Hi,

I'm renovating a Georgian/Victorian house with an 8m x 4m west facing vinery - within the limits of making a glass room I'm trying to get the best thermal performance I can. Elsewhere I'm insulating walls, floors, roof well above part L1B to attempt to offset some of the inefficiency of this room.

My architect has specified 6mm-12mm argon fill-6mm double glazing and that's what all the replacement joinery has been manufactured and assembled to accept, she also specified Low E glass.

My understanding is that soft coat is measurably better in this application than hard coat (e.g. Pilkington Optitherm versus K on surface 3), but I'm getting significant resistance from the glazier - citing minimal thermal performance improvements and significant problems with manufacturing and handling.

I'm currently held up in everything by not having this room weather tight so I need to make an urgent decision if I should get another glazing company to quote.

I've (foolishly) lent my Green Building Bible to a friend. Can anyone give me definitive advice on how significant soft coat is vs. hard coat?

Many thanks

AMc

according to pilks, if I've transcribed correctly:

hardcoat - 6-12Ar-K6 gives a U of 1.63 (this is a centre of glass figure). light transmission 72%, energy transmission 68%.

softcoat - 6-12Ar-S6 gives a U of 1.28. light transmission 78%, energy transmission 59%.

your glaziers are old-fashioned / lazy. dump them. soft-coat is no prob.

I agree with Tom,

One of my biggest mistakes when I built was going with double-glazed instead of triples.

-Ralph

Warm-edge spacers, not aluminium ones. The edge loss due not only to frame but also ordinary spacers is very significant.

I agree that triple would be better, but the timber structure is complete. The capex roofing system is on site as are the sashes so the glazing sizes are now fixed at 24mm and it would be beyond my means to change them at this stage.

When I started out I had very little clue how significant the heat loss would be from this room, I know better now (thanks to GBBible and the magazine) but we're too far down the road. I'm hoping that the solid, insulated floor and exposed brick internal walls will make a positive contribition creating some thermal storage, again this is hope rather than design - I'll know better next time.

I have now had pricing back from the original glazier - Plikington K is around £2000+VAT, soft coat is Planitherm by Saint Gobain and £3000+VAT - seems way too much to me.

I'm now waiting on prices from 2 other companies for soft coat, one offers warm edge spacers and I've asked them both if they can do Krypton fill.

I'm sadly not surprised that parts of the glazing industry is so far behind the loop on thermal efficiency. As I've been managing my self build I've been stunned by the absence of interest in thermal performance or indeed environmental impact across the entire process. Most of the advice I've been given has been how to avoid the regs and save build costs, very disappointing.

Any further tips appreciated, many thanks for the suggestions so far.

Amc, not quite conventional, but how about thicker 3G units pretty well filling the rebates as made, and seeing about retaining them with glazing beads not fixed sideways into the rebate 'reveal', but somehow screw-fixed onto the sash's outside face? Assuming these are fixed lights, not sliding sashes or hinged, in which case the considerable extra weight of a 3rd pane cd cause problems.

Posted By: AMcI'm now waiting on prices from 2 other companies for soft coat, one offers warm edge spacers and I've asked them both if they can do Krypton fill.

I recommend against Krypton, unless you are limited in your sash width. If you have the space, Argon & a wider spacer bar is better.

-Ralph

the above price includes VAT by the way

All glazing south facing, Design of structure; heavy thermal mass, passive solar, (33% glass area)
soft or hard coat??? double or triple ??? Planning on external insulated shutters for use in winter

Been thinking this over for some time need help!!
thanks

Changing the glazing width isn't an option at this point (you live and learn) triple is too heavy for the woodern structure and without increasing the gap it's not going to make a massive difference as I understand it?
As we're replacing a single glazed Victorian vinery there are aesthetic compromises in how the roof is put together
The 6mm is necessary because of the size of some of the units - the largest being 60cm x 300cm.

A back of the envelope calc on glass size gives me about 50m2 (including some other smaller windows) so the price is about on the money - £4K inc VAT.

First alternative quote has come back £4K for K, £4.5K for soft coat both PLUS VAT- more money for no obvious benefit.
Second alternative is promised tomorrow morning.

I'm near Norwich UK if anyone has any suggestions for another supplier with a greener edge.

Thanks again, I'm really glad of your comments and suggestions.

Posted By: ralphd

Posted By: Mike GeorgeAny figures for that Tom? I have heavd percentage saving this and percentage saving that but have not seen hard data. I don't think the losses due to spacers are as significant as manufacturers would have us believe. Love to be proved wrong.

Ahh, there's your problem. You're asking a Brit when you should be asking a Canadian! ;-)
http://irc.nrc-cnrc.gc.ca/pubs/ctus/58_e.html

-Ralph

Thanks Ralph,

Not sure it justifies the use of warm edge spacers though. The improvements measured being more about the frame itself - unless I am missing something?

Quote Figure 5 shows the overall R-value for each window tested. In general, wood has a high thermal resistance and therefore the FR1 specimens performed best in terms of overall R-value. In fact, for all the specimens tested, the FR1 specimens had the best overall R-value regardless of which spacer bar was used; the only exceptions were spacer bars IG4 and IG6, where the R-values for FR2 specimens and FR1 specimens were about the same. Further investigation into the reasons for such performance is worth undertaking. This will require extensive analysis of heat-flow patterns and temperature profiles.

Another point of note is the temperature difference used 38K [+21C -18C] Not likely in the UK anytime soon.

Posted By: squowse plain 4mm float units should be no more than £40 sq/m (inc VAT).

I wish.

Thanks for the contact, but I've placed a deposit and they've begun manufacturing - told you time was short!
Hopefully it will help the next person in pursuit of better glazing.

Sorry -earthshipally I completely missed that squowse had whispered an email address to me, not posted for the forum.

As to your own question I'm sure some experts will be along to help, but you might want to expand a bit on where you are and what you need to achieve?

<blockquote><cite>Posted By: earthshipally</cite>All glazing south facing, Design of structure; heavy thermal mass, passive solar, (33% glass area)
soft or hard coat??? double or triple ??? Planning on external insulated shutters for use in winter

Been thinking this over for some time need help!!
thanks </blockquote>

So we're saying that for krypton a 14 spacer gives better edge performance (less edge loss), which overcomes the worse centre-pane performance (greater centre loss) due to wider-than-optimal cavity? And that for argon the similar widened spacer figures are 14 vs 12, i.e. less of a hit to centre-pane performance with argon, compared to what krypton suffers. So krypton may not deliver its promise fully, because compromised by over-wide cavity in order to minimise edge loss.

What's the width of the edge-band that's affected by the spacer's conductance? The edge band must have more dominant effect for small panes, justifying wider cavity to minimise edge loss - for larger ones the centre would dominate, so cavity would remain small, to optimise centre-pane loss.