Dec 12, 2018: More About Keeping Cool

In last week’s Newsletter we critiqued an article from Domain.com.au about ‘Tips and Tricks to Keep Your House Cool the Natural Way’ and we offered a few suggestions of our own. In response I received the following comments from a long-time reader and valued supporter named Marcus who wrote:

Dear Andy,

A good summary of much that can help in the heat, but a painful reminder of the fact that many of our houses are just not built ‘the right way’.
I have a few points.

1. Blinds – Not everyone would like the double cell ones, and I find that single ones with light coloured curtains closed behind are quite effective. Like you we choose not to live in the dark.
2. uPVC window frames. I think the evidence from other (sunny) countries is pretty convincing. uPVC is very stable in the long term and beats thermal break aluminium – looks good as you can get it in white and wood effect and is easy to clean, unlike aluminium which tends to look dull and ‘pitted’ with time. My only issue is that the frames tend to be thicker, which means less glass area.
3. Fans. We use fans to remove hot air from the apex of our living room and first floor landing (Both can get very hot as the roofs are not well insulated). This hot air is delivered to the ‘whirly gig’ attic fans and thence to atmosphere. This would probably be even more effective if we had powered (solar or mains) fans in the roof.
4. Roof insulation. Obviously you can add more insulation material to attic floors. Our problem is the ‘cathedral’ ceiling, which suffers from being under quite dark tiles and not much insulation. I don’t have an IR camera, but I expect it would be a horrifying as your photo. You could add thick insulation between the trusses, but this would destroy the look of the room. Do you know of any materials which offer significant insulation, but would leave the trusses exposed?

Keep up the good work.

Marcus makes some good points and is absolutely right that many Australian homes are not built the ‘right way’ for our hot and sunny climate. As I mentioned in last week’s article, a brick veneer house with a dark tile roof is about the most inappropriate way to build for Australian conditions and yet that is exactly how the majority of new homes are still being built. Heavy masonry materials like brick and tile soak up heat throughout the day, store that heat around the outside of the home and then radiate the heat into the house until long into the night. This causes the house to stay hot and the a/c to work overtime. Combine this with your typically awful Australian insulation job (and the fact that no thought is given to air sealing) and you get a house that either gets unbearably hot (and stays hot for most of the night) or uses a heap of electricity to run the air-conditioning far more than is necessary.

I would just like to add a couple of things to go along with Marcus’s comments.

On the subject of uPVC windows, I know some people (like Marcus) who are very happy with their uPVC windows. But I also know an equal number of people who are not so happy. I think the key with uPVC is to keep the size of each pane of glass relatively small. I’ve seen brand new, imported, European uPVC frames that have sagged in the middle when they have particularly wide, horizontal sashes. I’ve also seen uPVC soften slightly in extreme heat causing frames to sag, usually when the sashes are large and heavy. Marcus is right that uPVC will transfer much less heat in and out of the building than aluminium so their energy performance is better, I just suggest that if you use them you keep your window sash sizes smaller to hopefully avoid the sagging issues.

This is clearly an extreme case of uPVC window sagging but it shows what can happen.

Regarding the use of exhaust fans to cool your house… yes Marcus is right that they can be very effective at expelling hot air but it is very important to know what the temperature both inside and outside the house is when you turn them on. Whenever you blow air out of a house, you suck an equal amount of air in from outside. So if the outside air is hotter than inside, you will simply be sucking in hotter air than what you are blowing out. This is why I think it is essential for every house to have an indoor and outdoor thermometer so you know when to turn on fans and open windows (i.e. when the outside air is cooler than inside) and when to leave them off or closed (i.e. when the outside air is hotter than inside). In fact I wrote a Newsletter article about this exact subject back in February last year titled ‘Every Home Needs This‘.

And finally, to answer Marcus’s question about improving roof insulation in a cathedral (sloped or raked) ceiling…

Cathedral ceilings are extremely difficult to build well and to insulate properly and even more difficult to retrofit to a high performance standard. As Marcus points out, he could add a lot of insulation to the underside of the existing ceiling but it would ruin the look of the exposed ‘trusses’. So the answer would be to try to add the most insulation between the rafters with the least amount of depth. The two insulation products that have the highest R-value per inch (25mm) are two kinds of rigid foam. One is called Extruded Polystyrene and the other is called Polyisocyanurate. With both of these products you get about R2.4 insulation in only 50mm of foam (as opposed to about 100mm of fibreglass batt). So Marcus, if there’s room to add 50mm of depth to your ceiling this would be the way to go however then you’ve got the problem of having to cover the underside of the insulation with gyprock or T&G or some other product and this can turn a ceiling insulation job into a major construction project.

This is one of the reasons why I generally prefer a trussed roof with a flat ceiling and an attic space rather than a cathedral ceiling. When you have an roof space you have the ability to get up there in the future and make changes to things like the insulation or the electrical wiring which you can’t do with a cathedral ceiling.

Thanks Marcus for adding those thoughts. We always welcome any feedback and comments.