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cathedral ceilings & insulation.

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Started 3 years ago by steveisaacs
Latest reply from Ben1

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steveisaacs
Member

Hi all, I have a house with low pitch cathedral ceilings. One of those mildly groovy places that went up in the late 80's with a token nod to efficiency.
It has a multitude of issues that I plan to work through over time, but first and foremost to me is sorting out insulation. There are cathedral ceilings throughout, with deep rafters and thick (25mm) boards laid over. A 35mm batten sits directly on this and between battens is a layer of foil backed fibreglass. The roofing iron fastens straight onto the battens.I'm guessing an R value around 1
Needless to say, the insulation is pretty poor, both thermally and accoustically.

I realise that putting a ceiling in under the deep beams would sort out much of my issues, but sadly I like the aesthetic of those beams.

So version two of my thoughts is to raise the battens by 45 - 90 mm with stand offs to reduce heat and noise transmission plus add more insulation. Tending towards wavecore max silver batts with retroshield aircell as sarking to take the R up to 3 at least. Anyone had similar issues recently or experience with trying to make this kind of roof work properly.

very interested in your collective thoughts

Posted Monday 11 Aug 2008 @ 2:39:21 am from IP #
ghostgum
Member

Not sure about the roof loading issue, but I'd start by using taller battens, just to give you space for the insulation. Spacers would reduce the thermal conduction between the ceiling rafters touching your ceiling and the battens touching the roof sheeting.

Given the cost of actually taking off the roofing, changing the battens and replacing it, I'd try to take it to R4 minimum. What thickness does that require? I think my R4 insulation fluffs up to about 200mm, and then you need an air gap to the RFL.

Posted Monday 25 Aug 2008 @ 6:32:04 am from IP #
Eskimoau
Member

Have you thought about using foilboard? http://www.foilboard.com.au/ConcreteSystems.php

Posted Friday 12 Sep 2008 @ 9:16:03 pm from IP #
gully
Member

I'd suggest foilboards between the the rafters with an air-gap either side. Not sure what you mean by 25mm boards laid over - you mean between the battens and rafters?

Aircell will be hard to retrofit and make it taut, it will sag whereas foilboard will stay straight and maintain that airgap, insulating it better.

Everyone I know with raked ceilings complain about the heat

Posted Wednesday 17 Mar 2010 @ 1:09:13 am from IP #
alfresco24
Member

Aerogel is a compact high performance insulation 'blanket' material that gives high-R for very thin profile.
You may want to target an overall roof/ceiling R value around 5 to 7 given that you have no substantial air gap.
Conducted heat through insulation and roof/ceiling materials is your next biggest enemy, followed by ventilation and air stratification.
Heat circulation in winter, aided by ceiing fans, is also a consideration.

Posted Wednesday 17 Mar 2010 @ 1:27:38 am from IP #
Frateco
Member

Have you considered installing solar roof vents that automatically turn on? If the sensor is positioned at the under edge of the rafter and is set for say 27 deg, then I would imagine you could effectively negate the heat radiation in summer. Obviously for winter you change settings.

http://www.solatube.com.au/homeowner/solarstar.php

If you want to keep the aesthetic effects, this could work. Being solar too means you could do it yourself (if handy)

Posted Wednesday 17 Mar 2010 @ 1:55:01 am from IP #
ghostgum
Member

Using a fan isn't going negate heat radiation in summer.

The radiation transfers heat to the ceiling insulation, and is then conducted through to the ceiling. The fan is going to affect conduction from the air in the ceiling space into the insulation, which is a much smaller component on a hot sunny day.

Posted Wednesday 17 Mar 2010 @ 2:36:33 am from IP #
Frateco
Member

No Ghostgum, with cathedral ceilings, the fan will suck the inside hot air directly outdoors (not into the batts) so the heated air from the heat radiation will be drawn away from the occupant space. You may need 2 fans to do the job but why wouldn't it work?

This same principle can be use in roof space in the same way wind turbines work except it's motorised from solar power therefore you have air movement when the temp increases. Definitely easier and cheaper than ripping roof sheeting off, installing higher battens and putting foil in.

At the end of the day, preventing the heat from coming in always a better solution but I believe this will be easier and cheaper while getting heated air out of the house.

Posted Wednesday 17 Mar 2010 @ 9:08:38 am from IP #
dymonite69
Member

Another way of looking at it.

Solar radiation 1000W/m2.

Now imagine one bar radiator attached to each m2 of your ceiling.

How quickly do you have to move air through the room to stop it heating up? Two fans? I don't think so.

Posted Wednesday 17 Mar 2010 @ 10:25:48 am from IP #
ghostgum
Member

Frateco, the difference between a cathedral ceiling and a flat ceiling is the volume of air above the ceiling. The rest is pretty much the same. I understand that the heated air in the ceiling space is not the main problem. It doesn't conduct heat well to the batts. It is the radiation from the roof onto the batts, which mostly passes straight through the air in the ceiling space.

Posted Thursday 18 Mar 2010 @ 1:05:18 am from IP #
Russell Moore
Member

Paint the roof white?

Posted Thursday 18 Mar 2010 @ 1:18:44 am from IP #
Frateco
Member

"It is the radiation from the roof onto the batts, which mostly passes straight through the air in the ceiling space. "

OK ... and I say that once the heat has passed through into the living space directly under the ceiling, the fans can suck the a lot of the heated air out. If windows are open, you probably get a better result of air movement.

"How quickly do you have to move air through the room to stop it heating up? Two fans? I don't think so." Depending on the fan's capabilities.

I was able to achieve an air change on a commercial job of 10 changes / min over a volume of 4050 cu.m using big-ass fan system. Meaning if you need more than 2, you use more than 2 but it can be done. Since it's solar, the energy impact is still minimal.

Look, I'm trying to give a solution that is not the standard packing the roof with more insulation which is not easy nor cheap. This is cooling by extraction and air movement.

What if he used white insulpaint? http://www.insulpaint.com.au/faq.html

All solutions are valid in one way or the other folks.

Posted Thursday 18 Mar 2010 @ 6:37:12 am from IP #
dymonite69
Member

To achieve cooling by convection transfer, the recommendation is an air flow of 30-60 air changes per hour.

So a 25m2 room with 2.7m ceilings contains 67.5 m3. This would need a fan rated at 33.75 m3/min or 2025 m3/hour. NB kitchen range hoods move between 600-1300 m3/hour.

Posted Thursday 18 Mar 2010 @ 10:31:19 am from IP #
Buzzman
Member

The other issue to think about when increasing size of battens (effectively turning them into purlins) is tha the fascia dn gutter have to be altered to suit, or rainwater will shoot off the roof and into the air, over the top of the existing gutter.

Posted Sunday 28 Mar 2010 @ 8:05:12 am from IP #
Blueprints
Member

Hi Steve,

A lot of merit in many of the ideas above. I'd like to comment but like Gully I'm not sure what you mean by there "There are cathedral ceilings throughout,........and thick (25mm) boards laid over" Are these boards the ceiling material between the rafters? Please could you elaborate on the construction (if any) below the battens(i.e. in between your exposed rafters), so that I can give you my thoughts.

Posted Tuesday 30 Mar 2010 @ 5:30:21 am from IP #
petacat
Member

Just for reference since this started a year ago.

If your cathedral ceilings are like mine then you will still have plenty of space to install many kinds of insulation. Have a look under your roofing and see how much space there is. I have 200 mm between the tiles and ceiling materials which is plenty enough.

It is also room enough to support ventilation but it is more complicated than a normal roof cavity. The support structure divides the roof into narrow lanes going from gutter to roof cap.

A good look under the roofing material will show you what you need to do.

Posted Tuesday 20 Apr 2010 @ 11:30:56 am from IP #
garrechtf
Member

I recently did a home sustainability assessment for a home owner in the outer east of Melbourne with a similar problem. Her home had an old metal roof using Lysaght 406 or similar deep pan deck roofing pitched at about 5º. There was no space between the roof and the ceiling lining as far as I know. To lift the roof and lay blanket she was quoted around $20,000 and because the insulation properties of blanket require an air space between the blanket and the roof to obtain the full R rating of about R1.5 I doubt it would produce the result. She would like to rebuild the roof with a steeper pitch and conventional ceiling space but that would be even more expensive.
In trying to find an affordable interim solution for her I found there were a couple of companies advertising reflective roof paint offering a reduction of radiated heat by providing high reflection factors. I don't know how effective this would be but it is worth investigating.
Two links I can offer which may be worth checking are: http://www.solutionindustries.com.au/Paints/Roof-Coatings/THERMOBOND-Heat-Reflective-Paint-621.htm and http://www.solacoat.com.au At least one of these mentions that the roof will be safe for rainwater collection after the paint has properly dried.

I hope this is helpful to someone.

Posted Tuesday 20 Apr 2010 @ 12:15:12 pm from IP #
munter
Member

Reflective roof paints really need someone like Choice Magazine to get in and investigate. I get the feeling that some products may work but that others are pure snake oil. Prices charged for these products also vary widely. It would be good to get some real, independent test results to get a basis on which to select.

Posted Tuesday 20 Apr 2010 @ 10:08:45 pm from IP #
PeterReefman
Member

If we want to be serious about doing this kind of retrofit properly I think we need to get over the "I like the aesthetic of those beams." line. If it's done well a clean white ceiling (or more timber lining boards) can look fine.

The aesthetics of those beams is stopping the absolutely best solution both in terms of cost effectiveness and thermal performance. Sure we can paint the roof, etc to reflect some summer heat (do it as well), but that's not going to be much help keeping heat in during winter.

We're going to come up against this more and more in the future - people who want solar hot water but don't like seeing panels; people who won't carpet cold polished timber floors because they like the look of that cold polished timber floor; people who like the idea of reducing their energy use but still want to buy a second huge plasma for the kids; etc.

Sorry Steve if this looks like a dig at you (I guess it is a bit), but retrofitting is hard and expensive enough without getting hung up on aesthetics too much. Try to think about the fact that the new super-insulated roof might make you feel BETTER than seeing the beams - and with the savings made by going that way rather than pulling up the entire roofing and extending the battens/fascia/plumbing vents/etc (for a still pretty limited improvement), you will be able to retrofit something else as well and get an over even better result.

All the best

Posted Tuesday 20 Apr 2010 @ 10:27:37 pm from IP #
ghostgum
Member

PeterReefman, the difference in R value between polished timber floors and timber floor + carpet is small. What is different is the perceived warmth when you walk on it with bare feet. Adding under floor insulation does improve that a bit (noticeable when only half our floor was done), but the polished timber floor boards are always going to feel colder underfoot.

Insulating my floor isn't going to make much difference, with the dominant heat loss being through the double glazed windows. Our cathedral ceiling doesn't have exposed beams - posistrut just doesn't have the right look. So we have R4 insulation over the plaster, with a similar sized air gap up to the RFL and battens.

Posted Wednesday 21 Apr 2010 @ 3:36:15 am from IP #
PeterReefman
Member

Hi Ghostgum. Yes that's right. Technically there may not be much R-value difference, and you may only feel it with bare feet, but that's the point.

Actual thermal performance in these things we live in is (or should be) secondary to the real world comfort levels we feel. We live in houses as humans who feel cold when our feet touch surfaces like polished timber, so if we have an already old cold house, it doesn't make sense to have habitable rooms 'feel' colder than they really are.

The problem is that a large amount of us still let fashion dictate what we do (or don't do) in terms of improving our existing housing.

A lot of times we can be blinded to just achieve a mechanical result of a certain temperature range, without taking into account that we can feel comfortable at a wider range if we choose appropriate materials and behaviours. The same is true for heat, with the best example of course being 30c with a breeze is FAR more comfortable than 30c of still air.

With your windows, what kind of drapes/pelmets do you have? I love thermally backed Roman blinds, as they fit nice and close to the arcs and have a perfectly efficient pelmet built into them.

Getting back to the ceilings, yep you wouldn't want to have exposed posi-struts! I've got them as well and like them for their ease of installation and quick service pipe/cable installation as well (to cut down on expensive plumber and electrician labour!). Did you use the 250mm high ones?

Posted Wednesday 21 Apr 2010 @ 5:19:51 am from IP #
ghostgum
Member

3 rooms have Roman blinds, but I don't think my wife used thermal backing.
The main rooms have full length drapes with bonded thermal backing (i.e. not lined), below pelmets. Our bedroom has drapes without pelmets. Instead of Roman blinds (the cheap option when your wife makes them), I'd probably choose cellular blinds now.

The posi-strut beams are about 300mm deep. I'd need to climb up into the adjacent ceiling space to measure them. Yes, the electrician just poked his wires through the gaps, and insulation was stuffed between the cables and the ceiling battens.

Posted Wednesday 21 Apr 2010 @ 5:51:04 am from IP #
wangtrader
Member

The simplest and most cost effective solution to insulation is a product I recently applied directly to the roof, walls and underfloor of my aunt's house in Maldon Victoria. With an R-rating equivalent to 6-8 inches of fibreglass, it's no suprise that the temperature of over 50C on a hot day, was reduce to 23C. The airconditioner is now never needed. No changes needed to the roof and it lasts for 20-30 years.
I have photo's and further info if anyone is interested.
Wangtrader

Posted Tuesday 4 May 2010 @ 1:17:20 pm from IP #
Frateco
Member

what was the product?

Posted Sunday 16 May 2010 @ 11:48:19 pm from IP #
acd
Member

I have an 80s house, just outside Melbourne which has the exposed beam cathedral ceiling. I want to put up plasterboard on the inside and use that space for insulation. Once the plasterboard is up then obviously I cant access the space, so want the insulation to be good. The main problem is really heat in the summer, more so than cold in the winter. Batts I think are better for the winter problem, and Im not convinced they will adequately prevent the summer heat. What should I put in? There is quite a good depth available.

Posted Monday 31 May 2010 @ 11:44:33 am from IP #
GBD
Member

Acd, I think the best option for your place would be to use poly or glass bats with foil on top (the integrated stuff would be easiest) and then you can have an air gap above it between that and your existing ceiling as I assume you've got something like 250 to 300mm deep beams. And you might be surprised that you've already got sisalation under your tiles / tin roof and I'd think it's a lack of air space and insulation in general that's causing your summer heat issues.

Posted Tuesday 1 Jun 2010 @ 12:14:20 pm from IP #
acd
Member

Hi GBD, thanks for that. Yes you are right, the beams are quite deep.Can I get batts with foil already attached to one side? is that what you mean? Otherwise do can you suggest a particular make of foil product to use with my batts? I have previously used the stuff which is like giant bubble wrap but with silver on both sides (its not cheap though)

Posted Wednesday 2 Jun 2010 @ 10:15:43 am from IP #
GBD
Member

Yes you can get batts with foil already attached. Foil side up in your instance.

This doc should help you a bit -

http://www.sustainability.vic.gov.au/resources/documents/Insulation_types.pdf

Standard silver sisilation foil bonded to the batts or roll of insulation would do IMO - and would be easiest to install without lots of mucking around. I prefer poly as it is normally made from recycled pet bottles or such like.
Install a sheet of gyprock, slide in some insulation make sure it fits snugly, then up goes the next sheet etc.

Posted Wednesday 2 Jun 2010 @ 1:34:02 pm from IP #
acd
Member

Thanks, Ive been looking on the web and making a few phone calls and cant find anyone who makes or sells poly with foil backing. Using poly batts and aircell would be quite expensive and more fiddly to install. What about this aerogel product - I know its expensive but looking about the same cost as the poly R4/aircell option (presuming I will be charged more for that installation also). Is aerogel as good as it sounds?

Posted Friday 4 Jun 2010 @ 6:53:30 am from IP #
Frateco
Member

Yeah you can't get batts with foil, only blanket rolls. And by the way, they don't just slide in - they catch on anything , bunch up and are a pain in the ass.

Although there is an extra cost, get the foil-lined blanket rolls, trim to suit rafter centres and timber batten the ceiling space. This gives you the freedom to pull the roll through as well as keeps electrical at a lower plane to the foil.

Just an idea.

Posted Friday 4 Jun 2010 @ 7:11:15 am from IP #

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