Triple glazing worth it

ComicGeek

Albermarle said:

ComicGeek said:

grumbler said:

grumbler said:

ComicGeek said:

...triple glazing blocks out more direct sunlight than standard double glazing, sometimes as much as 50% more.

It's very hard to believe that an extra sheet of clear glass can block even 50%, let alone more.

On second thought, if double glazing blocks, say, 4%, i.e. 2% per a pane, then I'd expect a third pain to block 2% too, i.e. 6% in total, 50% more. Not a big deal really.  50% of nothing is nothing.

Standard double glazing has a g-value of 0.73, ie 73% of the solar heat gain is allowed through the glass, 27% is blocked. Much, much higher than 4%!!

Triple glazing can have g-value down to 0.34, ie only 34% of the solar heat gain is allowed through, 66% is blocked.

Also, the frame of triple glazing units are normally thicker than double glazed, so the amount of glazing in a window is usually less, further reducing the window g-value.

Presume though it does not block 66% of the light though ( just the heat) ? The house would be a bit gloomy if it did !

Light transmission is closely linked to g-value for standard glass, very similar values, so a cheaper triple glazed unit without specialist glass could well block 66% of light transmission. A typical double glazed window would reduce light transmission by 30%. Manufacturers generally improve heat loss cheaply by upgrading the glass, which in turn reduces the g-value and light transmission - that's cheaper than designing better frames, or using better quality glass.

There is more specialist solar control glass that can reduce g-value without reducing light transmission, but that wouldn't be normally offered by standard window companies.

Martin_the_Unjust

It always used to be said triple glazing for sound insulation but double for heat insulation.

I don’t think it’s so true now though.

ThisIsWeird

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

EssexExile

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

And I've just opened my triple glazed window, I can see no difference in light level looking through the glass or around it.

ThisIsWeird

It's a transparency conspiracy!

Albermarle

ThisIsWeird said:

It's a transparency conspiracy!

I have done a bit of googling, although info on the subject seems a bit scarce. However it does seem that double glazing does reduce visible light transmission by at least 20%, and of course more with triple glazing, which is similar to what @ComicGeek said.
That does not mean necessarily that there is any distortion or translucency, it just means anything you look at through the double glazing, will be darker than not looking at it directly.
I guess that the difference may not be enough for the eye to be sensitive to it, or the brain adjusts, especially if there is no colour shift. It is probably more noticeable when light levels are already low ( or high) .
Also when you look in the garden for example, you are looking at a myriad of different surfaces and colours, so difficult to make exact comparisons.

ComicGeek

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

EssexExile said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

And I've just opened my triple glazed window, I can see no difference in light level looking through the glass or around it.

So with the window open, you really can't see a difference in colour tone through the glass when compared to the open view? It makes colours appear a little darker when viewed through the glass, perhaps some people are just more aware, it's very obvious to me. It doesn't make it fuzzy or less translucent, just makes the colours slightly darker.

I've also been in buildings where there is different glass on different elevations, and you can clearly see the difference from inside.

Nobbie1967

EssexExile said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

And I've just opened my triple glazed window, I can see no difference in light level looking through the glass or around it.

The human eye can see an amazing range of light levels varying by a factor of over a million, but as a result it is relatively poor as discerning relative light changes, so a 20-30% reduction is unlikely to be noticeable as you found. 

ThisIsWeird

ComicGeek said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

EssexExile said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

And I've just opened my triple glazed window, I can see no difference in light level looking through the glass or around it.

So with the window open, you really can't see a difference in colour tone through the glass when compared to the open view? It makes colours appear a little darker when viewed through the glass, perhaps some people are just more aware, it's very obvious to me. It doesn't make it fuzzy or less translucent, just makes the colours slightly darker.

I've also been in buildings where there is different glass on different elevations, and you can clearly see the difference from inside.

Will there be a difference that you can detect by comparing and open and a closed door or window? I'd suggest surely 'yes'. (Mind you, if the glass is at an angle to the viewing line, that's likely to have a greater effect, with reflections and stuff).
But I'm talking about everyday visibility. Am I aware that there's glass there? No. Sometimes I've even wondered if the doors have been opened by someone. It is just never an issue that you look through the three, or even five, sheets of glass and consider there's a reduction in clarity, light or visibility.
It just doesn't figure. 

ComicGeek

ThisIsWeird said:

ComicGeek said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

EssexExile said:

ThisIsWeird said:

Looking through 5 layers of glass this very second, it just doesn't occur to me that the light level or translucency is affected at all. 

And I've just opened my triple glazed window, I can see no difference in light level looking through the glass or around it.

So with the window open, you really can't see a difference in colour tone through the glass when compared to the open view? It makes colours appear a little darker when viewed through the glass, perhaps some people are just more aware, it's very obvious to me. It doesn't make it fuzzy or less translucent, just makes the colours slightly darker.

I've also been in buildings where there is different glass on different elevations, and you can clearly see the difference from inside.

Will there be a difference that you can detect by comparing and open and a closed door or window? I'd suggest surely 'yes'. (Mind you, if the glass is at an angle to the viewing line, that's likely to have a greater effect, with reflections and stuff).
But I'm talking about everyday visibility. Am I aware that there's glass there? No. Sometimes I've even wondered if the doors have been opened by someone. It is just never an issue that you look through the three, or even five, sheets of glass and consider there's a reduction in clarity, light or visibility.
It just doesn't figure. 

I get what you're saying, but you would notice when you have to put the lights on more, or the heating on more, after changing the glazing, due to the lower g-value and light transmission. Some people compensate for that by installing bigger and bigger windows/doors, but that also massively increases room heating loads.

When we do calculations for energy usage in new build
houses a double glazed window with high g-value and light transmission has a lower annual energy profile than a triple glazed window with lower g-value and lower light transmission, even if the U-value (heat loss) is much better. Just pointing out to the OP that you can't look at one value in isolation, and that in some (many?) cases spending the extra money on triple glazing will actually increase annual energy requirements, so a double hit in the wrong direction.