Apart from cost, any downside in using toughened glass?

Is there any disadvantage in changing all the window glass to toughened?

A lot of my windows are toughened glass and I've been offered an upgrade to all remaining (non toughened) windows to toughened glass for $2500. In the long run I think I'll come out on top since there is a much less chance of breakage with the associated costs and inconvenience.

However, is there any downside in using toughened when I don't need to?

Yes Casa, the downside is $2,500 - that's a whopping price for converting annealed glass to toughened - tell them I said so. Toughened glass is stronger - but it can shatter if a bird was to fly into it. Never clean toughened glass with a scraper or razor blade as it can easily be scratched. It will have a wavy appearance in reflected light.


Ed

Thanks Ed,

Will toughened glass look wavy if looking through it? I'm not too worried about reflected light.

When you say it can shatter if bird was to fly into it, does that mean in this case it more easily shatters than normal glass? Or is it that if a bird was to fly into either glass type it would shatter.

Surprised to hear that toughened glass scratches more easily than untoughened glass.

Cheers,
Casa

You're welcome,

It won't look wavy through the glass. 5mm is better than 4mm.

A sharp blow can shatter it, but it will withstand a lot more weight.

Toughened glass has "fines" in the surface which can be picked up on a scraper and scratch the glass.

Ed

This toughened glass business is quite complicated. So far I know:
1) Toughened glass scratches easier than normal glass
2) Toughened glass reflections can look wavy, but looking through them is the same as normal glass
3) Toughened glass can withstand more weight

The bit I don't know is whether toughened glass is tougher under all situations. That is, is a sharp blow more likely to break it than it would normal glass? What's the relative breakage likelihood under different situations?

And finally Ed, the catch all question. If you could have either normal or toughened glass in all your windows in your home, which would you choose?

Cheers,
Casa

Hi Casa

A blow from a sharp object that can shatter toughened glass would not break annealed glass.

Yes, I would have toughened over annealed as it will take more pressure before it breaks and it does break it goes into very small (safer) pieces.

Ed

Can i ask why you would change it in the first place? Unless its in a safety compromized area (ie less than 600mm from the floor)

It has no better sound proofing or thermal properties than regular float glass?

Hi Dannopower,

The reason I was considering toughened glass is reduced breakages in the future. Although a window is rarely broken, if there is a signifiant reduction in the chance of a breakage there would be two advantages:
1) Less inconvenience of getting broken glass fixed (saves my time)
2 Less long-term cost as spending some money now would result in less "maintenacne" costs later (saves my money)

It's also nice to know that it is safer. It looked as if toughened was an all round winner, except for up-front cost. But now I hear it scratches more readily and is more easily shattered in some situations. These two tend to negate the long-term cost benefit. Toughened glass is not looking now be the all round winner I though it was a couple of days ago.

So it looks like six of one and half a dozen of the other. Still tending slightly towards toughened, but I could go either way. Now where's that coin ...

Cheers,
Casa

I found your coin Casa it was a $2,500 double header... I say tails.

At no cost I say heads...

Ed

Dear Casa,

I don't think that scratching of the glass is a major issue when the units are handled with care. Toughened glass also performs better in situations were the glass heats up unevenly - thermal stress related glass breakage.

We only use toughened glass were either the building code requires it, the thermal stress breakage might require it, extra safety for children and surely for bushfire areas. Each project is different in regard to shading and other aspects. A general answer might not solve your problem. I think in ordinary applications there is no necessity for toughened glass. My question is did you ever consider double glazing The thermal comfort you will gain from that is worth considering if that is not already part of your plans.

Best regards
Kris

Hi Kris,

Thanks for your input. All my windows are double glazed.

You mentioned that scratching of the glass is not a major issue when the units are handled with care. I can do that, but my kids (and whoever gets the house after I'm gone) may be less careful. I guess I want the glass type that will give me the least worries going forward - set and forget, if you know what I mean.

Cheers,
Casa

Dear Casa,

I checked with Viridian Glass and it is correct that toughened glass is a little bit easier to be scratched, but in saying that all glazing can be scratched anyways. So care is important no matter what.
Especially when you are talking about kids I would probably go for toughened glass due to the safety aspect of the product. It shatters in small granules instead of big pieces. Meaning the risk of cuts and other injuries is reduced to a minimum. That’s why toughened glass is required for all floor level windows and for doors.

It’s up to you but I would much rather live with a scratch on my window than with a scratch on my kid.

All the best with your project.
Kris

Thanks Kris,

I'm still thinking about this one (and the 200 hundred other decisons I need to make), but I'm steering towrds toughened glass.

Cheers,
Casa

Hi,

have you thought about laminated glass ? The one pane which is more likely to be scratched anyway. It is also more soundproof and quite burglar resistant.
I don't know about Australia but the over here the price for laminated glass is pretty much the same or sometimes even less than toughened glass.

My windows are double glazed and quite large (2 m x 2.7 m in some cases), so the weight will be quite high. Laminated glass seems to come in thicker sheets and therefore the weight would go up. Also, the frame pocket varies from 16 mm for the sliding windows up to 24 mm for the fixed windows. If I went for laminated glass in the sliding windows the already too small air gap of 8 mm would be even smaller!

So, maybe I've got my thinking wrong, but laminated glass seems like a step in the wrong direction.

8mmm air gap is not really a preferable double glazing unit. Laminated glass has the advantage that cuts out 99% of the UV plus it has a better noise insulation value. There is also an special version of the lam that is manufactured for noise reduction purposes. In IGUs (Double Glazing) it is important to keep a 30% difference of thickness in the two glass panes to achieve best results in regard to noise reduction.
In regard to stepping up the forced entry barrier laminated glass is definitely preferable.

The weight shouldn't be an issue after installation at least when you have the right window and door hardware components. Weight is he worst argument when compromising on comfort or security. The air gap of 8mm or less with laminated would drive my decision here. As we are talking changing of glass there is probably not much you can do about it if you don’t decide to go with the system that allows for this alterations while maintaining an air gap +10mm.

Best regards
Kris

Thanks Kris,

UV reduction: not important
Noise insulation: not imporant
Forced entry: This would be nice, but only for a small number of windows at the front at ground level
Weight: Important, as I imagine 150 kg can be handles by four people, but once you get much above this I'll need a crane $$$$$
Air gap: Very important. Like you, I'm not happy with 8 mm, but going any smaller would be a disaster. Maybe I'll get argon put into the 8 mm gap windows (the sliding windows), but then only if it can be done for no more than about $50 per window.

Argon should be possible soon for less than 50$ if you have the right supplier. Please keep in mind it's still glass after all. Not knowing you system the security risk could also be the locking and not the glass.

If you should take laminated the UV reduction is a nice extra that safe your furniture from fading and helps to reduce the UV impact on the eyes.

Argon gas can improve a unit performance by around 10% depending on the glazing type. I have seen researches that suggest that argon works better with 14mm air gap instead of 12mm air gap. Not quite sure what that means for a unit of 8mm or less.

Weight: Is hard to say, depending on accessibility of your building it is possible to work with higher weights. We regularly end up supplying unit of 200kg plus that are handled without a crane. Double Glazing causes more weight but it will pay of in living comfort, so it's worth the effort.

If by this you mean the extra for Argon, it should be less than $10/m2.

Ed

Beauty. My sliding windows are just under 4 m2 each, so I'll be able to upgrade each of the 9 sliding windows for less than $50 each. This should bring the 8 mm gap for the sliding windows up to the same thermal performance as the other windowes which have a 12 mm air gap (from the graph you provided Ed).

It's all coming together

Thanks for your help Ed, Kris, windowexpert, et al.