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Double Glazing in Canberra’s new homes?

By Solacecreations 11 August 2011 35

We all know the benefits of double glazing.

Why are builders still allowed to put single glazed aluminium into new homes in Canberra?

100% of your heat escapes through a single glazed unit.

Maybe they shouldn’t put in wall or ceiling insulation either as the outcome is the same.


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Double Glazing in Canberra’s new homes?
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jason.edu 12:11 am 31 Mar 17

I know I am digging up a really old thread but came across this comment while searching the web. It did make me stop and do further research to understand windows. However after doing this I believe this post is wrong even if it is shrouded in (incomplete) physics.

“double glazing stops heat transfer but not light transfer”

All glass stops light transfer, more specifically it blocks the wavelength of light/heat that is transmitted by the sun. The amount that is blocked is measured using the SHGC. From the WERS website the best single glazed unit has a SHGC of 0.85 – or 85% of this type (or wavelength) radiation gets through. The best double glazed unit has a SHGC of 0.69. Going with a double glazed unit will reduce the solar gain received from a north facing window.

This needs to be offset against radiant heat and its transfer through glass. This is measured by the U value. This is of course where double glazing offers a clear advantage. The lower the U value the better. Gunghalan Al this is what you are referring to in your post.

In theory a window with a SHGC of 1 and a U value of 0 would allow 100% of the solar radiation into the house but not let any radiant heat transfer in or out. Obviously this type of window doesn’t exist.

What Strine is arguing is that the loss in solar heating (SHGC fall) is not made up by the savings in radiant heat loss (U value decrease). I think part of this design also includes insulated window coverings for when the sun isn’t shining – so assumes these are shut at night reducing the heat loss and effective U value of the window & coverings. Keep in mind good window coverings are just as good as double glazing but a lot cheaper.

I don’t think it is right to say one is better in all situations. Its going to depend on the two glazing units you are comparing, the amount of sunshine, as well as the temperature differentials at different times of the year. Rick (from Strine) has run the calculations for Canberra with assumptions on the amount of sunshine etc and thinks it works. These are on his website. Clearly if you had a month of cloud his assumptions would be wrong and a double glazed unit maybe better (I havn’t run the numbers to confirm), but on average we don’t have that issue in Canberra, so on average a single glazed unit would be better using his assumptions and calcs.

The standard approach is to use the same glass throughout the house. But actually we need specific glass for specific orientations. Its never right to say one window is better for every possible situation/orientation/climate. It depends. It is a complicated area and it has been highlighted to me when trying to talk to builders and designers – because generally they don’t know and cant offer advice (which is why I am here).

Gunghalan Al, I do think its a bit rough the way you had a go a Strine without complete information – you have a useful view but I think you played the person too hard particularly when the information you used was incomplete.

And no I am not associated with him 🙂

Gungahlin Al said :

bugmenot said :

Builders also do strange things, like double-glaze only the south facing walls instead of all around.

Unfortunately that comes from certain misinformed architects, the likes of Ric Butt in particular who claim that “you don’t want double glazing on the north windows because it would stop the heat of the sun getting in” (direct quote, to me, by one of his architects). No understanding of the physics of light.

Unfortunately local architect Ric Butt (Strine) also gave the same line to Sanctuary magazine and they printed it http://www.scribd.com/doc/21370093/Sanctuary-magazine-issue-9-The-Millennium-House-Canberra-green-home-profile

I took them to task over it and they conceded that it didn’t sound right at the time but they went with it. As a result, they ran a full feature article about window types next issue, in which they corrected the error http://www.scribd.com/doc/25739197/Sanctuary-magazine-issue-10-Windows-that-work-green-home-feature-article

Just to make it clear: double glazing stops heat transfer but not light transfer. The sunlight pours through double glazing almost unencumbered, hits everything inside and is remitted into the inside airspace as long-wave infrared light = heat. This is radiant heat. This is why double glazing is no help in summer if it is in direct sunlight. The light comes in, everything gets hot, and the heat can’t get out again. You must shade all windows possible from direct summer sun. The EER rating picks this sort of thing up and penalises the rating heavily.

Back to the physics of light/heat. Heat moves from the hotter side (more energy) to the colder side (less energy – where the air molecules can move around with more elbow room and less bouncing into each other if you like). This is mostly by conductivity. If you have single skin glass the heat loss in winter is phenomenal. This is another reason why Ric Butt’s advice is so critically wrong. If it is 40 outside in summer and 20 inside, single skin glass will do a superb job of conducting that heat straight into your home – irrespective of how well shaded the window is. An improved window – as long as it is shaded – will reduce this transfer.

So what happens in some of Ric Butt’s designs is the people have their blinds all draw all day through summer living in darkness to try to compensate for the error. And they don’t get anywhere near the benefit they should from the winter solar access.

Laminated low-e is better than single skin. Double glazing is better again. DG with low-e better still. That plus with argon gas filling better still. And framing with a thermal break will also reduce some 25% heat loss that ordinary aluminium framing has. That’s either wooden frame, two-piece aluminium with a plastic bit sandwiched between, or PVC. It comes down to how much you can afford. Put money into better windows before many other essentials that can come afterwards.

Spiral 10:00 am 20 Nov 12

Solacecreations said :

There is a comprehensive ACTPLA publication called: Building Better Homes in Canberra. This is what they say:

Winter heat loss through various glass treatments . . .

Do you realise that the figures you are quoting, as impressive as they are, do not support what you originally posted?

I’m sure you know what you meant, probably everyone here knew what you meant but what you wrote probably wasn’t what you meant to say.

Sure we could correct you but as you have obviously followed this thread and still haven’t spotted the error in what you posted, I get the feeling that attempting to explain what was wrong in the OP would be a frustrating experience.

Besides many people find it amusing to watch “experts” make asses of themselves.

Go back and really read what you originally posted. Sit and think about it, then correct and resubmit.

King_of_the_Muppets 9:14 am 20 Nov 12

The EER rating is just a tool which gives a rating for the home as a whole system.

It is far from perfect but its a start. It limits very poor performing buildings but doesn’t neccessarly provide a very accurate reflection of how good a home is.

Another key item to consider is that when high spec glass is used the frame transfers more energy than the glass. If your going down this path make sure you use thermally broken aluminium at a minimum but timber and PVC are far better. There are plenty of sources which you can use to review this – I think the best is the WERS website – http://www.wers.net/ – The U and SHGC values are the values of importance – the lower the better.

Solacecreations 12:42 pm 04 Nov 12

I love how you think Gunghalin Al and you clearly know what you are thinking. There are a heap of ways to get your EER to 6 without double glazing and builders and architects know the tricks. What I can’t explain to my clients is the feeling of “comfort” that a well insulated home provides. They have an even temperature, no condensation and no draughts. I have just moved from my lovely insulated home that was double glazed and had hydronic heating. I am now in a rental for 12 months that has no eaves, standard insulation, single glazed aluminium windows and ducted gas heating and cooling. I am having a massive shock to my system. The upshot is that I can see how the less fortunate people live who have purchased a standard project home.

michellecanberra 1:49 pm 26 Nov 11

2604 said :

Gungahlin Al said :

At that time the “thermally improved” (read: don’t leak through gaps as much) G James frames and laminated low-e windows cost us $11K more than the standard Stegbar leak-like-a-sieve crap the building offered up.

I’m not convinced that the ROI on double glazing justifies the expense. We could pay our entire annual gas heating bill (for our 70s spec-built house with single-glazed windows and DGH) on the interest earnings from $11,000 invested in an online savings account earning 6.51%.

What you are missing is the comfort that you experience from having an insulated home. Windows need to be insulated also. Next time don’t insulate your walls either and you can save even more. I am a double glazing convert and I wouldn’t go back to single glazing

Solacecreations 12:28 pm 07 Oct 11

Spectra said :

100% of your heat escapes through a single glazed unit.

The who to the what now? What in blazes are you talking about? 100% of your heat? Are you seriously suggesting that every surface in your house other than single-glazed windows is a perfect insulator? And that no air could possibly escape or enter? Geeze – I can’t help but wonder what the hell I’ve been breathing, since the oxygen should have run out ages ago.

Seriously, I know you’re truing to spruik your double glazing business under the guise of concern for the environment, but please: at least try to make your ridiculous claims sound slightly plausible.

There is a comprehensive ACTPLA publication called: Building Better Homes in Canberra. This is what they say:

Winter heat loss through various glass treatments
Unprotected single glazing 100%
Vertical or ventian blinds 100%
Unlined drapes or Holland blinds, no pelmet 92%
Heavy lined drapes, no pelmet 87%
Unlined drapes or Holland blinds, pelmets 79%
Double glazing 69%
Heavy lined drapes, pelmet 63%
Double glazing with low-e coating 57%
25mm Polystyrene shutters, good airseal 50%
Double glazing, heavy drapes, pelmets 47%
Single glazed industry typical aluminium 100%
Singe glazed thermally improved aluminium 87%
Single glazed timber or P.V.C 82%
Double glazed industry typical aluminium 72%
Double glazed thermally Improved aluminium 60%
Double glazed timber or P.V.C 54%

I hope this helps those critics of mine. I am frustrated because it is easy to get a 6 star rating in a new home through working around the glazing calculator and using different insulation etc, however, extensions seem to be more under scrutiny. I am seeing more people doing extensions that are unable to get the green tick through using single glazed aluminum windows.

You are right about the Certifier needing to make sure the calculator is correct and they approve the glazing used. If you have selected double glazing then you probably met the requirements and it wasn’t discussed.

As for being a supplier in Canberra and being able to voice my opinion – I am also a consumer and a person passionate about energy efficient homes. I am baffled why project builders don’t see the benefit of building a home that will save money and energy for clients just by using smarter products.

Our uPVC price is getting very competitive with single glazed aluminium windows, however, many builders in Canberra don’t like to use anything other than the products that they know and love. I often have clients coming into my showroom saying that their builder doesn’t believe in double glazing, energy efficient cladding, solar hot water etc etc. Having said that, there are a growing number who are green builders and open minded.

Before everyone criticises me about this, I am married to a builder so I am in the industry already.

With regards to double glazing particular parts of the home, the most important outcome is to seal your whole building envelope so that your precious heat in winter can’t escape. This is through insulating the walls, ceiling, windows and floor and sealing for draughts. If you leave some areas single glazed then it is a no brainer where your heat will go. This includes bathrooms and toilets that don’t seem as important to people.

kakosi 1:18 am 19 Aug 11

I replaced my old windows with double-glazed windows and notice no difference in heat/cold proofing. Perhaps the quality of the double glazing in Australia is different from that overseas?

Innovation 11:15 am 13 Aug 11

milkman said :

2604 said :

Gungahlin Al said :

At that time the “thermally improved” (read: don’t leak through gaps as much) G James frames and laminated low-e windows cost us $11K more than the standard Stegbar leak-like-a-sieve crap the building offered up.

I’m not convinced that the ROI on double glazing justifies the expense. We could pay our entire annual gas heating bill (for our 70s spec-built house with single-glazed windows and DGH) on the interest earnings from $11,000 invested in an online savings account earning 6.51%.

And this is the issue. double glazing is very expensive, and there are others ways to reduce heat loss. Having decent window coverings (e.g. curtains) goes a long way. Ceiling and wall insulation also make a heap of difference. Also, you should plan to heat only the rooms you use, and keep other doors closed. Do this things and you’ll get a good result. Double glazing is good, but it’s only part of the answer.

Double glazing is expensive and I really feel for people who can’t afford it. However, unless the curtains are open on a sunny day, you won’t get any heat from the sun to heat up any thermal mass in the house. (Even a few minutes of sun can make an extraordinary difference to heat retained in any thermal mass and the overall temperature of the house). With inefficient windows such as single glazing, any heat gained during the day is soon lost back through the windows (ie because the curtains are open). Of course if you close the curtains because it is cold and windy outside then you don’t gain the radiated heat during any sunny moments during the day.

Even on days when it doesn’t even get above 10 degrees (not taking account of wind chill), 30 minutes of sun during a day can easily get a house to well over 20 degrees and keep it there.

milkman 9:09 am 13 Aug 11

2604 said :

Gungahlin Al said :

At that time the “thermally improved” (read: don’t leak through gaps as much) G James frames and laminated low-e windows cost us $11K more than the standard Stegbar leak-like-a-sieve crap the building offered up.

I’m not convinced that the ROI on double glazing justifies the expense. We could pay our entire annual gas heating bill (for our 70s spec-built house with single-glazed windows and DGH) on the interest earnings from $11,000 invested in an online savings account earning 6.51%.

And this is the issue. double glazing is very expensive, and there are others ways to reduce heat loss. Having decent window coverings (e.g. curtains) goes a long way. Ceiling and wall insulation also make a heap of difference. Also, you should plan to heat only the rooms you use, and keep other doors closed. Do this things and you’ll get a good result. Double glazing is good, but it’s only part of the answer.

Innovation 11:33 pm 12 Aug 11

Gungahlin Al said :

One key downside of single or laminated glass that should be considered is that the thin layer and resulting high tempoerature gradiant across it means you get condensation – a lot of it. A problem that just doesn’t exist with DG. And if your builder uses crappy cheap MDF architraves instead of timber, you just know what that condensation is going to do!

That was one surprise aspect that we hadn’t thought of or expected with our DG. In our previous house our windows were covered in water in winter and the house felt damp from all of the condensation. (I can remember a new ACT resident once saying that they knew they were in trouble when they woke up and found ice on the inside of their windows). Our DG windows don’t get any condensation on them.

I know that a lot of people can’t afford insulating features like DG. I haven’t done the sums but, if possible, I suspect that it might work out cheaper to build a smaller house with as many energy efficient feaures as are affordable and then extend later, rather than build a bigger house initially and then later retrofit features like window frames that can accommodate IGU’s.

The other thing that we have noticed is that the benefits from a solar passive house can’t just be measured by monetary cost. For example, in winter, unless the heating is radiated any artifical heating is not likely to be as pleasant as solar radiation. Heated air which is very temporary is rapidly lost (eg, when the heating is turned off), the movement of air creates a draft which requires additional heating to compensate, heated air is uncomfortably dry and there are hot and cold pockets throughout the house. Artifical radiated heating such as in slab electric is very very expensive to run and hydronic heating is very expensive to install. Coversely, our friends are always surprised when we have to open our windows in winter to cool our house down – which increases the fresh air in our house.

2604 6:37 pm 12 Aug 11

Gungahlin Al said :

At that time the “thermally improved” (read: don’t leak through gaps as much) G James frames and laminated low-e windows cost us $11K more than the standard Stegbar leak-like-a-sieve crap the building offered up.

I’m not convinced that the ROI on double glazing justifies the expense. We could pay our entire annual gas heating bill (for our 70s spec-built house with single-glazed windows and DGH) on the interest earnings from $11,000 invested in an online savings account earning 6.51%.

ThisIsAName 5:49 pm 12 Aug 11

Gungahlin Al said :

Downlights are your killers. Change the halogens for compact flouros (or LEDS if they are affordable yet – haven’t looked for a while), then also get the plastic cowls that fit over the hole. The cowls stop the draft but you can’t put them over halogens because they are too hot – they chew through enormous juice too. Once the cowls are in place you can stuff a bunch more insulation right up the them.

Ooops – the type of light I meant to describe is a “recessed light” (whatever the proper term is). I’m thinking of the type of units which take a typical light bulb, and have a metal housing up in the roof space (sorry – can’t find a good enough image to link to). Half a dozen of these leaves just as many holes in the roof insulation & hello additional heat loss. I can only assume they are relatively cheap, which is probably why the builder used them. A quick google hinted at recessed units designed to enable insulation to be installed around them.

Anyway, the reported performance difference between my “5*” and your 5.5* is fairly big…

Gungahlin Al 3:03 pm 12 Aug 11

ThisIsAName said :

We are renting in one of the newer houses (2 yrs old) with a high EER, but the heat loss is absolutely shocking. The attic has plenty of insulation

Out of interest, what is your EER and heat loss in general terms? (eg. temperature drop overnight)

On paper, my place has a 5* EER, but I think the heat retention should be better (to my untrained eye). The place can be heated to ~19-20, the heating turned off, and it’ll drop to 10-11 by morning. This is only ~2-4 degrees better than a somewhat refurbished 50 year old (?) place I once rented in the inner north. I can’t find the EER, but it would be <= 3. My current place has R4 ? ceilings, R1.5 walls and single glazed aluminium windows (with pelmeted curtains or insulating blinds).

This story appeared recently on the 7:30 report, which may be relevant:
http://www.abc.net.au/7.30/content/2011/s3200765.htm

I've found gaps in the roof insulation:
* 30-40cm squares cut around the drop lights
* cutouts for fans (though the insulation is snug against at least one of the pipes)
* there is an uninsulated gap under a wooden platform that the central heater is mounted on

It'd be useful to know how much heat is lost there & if something similar to the link above is happening.

——

Gungahlin Al: you recently posted here http://the-riotact.com/8-overnight/51151 that your place only dropped to 16 overnight. What is your place rated at?

Only 5.5. But it runs only 11 degrees off east-west, every living space and bedroom is on the north side, which is pretty much a wall of glass. But there is also a large overhang to prevent midday summer sun getting in them.

The south and west sides have much smaller windows, all shaded with very little direct summer sun hitting them – will be zero when the trees get up a bit higher. No windows on the east end – garage.

It should not drop as far as 16 but I have to get some insulation around a heat transfer kit I put in to suck hot upstairs air and dump it down in the laundry/bathroom area. Just been a bit slack.

Downlights are your killers. Change the halogens for compact flouros (or LEDS if they are affordable yet – haven’t looked for a while), then also get the plastic cowls that fit over the hole. The cowls stop the draft but you can’t put them over halogens because they are too hot – they chew through enormous juice too. Once the cowls are in place you can stuff a bunch more insulation right up the them.

Get DraftStoppas to fit over your exhaust fans too – another gaping hole!
Make sure any flues (like where your kitchen exhaust goes outside) have self-closing flaps on the outside too.

ThisIsAName 2:31 pm 12 Aug 11

matjones said :

Ceej1973 said :

KB1971 said :

On of the reasons the whole EER system is a crock…..

+1. We have double all round, and to think that one of those dual occupancies in the newer areas with hardly any nth/nth wst windows can have the same energy rating as us. Pfft.

We are renting in one of the newer houses (2 yrs old) with a high EER, but the heat loss is absolutely shocking. The attic has plenty of insulation

Out of interest, what is your EER and heat loss in general terms? (eg. temperature drop overnight)

On paper, my place has a 5* EER, but I think the heat retention should be better (to my untrained eye). The place can be heated to ~19-20, the heating turned off, and it’ll drop to 10-11 by morning. This is only ~2-4 degrees better than a somewhat refurbished 50 year old (?) place I once rented in the inner north. I can’t find the EER, but it would be <= 3. My current place has R4 ? ceilings, R1.5 walls and single glazed aluminium windows (with pelmeted curtains or insulating blinds).

This story appeared recently on the 7:30 report, which may be relevant:
http://www.abc.net.au/7.30/content/2011/s3200765.htm

I've found gaps in the roof insulation:
* 30-40cm squares cut around the drop lights
* cutouts for fans (though the insulation is snug against at least one of the pipes)
* there is an uninsulated gap under a wooden platform that the central heater is mounted on

It'd be useful to know how much heat is lost there & if something similar to the link above is happening.

——

Gungahlin Al: you recently posted here http://the-riotact.com/8-overnight/51151 that your place only dropped to 16 overnight. What is your place rated at?

djk 10:38 am 12 Aug 11

Also, is it really acceptable for someone who states in their profile that they sell double-glazed windows to be starting this topic? And also spreading (apparently) false information in regards to single-glazed windows letting 100% of the heat escape?

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