Fixed vs openable rooflights

[Gone West]

2 hours ago, Adsibob said:

Thanks @PeterStarck. Where are your 3G sliding doors from?

There're Rehau lift slide triple glazed doors.

Edited January 19, 2021 by PeterStarck

[Adsibob]

On 18/01/2021 at 19:46, Dan F said:

 

You might need to find a different supplier!  A good solar-glass is near enough transparent and will let almost as much light through as standard glass while reducing the solar gain.

 

There may be other manufactuers available also, but this is the moslty commonly used stuff AFAIK: https://www.saint-gobain-glass.com/products/cool-lite-skn

 

Looking at the spec (when made up in double-glazing) this is what you are looking at:

- The 0.39 g version give 65% solar gain for 96% of light.

- The 0.36 g version give 60% solar gain for 84% of light.

- The 0.32 g version give 53% solar gain for 74% of light.

 

@Dan F this is helpful thanks. The supplier of some other windows, all double glazed (rear elevation at first and second floor, all west facing) is offering Sunguard SN 70/35 which he tells me comes with a coloured tint. I attach the specs, which if I am reading correctly show the g value of this glass is 0.348 which is between the 0.36g and 0.32g figure that Saint Gobain offers in the link you provided above. What is a little concerning, is that it looks like with the Saint Gobain one would have 84% of light if one when with their 0.36g glass, whereas with the Sunguard SN 70/35 transmittance is 70%. That strikes me as quite a difference, or am I focusing too much on this?  The Sunguard SN 70/35 also has a slightly better U value at 1.0 vs the 1.1 of their standard glass option which is Climaguard A 1.0.  

 

The coloured tint is probably more of an issue for me. The colour rendering index of the SN 70/35 is stated as 94.0, vs their standard (Climaguard A 1.0) which has a colour rendering index of 98.0 with a g value of 0.55. Interestingly the transmittance is the same, at 70%. I attach the Climaguard A  1.0 spec as well.

 

This supplier seems fairly flexible and has said there is no additional charge for switching from Climaguard A 1.0 to Sunguard SN 70/35, but that if I wanted something else there would be.  He's also offered to bring samples of both Climaguard A 1.0 and Sunguard SN 70/35 when he does the survey, but this would be after i sign a contract and pay a deposit. I googled colour rendering index to see if I could see online the difference between 94 and 98, but clearly that would be testing the possibilities of remote learning beyond the possible. I couldn't find much other than to suggest that with both close to 100, they would produce quite close representations of the actual colours seen through the glass, with 98 obviously being more accurate, although if the rendering scale is logarithmic, then a 4 point difference could be quite massive

 

If anyone has experience of this and can help me solve the conundrum before I have to sign the contract, that would be much appreciated!

[Dan F]

@Adsibob Sorry, I confused you with my numbers!

 

That 84% I quoted was as compared to Planitherm XN glass (which has light transmittence of 81% and solar factor of 0.6).    If you look at the actual figures, the guardian solar glass actually seems to be marginally better than the Saint Gobain.  See: https://www.saint-gobain-glass.com/products/cool-lite-skn

 

The glass will be slightly tinted as a result of the coating yes, but that's rather different to a "tinted glass" which has been tinted deliberately to achieve a colour, like the ones in the document you attached previously.  The web page gives you an idea of what it might look like externally and internally:  https://www.guardianglass.com/gb/en/products/brands/sunguard/super-neutral/70-35

 

It's hard to compare the u-values as each manufactuer uses different thicknesses of glass/argon in their calculations, I woulnd't expext any significnat differences though.

 

Not sure on the specifics, but I'd hazard a guess that guardian are probably number #2 in europe size-wise and as good as Saint Gobain.   @craig would know...

 

Didn't look at CRI when we chose glass, so not sure there, but it may be more important for solar control glass I guess, which we didn't use.  Saint Gobain don't seem to uote this though, so can't compare.   Obviously 98 is better than 94, but you can't get the reduced solar gain with no any other impact.  End of the day, if you need the solar glass you get it, if you don't then you use climaguard which will mean i) no tint, ii) marginally better colours iii) more solar gain (beneficial in in winter, potentially issue in summer)

 

 

 

Edited January 23, 2021 by Dan F