A question about describing triple glazed units

[ProDave]

We have Rationel triple glazed doors and windows.

Most of them are 4,20,4,20,4 which I understand.

The doors however, and one of the larger windows, have toughened glass on the inside, and the make up of those is described as 4,20,4,18,6,4

Now I understand that means the inner pane is thicker and is toughened glass, and hence to keep the same overall thickness, the "inner" gap is 18mm instead of 20mm.

But the bit that confuses me is the 6,4 at the end. Does that mean 6.4 (six point 4) mm thick toughened glass? or does it mean something else?

I am asking because one window, the landing Window, we want a stained glass unit in that. Because Rationel don't do stained glass, we have bought that window unglazed and are looking for someone to make up the triple glazed unit for it with the middle pane being stained glass.  Because it will be quite low on the half landing, I think it also needs to be toughend glass on the inner pane. So I am trying to understand just what we need to specify.

[Jeremy Harris]

Ours have 6.4mm thick toughened glass on the inner pane, and the same reduction in gap, so my guess is that 6.4mm might be a standard thickness for toughened glass (but I've not checked).

[Rattyjohn]

From my railway coach building days, 6.4mm was the standard thickness of laminated glass (two 3mm sheets either side of a 0.4mm interlayer). As far as I know toughened glass comes in thicknesses to the exact millimetre, 3,4 and 6mm being the most common sizes. If your glass is 6.4mm then it's almost certainly laminated, which to be honest is preferable to toughened in a domestic situation.

[Jeremy Harris]

It may well be laminated - I'll try and read the markings and report back.

[PeterW]

1 hour ago, ProDave said:

I am asking because one window, the landing Window, we want a stained glass unit in that. Because Rationel don't do stained glass, we have bought that window unglazed and are looking for someone to make up the triple glazed unit for it with the middle pane being stained glass.  Because it will be quite low on the half landing, I think it also needs to be toughend glass on the inner pane. So I am trying to understand just what we need to specify.

You will struggle to get a true leaded stained glass triple glazed unit. 

Glass used for stained work tends to be 3mm and the lead cames are 5mm ish - this gives you an uneven finish to the leaded panel that won't fit into ordinary warm spacers without a lot of work. Leaded glass also leaks in the cames so it won't properly seal between the inner and outer - it becomes a big double glazed unit with an inner panel.

What you may be better off doing is having the leaded panel bonded to the middle pane - using 3mm it works fine and you can use epoxy on the edges to hold it. The inner pane is added and the unit sealed. That allows you to have whatever you want in the unit but without the hassle 

[AliG]

That's the glass I have ordered up Dave, it is 6.4mm laminated glass which is exactly as John describes it. Some manufacturers use 6.8mm laminated glass which has a thicker layer of plastic in the middle.

I would expect a triple glazed stained glass window to have 4mm toughened either side of the stained panel, although this may only be strictly necessary if the window needs to be safety glass for building regs, this is the normal make up for a triple glazed window.

The 6.4mm laminated glass is a lot harder for burglars to get through. It also improves sound transmission as the different thicknesses of glass have different resonance properties.

[ProDave]

I guess the important thing is the overall thickness of the unit must be 52mm as that is what the window is built for.

I will have to check building regs, but the bottom of the window will only be about 300mm above the floor of the half landing, so I would expect it to require toughened glass, and probably a handrail across the window opening? (if it does need a handrail that will be made "portable")