I e-mailed Fakro and they sent me a bit more information about their FTT (triple glazed roof window) as mentioned by krishna. Apparently they use 'warm' TGI spacing frames and krypton fill. The sash frame is approximately 30% thicker than a standard Fakro or Velux window. I think, although cannot find confirmation, that the Fakro windows typically have an external finish of polyester coated aluminium, not so green but probably makes them last longer.

Interestingly, their pricing for standard centre pivot windows matches Velux exactly! Prices for the triple glazed alternative are typically 30% more expensive, with some sizes around 15% more and others almost 50% higher. You pays your money...

For anyone reading this forum from the USA I would recommend www.alpeninc.com. (They won a top 10 green building award in USA)

For anyone reading from elsewhere, try looking for windows with "Heat Mirror" films. Adding a 3rd layer of glass makes the window heavier which is not typically an issue unless you want impact resistance or lamination for sound deadening. The Heat Mirror films are very light weight and come in various formulations and single and double coated. Alpen make windows with up to 3 films (4 gas spaces) and up to double coated. The more films and coatings the more the tinting effect, so it is important to see an example. I'm ordering mostly with two single sided films (some with two double sided films). The center of glass R value is about 9.5 (US units) for two single sided films.

The price comparisons are already publised, in this thread.

Various kinds of 'patent glazing' available - 3g glass units installed direct into metal and/or timber rafter/carrier system on site.

PS If the roof pitch is shallow/flat you cant use regular beading/putty to hold units in or you will get standing water. Needs a bit of careful design.

Patent glazing works at very low pitch because it assumes that water may get in past the edges of the glass/3g units, and has a drainage channel to catch it and drain it safely away. Patent glazing can be all-aluminium incl. basically a I-section rafter, or it can be just an aluminium carrier that rests on top of some other kind of internal structural rafter, e.g. timber.

Hi,

Going back to the BRFC rating method. having looked at their info does anyone have any typical values for the m3/m2/hr figure for the infiltration. I'd like to try some approx calculations but dont have any idea what sort of values to expect or what would be given for the infiltration value by manufactures for different window types. From their info sheet this is x 0.0165 to get a w/m2K value to add to the U-value (happy with those). This is subtracted from the solar gain bit. I'd be inclined to ignore the gain and judge on simple losses, but right now i'm just trying to get afeel for their ratings.

Cheers, Mike up North

thanks tom
I've copied it below
I presume these prices are unfinished soft wood preglazed ?

"Triple glazed soft-coat Scandinavian-style timber windows being quoted at £300-330/m2 delivered, presumably less for a whole office block. The cost of triple over double is so small as to make it a no-brainer - but the choice of UK suppliers whose rebates are deep enough for 4-12-4-12-4 units is few:

Russell Doortech, manuf'd in Glasgow or by Norwegian associate, 0141 958 0444 (whose quote I have recently accepted)
Tanums (import) 0115 9321013
SP (import) 01347 825610
The above three are in that price range; the following are more:
Sashless, manuf'd in Yorks to a design developed at my request 01609 780202
Green Building Store, manuf'd in Yorks, the eco bees knees but very expensive 01484 653765

The absence of several household names, who can still only do double glazing, is striking , incl. Rationel (import), Eco Merchant (Vrogum import), Scandinavian Window Systems (various import), and giant empire Inwido who have swallowed the once-excellent Swedhouse. That the majority of suppliers included are UK manufacturers in also surprising - Howarth, of Air-Supply Window fame, have a design under development too. A few other companies blew the invitation to quote in one way or another, so there may be others.

Other companies e.g. Vrogum and Inwido do even higher-spec 3G windows with 4-16-4-16-4 glass and frames timber/cork laminated frames, for European-market Passivhaus etc use. And there's Canadian sources, esp. interesting glass-fibre framed - Paul in Montreal has the info.

There are other ways of doing triple glazing e.g. Velfac's aluminium outer/timber inner stuff, which can also be made up into slim-sightline facade frame assemblies.

Spoke to Rationel and EcoMerchant yesterday, both of which will be supplying me with 3g info / prices so seems they do supply them...

J

I also noticed the lack of info on 3g on the Rationel website, but the chap I spoke to on the phone swears they do it, as for EM I have the Viking 3g info in front of me right now,

J

Just joined the forum and fascinated by the 2g/3g discussions - excellent debate. Let me tell you a story. A late friend of mine when registering for war service in 1939 had to answer the question "Nearest Capital City" and the options were Edinburgh and London. He scored out both and answered Oslo.
Let me remind folk that in the north of the UK we are almost Scandinavian, geographically and in climate. The vast majority of Scandinavian glazing is 3g and well engineered - and for years folk in this part of the world naturally glance east to our nearest neighbours and note with interest their ideas and concepts. Some are considered and some discarded. Look at the 97% Heat Pump usage in Scandinavia - now there is another debate!!

Haggis,

Look at old yorkshire dialect words and town names, and then look for the origin, and guess what? Norwegian is the source!
Probably have the same in Scotland.

>>In conclusion the report suggests and endorses that aluminium clad timber windows will provide an expected service life in excess of 40 years.

>>Timber could not hope to achieve this, even with a regular maintenance regime.


Oh Bugger! My windows must be figments of my imagination.

I wondered when Velfac would make a corporate appearance.

At last we have an answer, they do triple glazing.

Centre pane or overall U value Mr Velfac?

Must be quality lead paint on those windows Tony & Mark!

Surely the idea that victorian windows show that timber windows should last forever is a little bit misleading?

Firstly, your sample is skewed. You don't see rotten Victorian frames.. because they rotted and were replaced. Just because your windows have lasted a long time doesn't mean all Victorian windows lasted a long time.

Secondly, building styles were designed to protect the window - deep insets kept the frames out of the weather, whereas today windows are placed a short distance from the wall surface and are much more exposed. I'm not sure there were that many Victorian timber framed rooflights?

Thirdly, wasn't the sort of timber used very different to modern supplies? Hardwoods, much slower growing softwoods and significantly slower seasoning all made for much more durable materials, which in today's industry would cost significantly more. Whether they were as sustainable, or as scalable to mass production is open to question.

Finally, I suspect the Victorian attitude of 'make do and mend', combined with a much larger manual workforce made maintenance a completely different game from todays 'fit and forget' ethos.

So I don't see the problem with a company trying different techniques to extend the lifespan of modern, mass produced and affordable timber frames?