We found a decent supplier/fabricator of Senior Architectural Systems.

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

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.

Posted By: VictorianecoRussell not interested

Ah, 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.

**What should I really aim to be specifying? Or aiming for?**

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).

Do you mean they insist on 3G, or it has to be 400 if you want 3G?

So 36 aka 4-12-4-12-4 i.e. 12 gaps not the optimum 16, unless using expensive fill gas other than Argon. Prob 4-16-4 2G would be just or almost as good.

There's millions of em - I'd ask Smart themselves to recommend one or two alternatives. Better check their hardware, handles etc, and how it feels to open/close - fundamentally a lo-cost system (but works fine). To get better than U1.4 (BldgRegs minimum) will require fancy glass specifications.

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.

Those 2G specs are non-optimum for Argon 2G. In other words, for same manufacturer's material costs, you cd get better performance, if optimised. Likewise, the 3G spec is non-optimum for Argon 3G.
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.

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.

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.