Distorted reflections on window glass

[Lulusun]

I’ve ordered grade A double glazed windows and the way light and other objects, like overhead cables, reflect off the glass gives the impression that it is warped or wavy. For example the straight cables look like they bend in two directions. The neighbours windows don’t have this but there are some other houses I’ve noticed that have similar warped-looking windows. My windows contractor tried a different glass which was slightly better but still has the same issue. The contractor is saying this is a property of the newer glass offering more heat protection. He said it may also be related to the position if the windows. Is this true or is it just poor quality glass?
It’s very unpleasant to look at and I’m trying to find a solution but my windows contractor is saying there is not much else that can be done.
Pictures attached.

 

[Harry Bloomfield]

For example the straight cables look like they bend in two directions.

The apparent distortion, is due to the pressure/vacuum between the two panels of glass. When they were made, they will have been made at whatever the atmospheric pressure was at the time, once sealed, if the atmospheric pressure rises, they distort to bow in, if the pressure is less, they will bow out. Atmospheric pressure, varies contantly.

 

[Lulusun]

The apparent distortion, is due to the pressure/vacuum between the two panels of glass. When they were made, they will have been made at whatever the atmospheric pressure was at the time, once sealed, if the atmospheric pressure rises, they distort to bow in, if the pressure is less, they will bow out. Atmospheric pressure, varies contantly.

Thanks Harry. But how does that explain the majority of neighbours’ and my own current house windows not looking distorted? Wouldn’t all double-glazed windows suffer if that were the main cause of the distortion?

 

[Harry Bloomfield]

Thanks Harry. But how does that explain the majority of neighbours’ and my own current house windows not looking distorted? Wouldn’t all double-glazed windows suffer if that were the main cause of the distortion?

As I said - the atmospheric pressure at the time they are sealed, decides whether they are concave, or convex in the current atmosphere. When the current atmospheric pressure matches that of when they were sealed - they will be flat/ no distortion.

 

[Notch7]

I’ve ordered grade A double glazed windows and the way light and other objects, like overhead cables, reflect off the glass gives the impression that it is warped or wavy. For example the straight cables look like they bend in two directions. The neighbours windows don’t have this but there are some other houses I’ve noticed that have similar warped-looking windows. My windows contractor tried a different glass which was slightly better but still has the same issue. The contractor is saying this is a property of the newer glass offering more heat protection. He said it may also be related to the position if the windows. Is this true or is it just poor quality glass?
It’s very unpleasant to look at and I’m trying to find a solution but my windows contractor is saying there is not much else that can be done.
Pictures attached.

is the glass toughened - the heating process can warp glass and toughened glass is often not flat.

The low emissivity coating has a very short shelf life and can get easily damaged - if It’s touched before assembly it can show weird marks - the image with the protection tape still on the frame might be showing this effect.

please note low e coating are positioned on the inside of the double glazing, on face 3 counting from outside



I would guess your glass is a soft coat low e coating on the internal pane and low iron glass on the outside - it’s probably not possible to see which glass is causing the problem - maybe shining a torch at different angles might help show what’s going on.



In my experience float glass only gets a bit floppy when the pane is pretty big - over say 900 x 900.

Its true that large DGU units can have glass that is not flat - they usually present as a bit concave - if you have a straight edge you can check for this with a set of feeler gauges.

 

[crank39]

@ronniecabers, over to you Ronnie, this is your area

 

[opps]

The apparent distortion, is due to the pressure/vacuum between the two panels of glass. When they were made, they will have been made at whatever the atmospheric pressure was at the time, once sealed, if the atmospheric pressure rises, they distort to bow in, if the pressure is less, they will bow out. Atmospheric pressure, varies contantly.

Double glazed units that have a vacuum?

 

[Lulusun]

is the glass toughened - the heating process can warp glass and toughened glass is often not flat.

The low emissivity coating has a very short shelf life and can get easily damaged - if It’s touched before assembly it can show weird marks - the image with the protection tape still on the frame might be showing this effect.

please note low e coating are positioned on the inside of the double glazing, on face 3 counting from outside



I would guess your glass is a soft coat low e coating on the internal pane and low iron glass on the outside - it’s probably not possible to see which glass is causing the problem - maybe shining a torch at different angles might help show what’s going on.



In my experience float glass only gets a bit floppy when the pane is pretty big - over say 900 x 900.

Its true that large DGU units can have glass that is not flat - they usually present as a bit concave - if you have a straight edge you can check for this with a set of feeler gauges.

Hello, thanks for the response. The glass is not toughened, but the inside glass has a low-e coating as you were saying.

So are you saying this is a fault of the glass and that it’s not supposed to look like this? Is this likely a fault of the batch or do you think it’s normal for low-e glass?

 

[RandomGrinch]

Double glazed units that have a vacuum?

Rare and costly...

What is Vacuum Double Glazing? - Vacuum Glazing UK

What is vacuum double glazing? We explain how vacuum glass works and why you need it in your home.

vacuumglazing.co.uk

 

[crank39]

Although it exists I'll stick my neck out and say 99% of installations don't use vacuum insulated units, also something the manufacturer doesn't and won't tell you is the seal that forms a 'sealed unit' is actually permeable, if it lets argon escape within 4 years it will also allow air in

 

[Lulusun]

Although it exists I'll stick my neck out and say 99% of installations don't use vacuum insulated units, also something the manufacturer doesn't and won't tell you is the seal that forms a 'sealed unit' is actually permeable, if it lets argon escape within 4 years it will also allow air in

These are argon filled windows. Any opinions on why the glass looks distorted? Is this normal? How can I get low-e glass that does not look distorted or wavy, like in the pictures?

 

[crank39]

I don't think you ever will if I'm honest

 

[Lulusun]

I don't think you ever will if I'm honest

So in your experience, the higher the “Low-e” rating, the more distortions? Is there a grade at which these distortions are no longer seen or are negligible?

 

[crank39]

I don't think it has anything to do with the Low e coating or A rating, it could be how the glass has been floated, how it's been toughened if it is actually toughened or simply because of the manufacturing process, like I say I'm not an expert on glass unit manufacture

 

[^woody^]

Have a search for Sheet 4.10 from the Glass and Glazing Federation. This details the specification for visual quality and the common issues and acceptability of them.

That last image does look particularly bad and unacceptable. I've seen better sheets of plastic on bus shelters.