Triple Glazing

[Ken]

Think i am right in saying polycarbonate will go "milky" much more quickly and less clear

[AE-NMidlands]

Think i am right in saying polycarbonate will go "milky" much more quickly and less clear

but if it's the inside/indoor layer it won't be in the sun (i.e get any UV dosage)...

[openspaceman]

Think i am right in saying polycarbonate will go "milky" much more quickly and less clear

but if it's the inside/indoor layer it won't be in the sun (i.e get any UV dosage)...

That's right.

It's clear PVC that goes milky and brittle in my experience of the roof on my outhouse, such that I lashed out for corrugated polycarbonate for my log shed.

Having checked the acrylic is so cheap in 2mm that I'll go for that for the glazed passageway which is really only a roof-light.

Before I fitted double glazing I used the clear film that was fixed with double sided tape and then tautened with a hair dryer, it actually worked well on some windows that were never opened but was too fragile.

[Moxi]

I found this interesting and informative:



Moxi

[GarethC]

Interesting video (well for me at least), thanks for posting. I'd go as far as to say the thickness and material of the secondary glazing sheet makes very little difference thermally. It's all about the trapped layer or largely static air. Hence essentially cling film being really quite effective.

While polycarbonate is supposed to yellow over time due to UV, if used as secondary glazing it might be ok, as the glass filters at least some of the UV. Haven't seen a definitive answer to that question.

[Moxi]

Assembly shots at 58seconds but it is a good example of what that little extra layer of trapped air can achieve as its normally a lot colder in Maine than most areas of the UK.

Moxi

[wookey]

Yes, we have good triple glazing (Uw=0.78, Ug=0.52)) and it's brilliant, and I recommend 3G to everyone who is getting new windows. The extra cost is now small (~10-15% last time I checked), and they are a lot lower heat loss (new DG Uw=~1.4, 3G Uw=~0.8) . There is also a significant comfort gain due to warmer inner surfaces and very low noise transmission.

We had decent 2000-vintage double-glazing before (Uw=2.4ish) and we were planning to keep that on the south side, and maybe upgrade in another decade, but delivery costs (and the output of PHPP) were such that it made sense to do that whole house in one go whilst we doing the EWI and north-side windows.

The main disadvantages are that you can't tell what clothes to go out in without opening the door because internal temps are very consistent (this is the whole 3G+ good insulation + good airtightness combination). And when it's cold you get condensation on the outside rather than the inside, so you can't see out until it clears (and you can't just wipe it off so easily as it's on the wrong side).

The other really important thing to know when buying either 2G or 3G windows (or even just replacement units) is that you must specify warm-edge spacers and soft-coat IR as this makes a really big difference (~30%) to how efficient the glazing unit is for very little extra cost.