrene, which at about 40mm thick will give about R1.5- which is still way below what should be in a roof space. It is times more expensive than glasswool insulation, and you'd need to take the roof sheet off to do it.
Even if you were to get good airflow past the underside of the ceiling lining, there would still be heaps of radiant heat coming down from there on a hot day (like the way the sun can make you feel warm when the air temp is cool).
If there is no gap between the batten and ceiling lining (most likely the case) the level of ventilation between the batten and ribs of the tin doesn't help a lot- and the radiant heat would be the big issue anyway.
Do the McLovin thing and put in a R4 or greater batt, which should fit in the depth of the rafter.
Clarence
Select to expand quoteImax1 said..
It's an optical illusion ,
If u stare at the couch long enough it seems like the walls are moving.
Number of beers this evening Imax?
Select to expand quoteclarence said..Imax1 said..
It's an optical illusion ,
If u stare at the couch long enough it seems like the walls are moving.
Number of beers this evening Imax?
None !
And I don't even own a bong ,
Im natural this way 
Made u look back at the photo though , didn't I ?
Select to expand quoteImax1 said..clarence said..Imax1 said..
It's an optical illusion ,
If u stare at the couch long enough it seems like the walls are moving.
Number of beers this evening Imax?
None !
And I don't even own a bong ,
Always bludging, huh?
Select to expand quoteBuster fin said..Imax1 said..clarence said..Imax1 said..
It's an optical illusion ,
If u stare at the couch long enough it seems like the walls are moving.
Number of beers this evening Imax?
None !
And I don't even own a bong ,
Always bludging, huh?
Bludge , that's one thing I never do .
Cant I just be happy ?
Much food for thought here. And, yes a new ceiling between the rafters would be a pretty straightforward job to do over the winter and not too spendy either. 
I reckon you are over thinking it. Paint the outside of the steel house roof off white. Surfmist colour is a common Colorbond roof colour. In your situation it will make a huge difference to the internal ambient temperature
If you do follow the above advice, be aware of the risk of creating a condensation trap between the new ceiling and old ceiling.
I would comment, but the way it works in Qld is completely different to southern Australia (in Qld condensation comes from external moisture hitting air conditioned air inside the building generally).
Clarence
Cross flow, wave and ridge, int or exterior, velux or roto roof windows, mechanical or electrical openings, also auto atmospheric open closing
Throw some shade cloth over your house. Choose a nice camo green and it will stop THEM from finding you.
So uncluttered I like uncluttered...my roof same same like this one rafters everything same same I luv em who would want a more "modern" look...wake up doors open front back when hot hot fan goes on sometimes
Classic problem of raked ceilings.
Assuming insulation is your major problem and if you don't mind spending, the best option is rip the whole roofing material, battens and insulation off and put on pre-fabricated insulated sandwich panels and motorised operable skylights to expel hot air from the space. If you have a clerestory to the right of shot, you can put bottom hung windows in to expel air that way. Also check your wall insulation is adequate.
In any case, R4.8 insulating panels should do the heavy lifting and no need to ventilate the roof. They even come with flat white Colorbond underside if you want to rip the ceiling out too. They can go straight over the rafters. No need for purlins or a separate vapour barrier. Very fast to install too.
Many manufacturers but these guys bondor.com.au/products/insulroof%C2%AE-next-gen-corro-roof?refid=2 and Kingspan are market leaders.
That'll be a case of coldies thanks.
Did this in a pool area, 100mm polystyrene slabs glued between the rafters. Clean up the gaps with quad , then paint. Looked very clean, reduced the noise and improved the thermal.
The insulated sheets suggestion is good but installing the sheets straight over the rafters isn't. You'll need to retain the battens. Also it's a house not a stand alone roof so the chances are very high that the insulated sheets will have to somehow marry up with the existing roof, the hips, the valleys, ridges and the existing gutters. And somehow look neat and not leak during rain.
I'd paint outside of house roof a white colour first. Then consider options for insulation 2nd.
You're proposing installing the insulated sheets in the same direction as the rafters! With the sheet joins unsupported and running parallel to the rafters. That scenario isn't covered in the company data sheet.
