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Fixed Skylight What Glazing?

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#1 Auchlossen



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Posted 12 February 2016 - 09:14 AM

I have a simple fixed, ie non-opening, skylight planned in a nearly-flat roof, size 3m x 1.5->>0.75m ['triangular']
  • externally Insulated upstands,
  • upstands with slope for runoff,
  • top layer of triple glazing larger than the outside measure of the upstand
  • bottom layers to be smaller than inside measurement to sit inside also on gasket.
  • glazing gaskets for glass to sit on
What spec for glazing?
  • 4mm glass?
  • low-E glass on which layers? outer face of inner pane
  • spacing? 3G windows usually have 4-8-4-8-4, but 4-16-4-16-4 might be better
  • U-values?
  • is safety glass necessary/better for ?outer layer
Look forward to your advice :)

#2 cjard


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Posted 12 February 2016 - 07:28 PM

probably 6mm or 6.4mm for glass that is touchable, maybe thicker, toughened outer, lami inner. don't know if your glazier will do 4mm at the size you're after

glazier will recommend which faces to low e. if you change their spec they may say yooure on your own if the unit shatters

ask your bar supplier if 3g is possible; it wasn't for me at a 6-16-6-16-6.4 due to lack of space in the profile

#3 joiner


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Posted 12 February 2016 - 07:39 PM

Play around with this...


#4 jsharris


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Posted 13 February 2016 - 12:29 PM

As heat loss is going to be slightly greater through a roof light than through a vertical window, then I'd go for better glazing than the standard 4-16-4-16-4 arrangement. All our windows are 4-20-4-20-4, argon filled, with double low e coating, one of the inner face of the outer pane, one on the inner face of the middle pane (the normal spec). Probably also worth looking at using glass with a lower overall IR transmission, too, to allow light in but limit solar gain.

Unless the glass is likely to be subjected to any unusual impact loads I can't see the need to go for 6mm, or toughened glass, unless it's in a location where the regs require it. PV panels seem to do just fine with a single layer of non-toughened low iron 4mm glass.

#5 doofaloofa


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Posted 13 February 2016 - 07:20 PM

If the roof is nearly horizontal it means folk will likely walk upon it at some point

Thus prudence would suggest the external pane should be strong enough to stand on

Triple glazed with external pane toughened