Posted By: VictorianecoI'm sure I recall someone suggesting it is better to have 2G on South facing windows and 3G on all other elevations.

Is there any fact in this or am I barking up the wrong tree?

3G can have better thermal insulation but/and also has less solar transmission (without solar control films etc). So it can make sense to have glazing that lets more sun in on the south elevation and better-insulated glazing elsewhere. But don't forget things like the number of seals on the frames etc. It's all a question of how much money you want to spend and the best ways to allocate it.

Am I also correct in thinking if the house will be EWI'd then internal opening windows would be the better option?

I don't think it makes much difference. It's quite common to insulate over the outside of the frame but you can do that with either type. Good quality windows can be had in either style.

I would go for internal opening windows with good quality multiple sealing. It makes it much easier to clean your windows. I think, but prepared to be corrected, that internal opening windows is mandatory in Scotland. I wish we had gone for such an arrangement.

Posted By: djhquite common to insulate over the outside of the frame

Either outside or inside or both (ideally) depending on your detailing.

The additional cost of a third sheet of glass is tiny and so go for quality frames with 3g.

Re: inward opening, we are loving ours, and the four levels of draught seals work brilliantly.

I am more concerned about energy use reduction, long term sustainability, and wellbeing

Posted By: fostertomso the new thinking is that cutting that part by one third is important, and trumps maximised Uvalue, in the trade-off that is the LCA calc of lifetime climate effect.

I don't always agree with this, on the basis that it doesn't factor in internal surface temperature and the perceived comfort (no downdraughts, noise etc.) that 3G brings.

Whilst I acknowledge that drowning in melted icecaps isn't comfortable either, it's easy to rush into the embodied carbon argument with the same zeal as the operational energy discourse and lose some of the nuance around behaviour and experience that can't be as easily quantified in hard numbers.

Counting embodied carbon on one of our larger projects we realised that the transport factors (e.g. diesel van vs electric) and even diet choices of our painters and decorators was probably going to rival the impact of a 1mm layer of paint if you start to factor in all of the variables.

So I guess I'm saying that some perspective is always needed. Usually better to make slightly smaller windows in the first place and take the saving on all the panes.

Posted By: revorI wish we had gone for such an arrangemen

I wish I'd gone for outward opening on the front elevation that gets absolutely battered by wind and rain; the rain keeps em clean and the harder the wind blows the more it would seal the windows of

Posted By: djh

Posted By: cjardthe harder the wind blows the more it would seal the windows

If you're relying on the wind to seal the window, there's something wrong with the window design. The seal should be held by the mechanical latches regardless of what the wind does.

It is not a symmetric situation though. Pressure variations on the outside are much larger than those on the inside and my guess is that positive pressures are higher than negative ones, as long as we are not talking rooflights.

Agreed that inward opening makes cleaning a whole lots easier; I know because mine are all outward opening.
However, outward opening are more weather proof than inward. When I built, I was told that outward tend to be waterproof while inward tend to be only weatherproof.

But what do I know?

>>>> "2G on South facing windows and 3G on other elevations"

Think this was from the Passivhaus Trust, it was a few years ago, so possibly the balance between heating and manufacturing has shifted further towards 2G now.

https://www.passivhaustrust.org.uk/guidance_detail.php?gId=54

They also mentioned that wood frames are lower carbon than alu. Quality is important so the windows last long and do not need replacing, with another set of manufacturing emissions for the replacements.

>>>>"water proof"

Our windows in Scotland are often inward opening because Scottish building standards require windows that are safe to clean. We certainly do get storm driven sideways-rain more often than not, and the windows don't leak.

We need to see some EPDs for 2G vs 3G windows. If the 3rd pane only adds slightly to the overall as-installed embodied carbon, but reduces in-use (50yrs? 100yrs?) eventual accumulated emissions by at least twice as much (it's the area under the accumulating curve that matters) and also significantly reduces occupants' subjective perception of 'cold' radiation as 'draughts' therefore their tinkering with hopefully optimised controls (which the 3rd pane apparently does), then we keep on using 3G.

I've started asking suppliers for their EPDs. Quite impressed with good ol'fashioned UK-meagre-U-value aluminium window extruders Smart, who seem to be making great efforts to reduce manufacturing emissions and point to the excellent recycling of, therefore modest process emissions of, aluminum generally, second only to timber for windows, and have EPDs under development. I looked at Smart because they've introduced an aluminium 'Heritage' replica of Crittall-style windows using even skinnier alu sections than their mainstream, and vastly improving on the negligible U-value, airtightness etc of Crittalls, to typical U1.1 i.e. same as my favourite 4-12-4-12-4 (sub PH, unbeatable cost) Russell timber windows.

Many areas of northern Europe have colder winters than we do. Continental climate versus maritime climate.

In PH the requirement for window performance has a lot to do with maintaining a temperature of 17 °C on the inner surface of the window, which in turn is important to eliminate convection down the window. AIUI anyway.

I remember that adjusting (reducing) the size of windows on the north facade was one way our design was made to perfom in PHPP.

Posted By: tonystraightforward money spent vs cost /energy savings

Yes, because we used to think energy was a proxy for greenhouse gasses, but nowadays it's far from equivalent. Some energy these days is GHG-harmless; other kinds of energy far more harmful to climate emergency than we imagined. So now we must think of harm to climate emergency rather than energy consumption. Unless we only care about money spent on energy, not so much about its effect on climate emergency?

What's the price from SMART Tom? Compared to timber?

Do you have a link or contact source please?

Okay I've seen there's a local supplier but Russell sounds appealing.

On a seafront, how bad are timber windows?