Removing hot air from a cathedral ceiling « Alternative Technology Assn Forums

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Removing hot air from a cathedral ceiling

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Started 11 years ago by MelbourneStevo
Latest reply from Bushwalker

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MelbourneStevo
Member

A poorly designed cathedral ceiling traps hot air in our second story bedroom during the summer.

One alternative is to add something like Edmonds Cathedral Ceiling Vent system:
http://www.edmonds.com.au/html/products/cathedral_ceiling_ventilation_kit_250mm.htm

Its not a terrifically attractive internal vent, but there don't appear to be alternatives. A roof window, while maybe more attractive is much more expensive and I'm concerned about the thermal properties.

Any alternative suggestions will be much appreciated.

Posted Thursday 5 Nov 2009 @ 10:30:25 pm from IP #
ghostgum
Member

Our raked ceiling has a skillion roof. We have some high windows on the south side, which let in light reflected off the adjacent roof, and are openable. You can't leave them open if there is any chance of rain.

Can you use an adjacent stairwell as a chimney with a high window?

Posted Thursday 5 Nov 2009 @ 10:55:14 pm from IP #
sun2steam
Member

I am working on something which might be unrelated - but only at first sight.

I will install an evacuated tube collector (large diameter manifold, no heatpipes) on my roof for space heating by hot air in wintertime. And I always wondered what to do with the heat energy during summer.

And here I get back into the loop: How about adding a short pipe as chimney on top of the collector. The other end of the collector would be connected to the top of the room. The updraught will suck air for the room whenever the sun shines. This should be more reliable than a whirly bird which will not work when there is no wind. But that is actually the time when ventilation is needed most.

Posted Friday 6 Nov 2009 @ 3:25:48 am from IP #
ghostgum
Member

On a recent trip to Central Australia I saw a great use for a whirly bird. It was mounted on a pit toilet and was being used to suck air up a flue to prevent the toilet smells. Other methods were black painted flues on the north side causing a convection flow, and a solar panel driving a 120mm fan.

Getting rid of excess heat under a cathedral ceiling has some similarities. However you also want to avoid heat loss in winter. So a fan solution would also need a butterfly valve or similar.

Posted Friday 6 Nov 2009 @ 5:29:47 am from IP #
JohnB
Member

Cathedral ceilings are easy to do well and also easy to make hopeless. Sounds like you have the latter.
You don't mention if it is a flush ceiling (lining below the rafters) or and exposed rafter ceiling (lining above the rafters).

Typically exposed rafter ceilings have relatively poor performance, because unless the designer or builder have used particularly deep roofing battens, the insulation is squashed into a tiny space ie roof batten depth.

For example, I'm currently working on a cool climate project, and the composite timber I-beam rafters in the two cathedral ceiling areas are 300mm deep - to fit the 260mm thick R6 insulation and still allow an air gap below the reflective sarking.

If you have a flush ceiling and the performance is poor, there is probably just not enough insulation in there - difficult and expensive to remedy.

The add on vent you linked to would work alright, but it's sort of addressing the wrong end of the problem. You really want to get the heat out of the small roofspace void so that it doesn't heat the room up, rather than let the room get hot and then drain it.

I have seen one concept by a chap in Victoria that involved leaving a gap in the sarking right along the ridgeline, and using a vented ridge cap - I guess he'd never heard of AS 3959-1999 Building in Bushfire Prone Areas - not a very safe idea and certainly not something I'd risk doing.

Unless someone REALLY wants their ceiling to go to a point (often VERY high), I always put a flat ceiling at 2700 or 3000mm (or to suit) in a loft roof so that a simple triangular roof void is formed at the top. This way the small spaces between all of the rafters have somewhere to 'drain' hot air up to and it's easily vented out the ends with normal gable end vents. Of course, you need the lower ends of the rafters to finish in eaves so you have somewhere for ambient air to get into the spaces to start with. This sort of fix is expensive, but with better insulation on the flat ceiling area it will improve Winter performance as well.

Another option instead of the central roof vent could be a pair of small wind-out awning windows, mounted high up in the wall each end. In Winter just cover them with a shutter which is a neat fit into the reveal.

It's hard to know without more information. You could post a photo onto the ATA Facebook page, so we can see the issues.

Posted Saturday 7 Nov 2009 @ 3:52:26 am from IP #
MelbourneStevo
Member

Thanks all - I appreciate your input.

John B - its a flush ceiling over a 2-storey void, and its over 10-metres from floor to the highest point. I've suspected for a while that we might have been dudded on the insulation.

Awning windows high in the walls is definitely something to consider.

Posted Thursday 19 Nov 2009 @ 3:56:42 am from IP #
knobblysnail1
Member

I also have a hot Cathedral Ceiling

JohnB - You indicate that the first step is to get the heat out of the small roofspace void. Do you think an active system like the SmartBreeze (www.smartbreeze.com.au) solar powered fan would be effective? It is supposed expel air from between the corrugated iron and the sarking during the day. (As I am not in a bushfire zone I guess AS 3959-1999 wouldn't be a concern for me.)
At night it is supposed to work in reverse - pushing outside air in via the same space. This seems somewhat counter-intuitive to me - I thought I would want to expel hot air from inside, or at least draw in cool external air directly - not from under the roof.

ghostgum - are you aware of any extraction fans with butterfly valves which are weatherproof? My gable is South facing without eaves.

Posted Thursday 19 Nov 2009 @ 12:38:49 pm from IP #
JohnB
Member

MelbourneStevo,
Your 10m tall ceiling peak is interesting, assuming your upper floor is at a relatively 'normal' height the ceiling must still be very tall over upstairs. Anything that will 'drain' the upper air will help if you can't stop the heat from getting thru the structure in the first place - in that regard your originally suggested fan unit would probably be cost effective - because 'fixing' the building itself would be a lot more complex.
With a flush ceiling you're probably right that there just isn't enough insulation in there. In Summer, external roof colour will have more effect above a raked ceiling than it will above a normal vented/ventable roofspace, purely because of the smaller volume of air to be heated before the insulation gets overloaded.

Knobblysnail1,
I had a look at the website you linked, the animated graphics make a reasonable case for Summer ventilation, but I agree with your assessment on some of the other 'functions'. My concern would be how much of the roof surface area the unit would actually draw air from. The graphics conveniently show a nice deep airspace, when in reality the airspace under the ribs of a Colorbond roof is approximately 16mm deep where they cross a batten. I can imagine the unit effectively cooling the sheets in line with the actual unit, as well as drawing air from 'along' the batten space either side. Of course it all helps, but it depends how many of the units you need to make a real difference.

Posted Thursday 19 Nov 2009 @ 10:20:54 pm from IP #
kate
Member

can't get any advice not aligned with companies selling products.

I have an old 80s 2 story townhouse, hot in summer cold in winter, with cathedral ceilings, exposed beams, extending to eaves but gaps between rafters to outside bricked in. Hot in summer. a builder is coming to gyprock my brick walls and ceilings, to keep out dirt and insects from ceiling. cement tiled roof on battens, seems to have old foil insulation under battens, then exposed ply boards on top of rafters. it is very hard to find good info to do the right thing with making it more energy efficient. i have asked builer to put insulation in between rafters before attaching by cross battens a cheap gyprock ceiling.

what do i look for in insulation. any problems from stopping air flow to rafters by insulating. should i leave a gap or fill with insulation. very hot upstairs. airflow limited by having to close windows on windy south side due to rain - no eaves on that side. I can open windows only on top story eaves covered west side while out or during heavy rain(when it is very hot and steamy). I want to vent air out the top with minimum cost and minimum alteration to body corporate roof.cross breeze not very achievable due to walls etc.

could build small attic ceiling but no air flow from eaves through rafters, plus ill be closing the gap between rafters with insulation.

is a closable non motorised vent at top of roof or hybrid okaky. it can be quite cool downstairs, cement slab, but humid and close on on still days.

very grateful for any advice.

second issue. open patio upstairs was enclosed . it is too hot to use but keeps heat and rain out of upstairs bedroom.and useful for kids sleepovers etc . i am replacing rotten roof. builder says colourbond with foil insulation. would ritek be better? have no eaves so hard to leave windows open. ritek could extend out further over windows but i would lose the guttering. also exposed rafters in the sunroom but very low ceiling with little air flow. huge heat build up in summer mornings. hate noisy whirly birds. are the new solar star vents any good.do they run all the time. should i also close in exposed rafters with insulation? could i just use a passive maestro-i like these. or an openable skylight to let hot air out. can i cut through a ritek roof for an air vent.

very grateful for help,do not know where else to ask, cannot afford a designer.

Posted Sunday 7 Nov 2010 @ 12:28:16 am from IP #
Buzzman
Member

kate
there's a lot of issues you've raised there and it would be helpful to see some photos of the house, especially the problem areas.

Can you take photos with digital camera and upload to photobucket or similar site and post url here to view pics?

Even without them, I'd say you're suffering from the pre-compulsory-insulation period of piss-poor brick-veneer construction - although I'm curious about that as you sauy the builder is coming to put gyprock over the bricks??? Does this mean you have double brick walls and are contemplating gyprocking over them or what???

Ritek is not cheap, and based on their published R-values, you'd need a celiling/roof panel of 140mm thick to get a decent R-value for the upstairs enclosed patio. This gives apparent R-value of R3.4.

I would not put a ventilator through it as it will weaken the panel and create a brak in the insulation.

As you say it's a villa, and you mentioned body corporate, I presume this preculdes any modifications to the outside walls?

Generally with brick veneer wals exposed to the sun, especially west-facing walls, it is better to put an insulated false wall on the OUTside, rather than a false wall of gyprock on the inside. And Ritek panels might be good for this, as you would only need to batten the wall with treated pine 75X50 battens and fix the Ritek panels directly to the battens. 100mm Ritek is about R2.5.

This creates both reflective barrier, insulation and an air gap, so would be a good solution, and being "architectural" panels, might fly past the body corporate, but the BC would 'own' them once installed, so they would want to be sure of some objective life span for the false wall structure.

You would use Colorbond steel angle flashings to existing window reveals, so you would effectively have an additional 150mm deep reveal on the outside, thus making some eave shade at windows as well.

Weatherproofing the top of the panels is similar, just with wider angle or barge flashings. Quite simple really.

Powered roof vents are the only real solution, as the non-powered ones are relatively ineffective. People on other threads have discussed this and the consensus seems to be the fans need to be able to replace the entire volume of air that has to be removed from the space, so may need more than one, and the cfm (flow rate) is the important value. There are solar-powered whirlybird type vents that might do the job there.

Openable skylights are also an option, and a couple of small opening skylights as close as possible to the ridgeline would be of great assistance in creating a purging airflow. Being unpowered they'd rely totally on convective flows, but this could be assisted with the aid of a large, powerful portable fan.

Posted Sunday 7 Nov 2010 @ 4:11:44 am from IP #
GBD
Member

Melbourne Stevo

If you want to vent the air properly then a condor kinetic is good choice.
It's not an off the shelf item so you'll need to provide a good amount of detail to have the correct size device made for for your home - which combined with a close-able vent/register will ensure you don't loose lots of winter warmth.

Posted Sunday 7 Nov 2010 @ 7:02:15 am from IP #
Etherealise
Member

I know this is an old thread but I thought rather than start another one I'd post here...

We also have a cathedral ceiling that I strongly suspect fits into the 'hopeless' category, and overheating is a real problem. The roof pitch is about 15 deg and slopes down to the north. John B, by "exposed rafter ceiling (lining above the rafters)" I assume you mean that from inside the house the rafters are visible? This is what we have.

From on the roof I pulled off a roof tile and I can see there are pink batts crammed in between the battens, with foil on top. I haven't taken measurements but I think the depth of the whole space the insulation sits in is only about 120mm deep, max. In other words all there is between the insulation and the room below (large open plan living area) is some plastic and thin pine lining. No air gap. The tiles (terracotta) sit right on top of the insulation.

A big problem is that the top of said cathedral ceiling forms part of the roof of built in robes in the bedroom above (!) (it's a split roof design). The cupboards seem to radiate heat into the bedroom from the roof, not helped by some gaps in insulation.

The bedroom, as with the whole house, is double brick, and there is enough of a problem with heat rising through the inside of the house into upstairs where it is stored in the mass, something we are addressing with shading as much as we can. It's great in winter but a nightmare in summer.

Presumably there is no way to vent out air out of the tiny roof space, given it is filled with insulation, so the problem becomes more about venting out heat from inside the room (once everything is done to try and minimise heat gain to begin with)? Or is it possible still to vent out heat from within the insulation packed space at the highest point of the roof?

Posted Thursday 16 Jan 2014 @ 6:57:11 am from IP #
Benny
Member

If that cathedral ceiling is such a problem why keep it? Fit another ceiling below the rafters and stack more insulation in there ?

Posted Thursday 16 Jan 2014 @ 1:50:45 pm from IP #
Etherealise
Member

Well for one thing the roof beams are not straight so it would be impossible to put up a plaster ceiling that would look half decent, and the expense would be huge given it is a large open plan area.

Posted Thursday 16 Jan 2014 @ 2:33:09 pm from IP #
Benny
Member

Sorry - but you said it "overheating is a real problem", so I thought you'd be willing to spend something to fix it properly. Even if you can vent the air from that space there will still be a lot of radiant/conducted heat getting through. I was at a similar property the other day and with the outside air at 25C the internal ceiling was 42C.
Have you even priced a gyprock ceiling - its not hard to install and can even be DIY. They can also fit a secondary set of battens across the beams if they aren't flat to create a much better flat surface to fix the gyprock too.
Also what colour are the tiles ? Worth painting white ? Although I suspect that would be even more expensive than a new ceiling + insulation.

Posted Friday 17 Jan 2014 @ 12:30:40 am from IP #
dave lawrence
Member

Well for one thing the roof beams are not straight so it would be impossible to put up a plaster ceiling that would look half decent,

incorrect ,it is easy to rectify this .as benny said above .battens fixed to underside of rafters is standard practice... you could also consider pine lning boards if its that bad... lining boards are more forgiving of minor imperfections in out of square/plane surfaces.

and the expense would be huge given it is a large open plan area.

houses cost money to maintain, and money to rectify design/construction problems. sorry but its a fact .
expenses that help reduce maintenance costs and decrease heating/cooling costs have got to be an expense worth doing ?

Posted Friday 17 Jan 2014 @ 4:36:47 am from IP #
Etherealise
Member

Thanks for the comments.

Lots of experience here in how houses cost money to maintain and rectify design/construction problems - we've already spent about $120 k in the first 1.5 years and there is a danger of overcapitalising so we need to think carefully about where the limited funds we have are spent. E.g external blinds are a priority first, for shading. Bear in mind I am not very handy so builders would be doing it.

A flush plaster ceiling covering the rafters would just not look very good here, and while I know that is a favourite bugbear of many to rate aesthetics high, it has to be a consideration if it costs $15k to put in a false ceiling and you don't add value because it looks crap, and then you move house because it added little benefit anyway. If we did do it it would have to be pine lining, which is what's there now. I think that stands a better chance of looking ok but would be better with part of the rafters revealed.

In sum, certainly willing to spend money, but the problem with this place is there's so many factors contributing to heat gain, it's hard to know exactly what are the worst problems to throw money at. Some are obvious like unopenable unshaded windows. I was just a little confused about some of the points about ventilation mentioned above in the original thread and wondering whether ventilation could improve the situation without spending heaps. I suspect ventilation is part of the solution whether a ceiling is retrofitted or not.

The other thing is there is no noticeable problem with heat loss, as the passive solar features work so well in winter - the heat gain that is causing us problems now. If we were freezing in winter I'd be much more tempted to retrofit a ceiling asap. However there are other rooms that could benefit from retrofitting ceiling/insulation and maybe the inside of the cupboard that forms the top of the cathedral ceiling, which as mentioned above is possibly the worst section of the roof because it's the highest point and heat is trapped in the cupboard of the bedroom.

Posted Friday 17 Jan 2014 @ 10:08:10 am from IP #
dave lawrence
Member

always a tough call.. aesthetics vs functionality vs overcapitalising vs might move on anyway .
that's pretty much the story of owning a house for most of us.
one final comment : aesthetics are not only subjective ,but most peoples idea of what looks good changes through time . functionality on the other hand is largely objective and measurable. I know that does not help much !!

Posted Friday 17 Jan 2014 @ 7:56:26 pm from IP #
Etherealise
Member

"aesthetics are not only subjective ,but most peoples idea of what looks good changes through time . functionality on the other hand is largely objective and measurable".

Very true.

Posted Saturday 18 Jan 2014 @ 6:26:44 am from IP #
Eamon
Member

You say you have split roof, is there a roof void in the other section (flat ceilings?) which might be accumulating the heat and in turn radiating it back. Either way, you're best solution would be a good solar powered fan to continually ventilate the areas and minimizing heat 'storage' in the structure's materials. Painting the roof with a special ceramic white will insulate and also greatly reduce thermal UV impact.

Posted Tuesday 21 Jan 2014 @ 1:04:48 pm from IP #
Etherealise
Member

Posted Thursday 23 Jan 2014 @ 6:21:48 am from IP #
milkwood
Member

I'm another one with a problem exposed rafter cathedral ceiling! I have two large living spaces (100sqm and 50sqm)joined by a number of doors and a window. Floor to ridge is about 3m and roof pitch is 17/30 degrees (sawtooth).

The above posts mentioned aesthetics v function and I agree with the sentiments but lets just say that moving away from the exposed beams is non-optional so I am not expecting a perfect solution but I must get some airflow happening.

The Condor Kinetic was mentioned and on their website they seem to offer relief for cathedral ceiling scenarios. I would love to hear experiences from anyone who has installed these units. Any comments much appreciated.

Posted Wednesday 29 Jan 2014 @ 12:38:14 am from IP #
Eamon
Member

Had a look at the condor kinetic, there is an awful lot of generic reading with little about the product itself. It mentions motorised but does not mention any fan system or specs. I cannot see these even meeting whirly bird specs as it is not just wind but 'draw' that would make it effective. Personally the most effective I have sen is solar motorised fans - guaranteed air movement once sun shines, passive air movement all other times. You can pm me for what I believe is the most efficient. With the motorised you could use a simple diffuser, however with all/any diffuser, it needs to be open/closable and also be shallow enough to fit the thickness of roof and structure depth. 3m ceiling is perfectly reachable for diffuser use, it is when you get 4m - 5m, the diffuser becomes a problem to open/close.
Rather than heat removal, have you looked at destratification, i.e. consistent air movement to create even temps and freshness!!!!

Posted Wednesday 29 Jan 2014 @ 1:38:40 am from IP #
nhand42
Member

milkwood said:
The above posts mentioned aesthetics v function and I agree with the sentiments but lets just say that moving away from the exposed beams is non-optional so I am not expecting a perfect solution but I must get some airflow happening.

It's a personal preference but I love the look of skylight windows on cathedral ceilings. Double glazed and motorised, should allow for passive venting during summer.

http://en.wikipedia.org/wiki/Velux

I had something similar in my previous house. The venting isn't mechanical so air-flow is driven mostly by breezes from open windows downstairs. Also they have an R-value of about 1 rather than 3+ as with a standard roof, so slightly worse in winter.

But they looked superb!

Posted Wednesday 29 Jan 2014 @ 3:35:57 am from IP #
milkwood
Member

Eamon, I am considering your product as well.

And nhand42, also considering skylights.

Also considering building a turret at the central part of the roof, a significantly more expensive option.

But it was the Condor Kinetic I was hoping to hear about from purchases as I had not heard of it before reading this thread.

Posted Wednesday 29 Jan 2014 @ 6:29:22 am from IP #
Eamon
Member

No worries, Milkwood. I too would be very interested in hearing about this product and the advantages that were bestowed upon. Information is key and if the product is good, I would like to know too.... A turret, no thats an interesting concept, could you build ducting into it and draw the enclosed heat to lower ground during winter? Thats if the winter requires it.

Posted Wednesday 29 Jan 2014 @ 8:51:25 am from IP #
gazmo88
Member

Saw Saumarez House in Armidale recently:

http://www.nationaltrust.org.au/nsw/SaumarezHomestead

It has venturi vents in the roof. The curator says that when they work they work extremely well and the house rarely gets overly hot in summer.

heat is drawn up through fretted ceiling roses in the centre of each upper room from where it exits.

The flaws in the system are the bearings on which each unit sits which are well past their sell by date, and the absence of a closure mechanism for winter.

Both these areas could easily be addressed.

But it would be a "science project" rather than a "buy off the shelf".

Have lived with Velux roof lights in Europe. Ours had (airtightish) cord operated roller blinds set in tracks just inside the units. Closing the blinds improved thermal performance ... but let in no light. Not important at night of course.

If you fancy a science experiment you might also look into conservatory roof openers. They are wax filled cylinders with a piston. As the air heats up the wax expands, and the piston extends ... opening the vent. Saw a very nice setup at Bayview in Sydney that used these. There was a stairwell in the centre of the house onto which all rooms opened. There were some louver windows at the top of the stairwell operated by the openers. Replacement cool air was drawn into the bottom of the house from below. Owner said it worked extremely well and completely automatically. There was also a manual override. The opening temperature is easily set.

Good luck

Posted Wednesday 29 Jan 2014 @ 9:53:08 pm from IP #
gazmo88
Member

On the subject of ventilators I chanced across this paper comparing various ventilator types which may be of interest :

http://services.eng.uts.edu.au/~phuoc/docs/writings/afmc00120.pdf

note that the "universal venturi" they tested is a different pattern to the ancient one in Saumarez House in Armidale. The latter venturi has a large conical cowl and thus presents a larger surface area to the wind .... at the "cost" of requiring the cowl to turn to face the wind.

Posted Thursday 30 Jan 2014 @ 9:42:09 pm from IP #
bikebec
Member

Hi,
My mum also has a very poorly designed cathedral ceiling with exposed beams- house is boiling in summer and freezing in winter!

The ceiling is lined above the exposed beams with pine lining, and I doubt there is much insulation between the pine and the roof as the house was built cheaply many decades ago, and there looks to be almost no gap between roof and ceiling lining. I would like to install some plasterboard and add insulation (which would make it a flush ceiling).

My question is, do I need to remove the pine lining (which means removing the corrugated iron roof to get at it) for the insulation to work properly? And are there any other important factors (like fire safety) I need to consider if I keep the pine lining?

Many thanks everyone at this forum!
Bec.

Posted Sunday 2 Feb 2014 @ 6:20:15 am from IP #
Bushwalker
Member

I reckon leave the pine lining and put the insulation underneath it.

However, to get the right advice, you need a BAL (Bushfire Attack Level) rating for the house. Above a certain BAL you need a reflective foil barrier and if even higher you need a sealed roof.

If your mum's cathedral ceiling is in the suburbs, it probably doesn't matter, just insulate and plaster board it up. A layer of sisalation would help and don't put the minimum insulation in there, max it out. Cathedral ceilings are notorious for passing heat (and cold).

BW

Posted Sunday 2 Feb 2014 @ 10:32:18 am from IP #

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