One of the decisions I kind of regret most about my conversion was that I retained the look of the original south facing industrial size roof glazing, basically by swapping all the original single pane roof lights for double glazed ones. It makes for a lovely view, but last summer the temperature in the room below it was 45 degrees.

I had some good results just hanging a length of tyvek airguard vapour barrier (looks like roof felt with one metallised side) under it to see how much of the heat would reflect away - probably a reasonable amount, though the 150mm deep anthracite grey roof bars (12 in total) that support the glazing certainly diminish the effectiveness

Installing something, maybe a grille with long horizontal slats to behave like a stack of mini brise-soleil would probably be the best solution so that I still get winter sun and can see out, but I'm not quite in a position to have something fabricated and fitted

So, thinking on the relative success of the inner reflective membrane I purchased some solar window film

I've applied it to one pane as a test and all looks good but I'm slightly concerned that the inner pane of the filmed window is now so hot (it's been applied for an hour) I can't keep my hand in contact with it. In contrast the pane next to it is warm but cooler than I am.

I've tried to find some info about the maximum temperatures of DG units/maximum temperature differentials between faces (I'd estimate this was 55 inner, 25 outer today) to avoid causing problems for the sealant at the sides etc but haven't so far succeeded..

Any ideas if installing a solar control film on the inside of a double glazed unit would cause problems/premature failure of the unit?

Posted By: cjardlast summer the temperature in the room below it was 45 degrees

'Maximum temperature for a double glazing unit' ?

Difficult to tell, until it breaks !

I have read of 6-layer laminated glass surviving regular 120°C (laboratory use)
and another user who made his own DG that siurvived 170°C before suddenly yielding.

If you are lucky and your glazing has a decent perimeter gap, it might be OK...

Laminated and/or annealed glass will probably accept more heat than plain thick glass...

As I understand it, it is not 'the maximum' that does the damage, but the differential between the two panes.

I have one in front of my (black) garage door that has stood 32°C (int) and and is still intact ! I suspect that a contributing factor is that the frame is aluminium and has no thermal break.

Per rererenced link, the maximum temperature supported by a DG unit depends on several criteria such as glass type, frame type, amount of shading, type of fit (clearances and spacers) - breakage will likely occur when the glass contacts the frame...

https://www.windowsonlineuk.co.uk/blog/causes-double-glazing-crack/

The solution might be to leave the glass alone, hope it is not getting differential thermally stressed, and fit a (reversible) multi-speed ceiling fan.

Or a ducted fan to mitigate the stack effect (by pulling heat downstairs into a cold basement for example).

gg

As I recall 43-47C is about as hot as you can touch by hand. So if it's 15C outside the temperature difference is around 45-15=30C.

I guess you might get -10C outside and 20C inside in winter which is also 30C.

<blockquote><cite>Posted By: Simon Still</cite><blockquote><cite>Posted By: vivienz</cite>
The solar control films do seem to work, but they are expensive and look like a giant version of mirrored sunglasses from the outside and give a distinct blue tint from the inside. An acquaintance who applied some to a large window of his house commented that, in the end, it was only a little less expensive than sage glass (sp?) which is very expensive.</blockquote>

The stuff I fitted to the double glazed windows of a c2014 completed new build flat I lived in with an entirely south facing aspect was definitely meant to be fitted to the inside.

Not least, I think it would get quickly scratched when cleaned if used on the outer face.

They had quite a few different gain reduction levels - more gain reduction, more mirrored appearance and darker tint. Ours was the least and still made a significant difference. From the outside it didn't look very mirrored but that the same time enough to stop you being able to see in during daylight hours at least (and you could tell it was different to the windows in the flats to either side.

is still in place and units haven't failed yet....</blockquote>

Good to know! Do you have the details of the product? We have an east facing guest bedroom that gets hellishly hot in the mornings and I've been considering some sort of shading. It's a gabled window and so is tricky to fit blinds, etc. and I don't fancy trying to fit curtains, either. Something applied to the glass may be the way to go.