Green Building Forum - Final Window Conundrum Thu, 25 Jun 2026 05:19:52 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309522#Comment_309522 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309522#Comment_309522 Mon, 20 Oct 2025 19:39:15 +0100 Victorianeco
2 products with differing specs:

Ali Vu
https://www.seniorarchitectural.co.uk/architectural-systems/ali-vu-window/
Standard Casement Opening Outward (not available in T&T)
Total Project Cost (S&F) = £21,030

PURe
https://www.seniorarchitectural.co.uk/architectural-systems/pure-window/
Tilt & Turn
Total Project Cost (S&F) = £30,115

Both are based on 28mm Triple Glazing (4-8-4-8-4), Low 'e', Black Warm Edge Spacer
Inclusive of aluminium cills - not required as EWI?

My query is T&T worth an additional ~£10k?

I am trying to work out what the U-Values are as the spiel states the former as low as 1.0 and the latter 0.71 but I don't know what configuration of glass these are based on as both frames can accommodate up to 44mm

So my questions are thus;

1. What is optimum make up of glass so I can get a more accurate spec. The fabricator said the glass cost wont make much difference to the price
2. Anything else to ask at this point?

Thanks]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309523#Comment_309523 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309523#Comment_309523 Mon, 20 Oct 2025 20:22:12 +0100 fostertom Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309524#Comment_309524 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309524#Comment_309524 Mon, 20 Oct 2025 20:42:58 +0100 djh Posted By: VictorianecoBoth are based on 28mm Triple Glazing (4-8-4-8-4), Low 'e', Black Warm Edge Spacer
Inclusive of aluminium cills - not required as EWI?You still require sills with EWI, unless you know something I don't?

4-8-4-8-4 seems quite narrow gaps? The optimum glass spacing depends on the gas fill. IIRC it's 16 mm for argon and 12 mm for [more expensive] krypton fill.

Posted By: VictorianecoMy query is T&T worth an additional ~£10k?
The two types of windows have different U-values, so you're not comparing like-for-like. IOW your question isn't sensible.

In terms of glazing, you need to consider toughened vs laminated and soft coatings etc. Pilkingtons or Saint-Gobain have loads of information.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309525#Comment_309525 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309525#Comment_309525 Mon, 20 Oct 2025 21:12:13 +0100 Victorianeco
The quote form link above:

"High performance polyamide thermal barrier giving U-Values as low as 1.0 W/m2K when calculated as a domestic CEN Standard window"

Elsewhere I found:

"Very important is how window sizes affect U-Values. Simulations to establish U-Values are typically calculated using a standard window size of 1.23 m x 1.48 m. This is called the CEN standard developed by the European Committee for Standardisation (CEN)."
https://www.doorandwindowexperts.co.uk/47854/the-ultimate-guide-to-window-u-values/]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309526#Comment_309526 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309526#Comment_309526 Mon, 20 Oct 2025 22:25:34 +0100 fostertom Posted By: VictorianecoRussell not interestedAh, I remember you said that - they need the buyer to v fully specify all their options (which aren't concisely described, so I don't know how I or anyone came to learn them!).
Posted By: Victorianecogiving U-Values as low as 1.0 W/m2K
Sounds like they're talking about glass-only U - albeit the whole unit not just centre-pane.
Last para is correct. Larger windows should give better U-value, having proportionately more of the centre-pane.

if 3g is only 4-8-4-8-4 gaps, prob 2g 4-16-4 wd be as good or better, and less embodied carbon.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309527#Comment_309527 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309527#Comment_309527 Tue, 21 Oct 2025 14:05:29 +0100 Victorianeco
What should I really aim to be specifying? Or aiming for?

Thanks]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309528#Comment_309528 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309528#Comment_309528 Tue, 21 Oct 2025 15:16:35 +0100 Nick Parsons
Minimum 4/16/4/16/4, 2 soft-coat Low E coatings, argon and warm-edge spacers. Mine from Green Bldg Store (now 21 Degrees) are 14/18/4/18/4/2 x soft-coat, low E glass, W/E spacers and argon. 0.8 whole unit U value (incl frame).]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309535#Comment_309535 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309535#Comment_309535 Thu, 23 Oct 2025 19:14:52 +0100 Victorianeco
What about this supplier:
https://cwgchoices.com/choices-range/windows/alu-clad/tilt-and-turn/

Appears to be the same windows as ALLAN Brothers - or the pictures look the same at least from their website.

Thanks]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309536#Comment_309536 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309536#Comment_309536 Thu, 23 Oct 2025 23:05:17 +0100 fostertom Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309537#Comment_309537 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309537#Comment_309537 Thu, 23 Oct 2025 23:57:07 +0100 Victorianeco Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309538#Comment_309538 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309538#Comment_309538 Fri, 24 Oct 2025 08:56:09 +0100 fostertom Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309539#Comment_309539 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309539#Comment_309539 Fri, 24 Oct 2025 10:00:22 +0100 Victorianeco
I've seen them in person in a showroom and I think this system suits the property not being too thick frames like aluclad and I really don't think spending an extra £10k for slightly better U values adds merit in terms of cost v benefit]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309540#Comment_309540 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309540#Comment_309540 Fri, 24 Oct 2025 10:19:05 +0100 fostertom
I like the adaptation of the standard range (well-chosen selection of components and some extra sections) that allows them to call it their Heritage range - a fair imitation of traditional (1920s-1950s) Crittall galvanised steel windows, but with some insulation (1.4) vs basically none. But to actually get the slim-sightline look, some careful choices about the numerous alternative sections (e.g. bevelled vs square glazing beads, and more) need to be made - or checking and re-checking the fabricator 'gets' the kind of look you want.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309541#Comment_309541 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309541#Comment_309541 Fri, 24 Oct 2025 22:51:47 +0100 Victorianeco
4-20-4 Argon fill
4-12-4-12-4 Argon fill
3/3-18-4 Argon fill

Not got prices for each option but I'm really thinking of going down the self order route. Can't be that difficult to install frames into a non existent outer skin? Plenty of YouTube videos about]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309546#Comment_309546 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309546#Comment_309546 Sun, 26 Oct 2025 08:01:28 +0000 fostertom Tho as we know the price they quote may have little to do with material costs, more to do with volume at that spec, and premium-pricing for e.g. 'Passive House grade'.
20 or 18 is too wide for cheap-default Argon - 16 is optimum.
That 3G spec will be a little bit better than any Argon 2G, tho 12 is below optimum for Argon; it could perform quite a lot better with a more expensive gas fill, which is not only better-insulating but for which 12 is optimum. With Argon fill, 16 gap is optimum.
3/3 sounds like laminated glass - why would you? Some of your windows may need 'safety glass' (BldgRegs gives the rules) but usually 4mm toughened is used rather than 6mm laminated.
Any 3G, any exotic gas fill, and any aluminium frame, is going to have significantly higher embodied carbon than 2G, Argon filled, in a timber frame. Embodied carbon (i.e. carbon emissions created in mining, manufacturing, transporting and constructing) is now recognised as just as important, if not more so, than in-use creation of carbon emissions.

By self-order, do you mean you install yourself, or your builder does it, rather than seeking a supply-and-install quote? I'd be surprised if any supply-and-install co has any idea how to install outboard, ready for EWI; they might slap on a massive extra charge when they get to site and realise what you intend, and you'll have to know exactly how you want it done.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309547#Comment_309547 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309547#Comment_309547 Sun, 26 Oct 2025 13:08:43 +0000 Victorianeco
Maybe I should revisit Russel and see if they are interested now we are ready to proceed on at least 5 windows and a pair of sliding doors.

Do you happen to have the dimensions of their alu-clad range? I'm particularly interested in knowing the power frame widths and what the vertical weights would be between a fixed unit and an opener.

My windows are very basic as 5 are all the same size, 3 with the opening sash on left hand side and 2 with sash on right hand side.

I'd even be tempted to get supply only and get the glass locally, we have very good terms with a local glass firm.

Do they do unglazed? Anything else I should be thinking of to ask Monday?]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309549#Comment_309549 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309549#Comment_309549 Sun, 26 Oct 2025 17:37:12 +0000 djh Posted By: VictorianecoChat got suggests 20mm argon fill is about optimum fit 2G, unless you go for vacuum or Krypton then you can go narrower.Presuming you mean chatgpt then I think it's basing its "opinion" on American standards that are not relevant in the UK. So here, 16 mm is optimum, 20 mm is not too bad and 12 mm is to be avoided!

My windows are very basic as 5 are all the same size, 3 with the opening sash on left hand side and 2 with sash on right hand side.
Be sure to double or triple check whether the "left" and "right" are stated with a view from outside or inside.

I'd even be tempted to get tinder only and get the glass locally, we have very good terms with a local glass firm.
"tinder"? Good units are supplied glazed.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309550#Comment_309550 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309550#Comment_309550 Sun, 26 Oct 2025 18:28:19 +0000 Victorianeco
So a 4-16-4 would be better than a 4-20-4? Seems counter, intuitive.

Was meant to say supply only....]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309552#Comment_309552 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309552#Comment_309552 Sun, 26 Oct 2025 20:25:28 +0000 djh Posted By: VictorianecoSo a 4-16-4 would be better than a 4-20-4? Seems counter, intuitive.As the gap gets wider, convection currents become more possible making the performance worse. At the lower temperature used in American standards, convection is less likely, I believe.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309554#Comment_309554 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309554#Comment_309554 Mon, 27 Oct 2025 08:30:01 +0000 Victorianeco
Argon fill, Low E coating

I would like a bit extra sound deadening if possible as we live in an exposed area and the wind can become loud particularly in the Winter months!

I'll make some calls today and see what I can get sorted

Thanks all]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309557#Comment_309557 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309557#Comment_309557 Mon, 27 Oct 2025 12:47:40 +0000 djh Posted By: VictorianecoI would like a bit extra sound deadening if possible as we live in an exposed area and the wind can become loud particularly in the Winter months!Triple glazing, without trickle vents and with good air-sealing (i.e. PH) is quite quiet. I once visited Utrecht radio station, which is at a busy roundabout, and they had 10-glazing to reduce noise! Recording studios don't have windows, in general.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309559#Comment_309559 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309559#Comment_309559 Mon, 27 Oct 2025 13:14:19 +0000 owlman Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309560#Comment_309560 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309560#Comment_309560 Mon, 27 Oct 2025 16:29:09 +0000 Victorianeco Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309561#Comment_309561 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309561#Comment_309561 Mon, 27 Oct 2025 17:25:18 +0000 fostertom Posted By: djhTriple glazing, without trickle vents and with good air-sealing (i.e. PH) is quite quietSo that's only partly about the glass, more I'd say about the frame's air-sealing, and I'd add, any extrusion cavities and/or holes that are open to outside, which can (usually do) have a wind-speed/direction at which they resonate like an organ pipe or whistle. Hard to be sure about all that in advance, but timber windows aren't at such risk, unless they have external aluminium facings.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309562#Comment_309562 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309562#Comment_309562 Mon, 27 Oct 2025 20:32:00 +0000 Victorianeco Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309564#Comment_309564 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309564#Comment_309564 Mon, 27 Oct 2025 21:22:57 +0000 fostertom Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309565#Comment_309565 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309565#Comment_309565 Tue, 28 Oct 2025 07:53:25 +0000 Victorianeco
So I guess that isn't optimal either then]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309566#Comment_309566 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309566#Comment_309566 Tue, 28 Oct 2025 09:02:37 +0000 fostertom
I use Russell for 'modern' applications, and accept the premium for Vrogum when it's an older window-style to be matched, as Vrogum are unique in the trade in making their opening sashes glaze-in, while everyone else does glaze-out - as Vrogum do also for their fixed lights. Vrogum's glaze-in sashes present a slim 45o bevel to the outside, which looks pretty much like the putty-line of a traditional cottage window or a posher Georgian/Victorian/till-1920s classic hinged or sliding sash window. To achieve that look, all openings have to have a sash inserted, whether hinged or fixed, as their direct-glazed lights don't look like that. There are other options/features that must also be specified, to make the 'look' work.

Anyway, none of that is relevant to Victorianeco's project, which is 'modern'. Just to say 'yes' to Vrogum.

Also to say that despite previous alerts about 16 being optimum gap, I generally do settle for 12 gap 3G, both with Russell's super-value range (they charge premium for basically the same window but 'PH grade' with 16 gap and double seals) and with Vrogum (with all-opening lights - I have no need of their fixed lights with 8 gap). Even with 12 gap 3G, at U1.1 they beat any aluminium window at U1.4 unless you spend more on exotic fill gas. Alternative to 12 gap 3G, 16 gap 2G is prob almost as good, so I'll be doing that in future, for minimised embodied carbon.]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309567#Comment_309567 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309567#Comment_309567 Tue, 28 Oct 2025 11:18:34 +0000 djh Posted By: VictorianecoIndigo 7 quoted me for the Vrogum timber windows in a 5-8-4-8-5 for the fixed sash and a 4-12-4-12-4 for the openerAIUI, Vrogum's standard glazing has 16 mm gaps,so why the very narrow gaps? Did you ask for something very slim overall or something?]]> Final Window Conundrum https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309568#Comment_309568 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18366&Focus=309568#Comment_309568 Tue, 28 Oct 2025 11:54:15 +0000 Victorianeco