Just chancing that there may be window expert willing to give some tips.

I noticed on some professional renovation projects that they have used glass dividing glazing bars. i.e. Windows are made up of several small panes joined with a sub-frame.

I've also now discovered while pricing that this style actually comes in cheaper for e.g. large window divided into 12 sections, in comparison to using 2 larger pieces of glass with the glazing bars glued on externally. Surprise to me.

I can think of another 2 advantages, in terms of ease of ease of installation there are only small pieces of glass to handle and a single piece of damaged glass would be considerably cheaper to replace in the future and there would be no problem of matching the finish of the glazing bars as they would not be changed.

Presumed disadvantage and why I never considered this option before was that the sub-frame would considerably impact the overall u-value of the window, in comparison to using a large piece of glass. Does anyone know if this is true?

And other realted tips?

edit : just adding a link to a picture of the ones I was looking at

https://3.bp.blogspot.com/-FRzj_VT3tcI/WzIETqZhV_I/AAAAAAAAD7E/0xxAyzXknugsJGOHR4eQAbQE7Q6t1paCACLcBGAs/s1600/Marktzentrum%2B%2B06.JPG

Generally the thermal weak point of windows is the fame. The timber elements will be approx twice as bad as the glass components, or more, depending upon the wood and the glass. I find it difficult to see how many smaller glass units will be cheaper than one large unit as usually 2g or 3g units are priced by the glass/m2 plus the edging by m run and there will be considerably more edging with smaller units. Whilst sticking on fake Georgian effect will add to the cost of the glass unit the cost of making Georgian casements will be considerable compared with windows with single or double lights.

In addition to the comments by djh above small glazing units as in Georgian windows or the ones shown in the OP are a pain to clean compare with large windows.

The reasons for the divided windows as shown in the renovation IMO will be the aesthetic look rather than price, although large windows as shown if they are a single units will have specific safety requirements not applicable to small units, which will add to the cost but I would not expect that cost to out weight the cost of the purpose made timber frames shown in the photo.