Double glazing vs single pane of low-e glass? « Alternative Technology Assn Forums

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Double glazing vs single pane of low-e glass?

(10 posts) (8 voices)

Started 6 years ago by woobar
Latest reply from Morbo

Tags:

double glazing

woobar
Member

Hi - I would love advice from all your clever people to help me determine what type of glazing is best suited based on window orientation / window shading etc.

I need to replace ALL my windows at home with new glass, the existing glass is not safety glass so it's a risk for my children and I also want to increase the thermal performance of my home.

I have been doing a lot of research to get a better understanding on the performance of

(1) single 6mm low-e glass

versus

(2) double glazed unit (6mm / 12mm argon / 6mm low-e ) - I am using 6mm as I am in a high bushfire risk area.

Based on my research the SHGC value for single versus double glazing is the same.

The benefit of double glazing is in heat retention (U-value), my data says heat retention is twice as good with a double glazed unit.

My situation
- 2 story home in victoria. lower level mudbrick / second story weatherboard

- Brick floors throughout on lower level

- A deep verandah spans the length of my house on the north side blocking all sun from entering the down stairs rooms - my house is very comfortable in summer!

- I have no roof cavity or insulation - tin roof / foil sarking / timber ceiling

- A large majority of rooms are unheated/uncooled and majority of windows receive no direct sun as they sit behind the large verandah.

- I actively manage my environment during the year...
-- In summer - I close all curtains that receive direct sunlight, close windows during the day and open and night on north/south side to cool house overnight.
-- In winter - I open curtains that receive direct sunlight during the day and close all curtains at night.

- I am in the process of draft proofing all the doors and little gaps that come with an old rustic built muddie.

==========

Where I am struggling is where should I put double glazing vs use a single pane of low-e. Or should I just go the cheapo option and use 6mm laminated glass?

Is the cost of double glazing worth it considering a large portion of the rooms in the house have no cooling/heating and my roof is a not insulated?

Thanks in advance for your comments!

Posted Thursday 6 Aug 2015 @ 12:17:00 pm from IP #
decerebrated
Member

You know how in winter you get condensation on the inside of you windows when you have the heater on? That just doesn't happen when you have double glazing. The cost difference between single and double glazing isn't what it used to be. All our windows are double glazed and it makes a huge difference to both thermal and acoustic insulation.
A block of units I know needed new windows and the difference in quotes for single and double glazing was only about 10%
I would never have single glazing by choice again

Posted Sunday 9 Aug 2015 @ 2:56:43 am from IP #
Annette
Member

If you want to improve thermal performance, get double glazing but addressing the other insulation probably gives bigger 'bang for buck'. Can you insulate,the ceiling?

You haven't mentioned whether the house is uncomfortable or not in winter? Or whether you are concerned about the cost of heating, or might be concerned in future...If you are planning to stay in the house it is probably good to bite the bullet and get double glazing if you are replacing the glass anyway. At least get some quotes.

I'm not sure that normal height windows ( ie half height not floor to ceiling height ) are really dangerous for children, unless you have extremely adventurous children who are launching themselves off tables at the windows!

Whichever decision you make, if you have full height windows/doors, put visibility decals on the glass at child height so they don't run into it accidentally - running into a laminated panel might be less dangerous but can still hurt!

Posted Sunday 9 Aug 2015 @ 3:21:38 am from IP #
dlvb19
Member

I don't know where your research is coming form but SHGC is definitely not the same for SG vs DG. For god sakes use the WERS data online and do not believe the claims on retailers websites. SG has SHGC of about 0.7 vs DG with about 0.45 from memory. Although as you pointed out the DG will retain heat for longer. If a particular window gets plenty of direct sun the maybe consider SG. If not then DG.

If you can get DG for less than 25% extra then go for it! Probably won't make a huge difference to your performance but you will never have to second guess yourself. Silence those annoying voices in your head. Also potential buyers will appreciate.

As other commenters suggested. Forget the windows and insulate the roof. Also consider external insulative shutters. Will get way better R values for way less money than a full window swap

Posted Sunday 9 Aug 2015 @ 4:17:54 am from IP #
Annette
Member

Hi Woobar

The WERS site (FAQs) http://www.efficientglazing.net/EGhome.aspx says:

'Low Emmisivity Glass is not better than double glazing. Double glazing gives better performance for your windows. Double glazing can also be used in conjunction with Low Emmisivity Glass to achieve better performance results.'

The WERS site is very worthy but quite complicated to navigate.

Posted Sunday 9 Aug 2015 @ 6:45:36 am from IP #
Miglas Windows
Member

dlvb19 said:
I don't know where your research is coming form but SHGC is definitely not the same for SG vs DG. For god sakes use the WERS data online and do not believe the claims on retailers websites. SG has SHGC of about 0.7 vs DG with about 0.45 from memory. Although as you pointed out the DG will retain heat for longer. If a particular window gets plenty of direct sun the maybe consider SG. If not then DG.

If you can get DG for less than 25% extra then go for it! Probably won't make a huge difference to your performance but you will never have to second guess yourself. Silence those annoying voices in your head. Also potential buyers will appreciate.

As other commenters suggested. Forget the windows and insulate the roof. Also consider external insulative shutters. Will get way better R values for way less money than a full window swap

Hi Dvlb19 - This is not 100% correct,

From a SHGC difference in Double Glazing versus Single Glazing, whilst there is a minor improvement - it is almost negligible.

When comparing WERS figures from two different systems they are rated on standard sizes (e.g. Awning = 1500W x 600W). If you can now imagine you have two different systems at this size rated (one Single glazed, one Double Glazed) at this size. The DG Frame might be "bulkier" than the other. This means it has less of a glass proportion to frame for that size, and therefore has a lower SHGC (due to less glass area at the same size).

The other thing to consider with WERS is if you have a Window rated at SHGC 0.7 (based on 1500x600) but then opt for a window that is twice that size e.g. (1500x1500) Your SHGC in reality will be much higher as the glass to frame proportion is now larger.

In reality, if you look at *glass only* the difference between single glass and an IGU:
4mm Clear (Single glazing) - U Value = 5.9 SHGC = 0.85
4mm/12mm Argon/4mm - U Value = 2.6 (~56% reduction) SHGC = 0.75 (~11% Reduction)

As Annette mentioned, LowE glass is not better than Double Glazing and you can always specify LowE glass into an IGU for even better performance.

*glass only* figures
4mm EnergyTech (Single glazing) - U Value = 3.7 SHGC = 0.73
4mm/12mm Argon/4mm EnergyTech - U-Value = 1.6 (~57% reduction) SHGC = 0.64 (~12% reduction)

The other thing which is often overlooked is that a typical Double Glazed window has more efficient gaskets and seals as well as higher quality hardware compared to a basic single glazed window. This means they "leak" less energy. For example a generic Window on the market would have an AI (Air Infiltration) Rating of 5.0. The Miglas AliClad system can achieve a rating of 0.07 - one of the lowest on the Market.

Double Glazing always outperforms single Glazing, so as long as your budget allows it is a worthwhile investment.

Thanks,
Kurt Miglas
Miglas High Performance Windows & Doors

Posted Monday 10 Aug 2015 @ 12:22:15 am from IP #
woobar
Member

Thanks everyone for your comments and advice, it's greatly appreciated.

I have definitely considered insulating the roof but as it's timber lined with exposed beams it would involve adding a false ceiling. This would be very costly, change the appearance of the house and be quite difficult as half of the house has a cathedral ceiling.

All my windows are floor to ceiling, very old and a danger at the moment so I definitely need to swap these out regardless of whether I insulate the ceiling.

The house is definitely uncomfortable in the winter but this is probably because we try to live sustainably/economically and minimise the use of the heater! The only room that is heated is the main kitchen/living space using a wood firebox and sometimes a split system. This is also the only room downstairs that receives any direct sun - through the top ceiling windows.

The remainder of the downstairs rooms receive no direct sun due to the wide north facing veranda and none of these are heated/cooled.

Based on everyone's feedback I sense double glazing is the way to go but considering the lack of ceiling insulation and the fact that the majority of rooms are not heated would I be better off with a mixed glazing solution.

Would this be something to consider?

- standard 6mm toughened glazing in the majority of areas of the house which are not heated/cooled and receive no direct sun.

- double glazing in the main living/kitchen space downstairs which does receive some direct sun and is heated/cooled

- double glazing in all the upstairs rooms as these receive direct winter sun and I want to retain winter heat gain.

Also, does anyone have any experience on using low-e glass in DG units that receive direct sunlight? I have heard that the low-e sheet has a blue glow so perhaps low-e should only be used on the south side?

Posted Monday 10 Aug 2015 @ 11:37:28 am from IP #
Catopsilia
Member

Hi, woobar
That wide north veranda: is it important for the aesthetics of the house?
It seems to me that the veranda is a primary cause of your problem in keeping warm. Could you move it around to the south side?

By the way, my low-E glass (which is in direct sunlight) looks exactly the same as plain glass.

Posted Thursday 13 Aug 2015 @ 12:36:57 am from IP #
KarenS
Member

Had a uPVC casement 4-10-4 Argon Low-E in a completely exposed west-facing wall in Melb. Looking through it, very SLIGHTLY darker than original single glazed (3mm) windows, but in those particular circuimstances, it was actually a benefit, as it seemed to remove a little bit of the dreadful glare we used to get. The particular window was a fair b*****d, and I am glad I don't live in that house any more. The d-g improved the window about 2000% - FAR less outward heat-leak in winter, good in summer with canvas (100% blockout) blind down on filthy hot afternoons, and it let in a noticeable amount of heat in sun in the winter. So as long as I "worked" it, it was great, for a wretched window which should never have been there in the first place,..

Posted Thursday 3 Sep 2015 @ 11:53:56 am from IP #
Morbo
Member

if its just to keep the kids in on 2nd floor, just lock the sliders?
There is not many single storey houses in the old world, but there is no epidemic of kids marching through windows and killing themselves.
Is mankinds IQ declining, do we need natural selection? Or are people just weak?

Plus if your house is build to BCA it should be impossible to fall from a window until the kids are out of monkey stage. I.e. 1m high sills and no other way to climb there.

Posted Friday 4 Sep 2015 @ 10:20:30 pm from IP #

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