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14447 posts

Uber Geek
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  Reply # 1251743 5-Mar-2015 15:15
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Fred99: 

I won't argue about the advantages of double glazing, but there is one serious disadvantage.  The units have a finite life - as my next door neighbour has found out, a $25k cost to replace all double-glazed units about 20 years old - many were failing (internal condensation).  A conventional window lifespan is indefinite - subject to maintenance of the frame etc.  So the final calculation may not be as simple as subtracting energy cost saved over the additional cost of double glazing, though there is an intangible comfort factor (incl reduced noise).
If building or renovating - I'd be asking a lot of questions about durability/lifespan of the various systems available before stumping up with a serious amount of cash.  I'm not sure about the double glazed panels themselves, but there are some very dodgy operators (and no doubt many very good ones too) in the double-glazing/aluminium joinery business.


That is interesting, and not something you hear much about, and not something the windows companies tell you about. Do you know if laminated glass lasts much longer? Under the NZBC I believe regular non structural windows only have to have a life of 15 years, which isn't long at all. I think it  should be 25.  Insulated glazing units though should last longer than 20 years, but I guess it depends on the quality of them, and the exposure of them to the elements and sun. I am guessing sun could perish the seal between the pieces of glass. I would hope the technology today is better than that used 20 years ago.   If people really want good performance, triple glazing is excellent, but not sure how much it is used in NZ.  Replacing sealants and seals is a huge business, which is where conventional lap joints have the advantage in terms of longevity,

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  Reply # 1251825 5-Mar-2015 17:10
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mattwnz:
Fred99: 

I won't argue about the advantages of double glazing, but there is one serious disadvantage.  The units have a finite life - as my next door neighbour has found out, a $25k cost to replace all double-glazed units about 20 years old - many were failing (internal condensation).  A conventional window lifespan is indefinite - subject to maintenance of the frame etc.  So the final calculation may not be as simple as subtracting energy cost saved over the additional cost of double glazing, though there is an intangible comfort factor (incl reduced noise).
If building or renovating - I'd be asking a lot of questions about durability/lifespan of the various systems available before stumping up with a serious amount of cash.  I'm not sure about the double glazed panels themselves, but there are some very dodgy operators (and no doubt many very good ones too) in the double-glazing/aluminium joinery business.


That is interesting, and not something you hear much about, and not something the windows companies tell you about. Do you know if laminated glass lasts much longer? Under the NZBC I believe regular non structural windows only have to have a life of 15 years, which isn't long at all. I think it  should be 25.  Insulated glazing units though should last longer than 20 years, but I guess it depends on the quality of them, and the exposure of them to the elements and sun. I am guessing sun could perish the seal between the pieces of glass. I would hope the technology today is better than that used 20 years ago.   If people really want good performance, triple glazing is excellent, but not sure how much it is used in NZ.  Replacing sealants and seals is a huge business, which is where conventional lap joints have the advantage in terms of longevity,


I doubt that some of them (double-glazing industry) want to talk about it much.  There's a somewhat political article here:
http://www.askjeff.co.uk/double-glazing-is-not-so-amazing/
This mentions quality of product and install.  As I said, there are some dodgy operators in the business here.  If you're not dealing with one of the reputable larger firms, google the directors and staff of the company you're dealing with - and be prepared for surprises, hits to "Fair Go" and prosecutions for dodgy sales and service in other areas of the building trade.  One visited me - a builder working next door popped over when they left - and gave me a heads up warning to not deal with them.


Good question about laminated glass lifespan.  One glazier was telling me that the laminated glass also acted as UV cut.  My limited knowledge of polymers includes a rule of thumb that if the polymer is transparent to UV, then it's less likely to break down in UV, so I'm not sure if I believe what the glazier was saying. Laminated car windscreens can show some breakdown / whitening of the laminate after a couple of decades, but from what I've seen that seems to be from the edges, and perhaps moisture (or other atmospheric) cause.



 
 
 
 


434 posts

Ultimate Geek
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  Reply # 1251883 5-Mar-2015 18:40
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Interesting article - I have a friend who had some double glazing  roof windows put in about 10 years ago - 2 of 3 of  those now have permanent condensation. 

I'm not changing the width of the opening - but want to change a window to a sliding door - not sure if that will require double glazing or not. But am certainly going to do some more research 




I help authors publish their books - DIYPublishing.co.nz

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  Reply # 1251959 5-Mar-2015 22:01
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lissie: Interesting article - I have a friend who had some double glazing  roof windows put in about 10 years ago - 2 of 3 of  those now have permanent condensation. 

I'm not changing the width of the opening - but want to change a window to a sliding door - not sure if that will require double glazing or not. But am certainly going to do some more research 


I installed two new french doors to replace a (single glazed) window unit the same width.  The work did not in itself need building consent as it was non-structural - the existing lintel spanned the width of the new doors.  However, as this was part of other work on the plans which did require consent, and it did need to meet code, then there wasn't much option.
So strictly speaking, if the glass area increases, you probably need to double glaze  (you would in Chch / Si anyway).  But because the work is consent exempt, there's nobody checking.  OTOH, even if exempt, the work should still meet code.  OTOH again, if in future it became an issue (very unlikely IMO), as there's no documentation trail, you could "not recall" when the change was made. Politicians get away with that all the time.

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  Reply # 1252202 6-Mar-2015 11:36
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Fred99:
lissie: Interesting article - I have a friend who had some double glazing  roof windows put in about 10 years ago - 2 of 3 of  those now have permanent condensation. 

I'm not changing the width of the opening - but want to change a window to a sliding door - not sure if that will require double glazing or not. But am certainly going to do some more research 


I installed two new french doors to replace a (single glazed) window unit the same width.  The work did not in itself need building consent as it was non-structural - the existing lintel spanned the width of the new doors.  However, as this was part of other work on the plans which did require consent, and it did need to meet code, then there wasn't much option.
So strictly speaking, if the glass area increases, you probably need to double glaze  (you would in Chch / Si anyway).  But because the work is consent exempt, there's nobody checking.  OTOH, even if exempt, the work should still meet code.  OTOH again, if in future it became an issue (very unlikely IMO), as there's no documentation trail, you could "not recall" when the change was made. Politicians get away with that all the time.
 

LMAO - we are also doing a deck which doesn't need a consent (only about 0.8m off  the gorund) - so hear what you are saying will act (or not) as you suggest. We will never sell this house  so I'm not worried about  Council records so much . 




I help authors publish their books - DIYPublishing.co.nz

203 posts

Master Geek
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  Reply # 1252985 7-Mar-2015 20:36
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I work for a aluminium company.

Double glazing is NOT require if you are replacing like for like, OR dont require a consent (as above mentioned, keeping existing lintel is a simple way of telling) Changing the layout or framing type doesn't affect this
ie changing from slider to bifold, or a 'wide' profile to a 'narrow' profile giving more actually glass area. (again, lintel / structural framing must stays the same) 

The law regarding new sliding doors glass type: (single or double glazed)
1) if it has full height glass - it MUST be safety glass
2) if it has a vision rail about 80cm or so up - it DOESN'T require safety glass, but must be at least 5mm thick (average clear window in a new house is 4mm)
It is cheaper to have a vision rail and 2 piece of glass then to pay for 1 large safety glass.
Regardless of consents, joinery company shouldn't sell anything other then this.
Of course it would be possible to have a vision rail and safety glass, this would be the most expensive option and not required.

We do this kinda of work, but are not in Auckland, but if you want I could give you a price when im back at work on monday for a sliding door that size (without install)

As a general rule, double glazing is required by law if building a new house - with a couple of exceptions, ie internal access garage can still be single glazed
There is also a lot of rules regarding safety glass, it depends on door type, if its a wet area, height from ground etc etc
All our double glazed panels have a 10 year warranty for defects (most commonly moisture inside)
I myself have been thinking of how long they are actually going to last. Double glazing has been law for about 7 years, if they last 20, in 13 years there is all of a sudden going to be a lot of foggy windows....
I know argon filled makes the panels last longer, but is more expensive

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