"PVC has to be used due to weight and size being a factor I believe."

I believe you are incorrect in your thinking but without more info impossible to tell. Is this in the US? It is only approx. 14'-8" x 5'-6". Definitely should be other options than UPVC. Not saying UPVC may not be your best option just that there certainly are other options.

It could be that uPVC is considered as it has higher efficiency? I will ask the window company today. I have asked for max efficiency and quality. I thought it was because of the weight but possibly not.

I need to know if there is a big difference in the efficiency and u-valve measurement

"It could be that uPVC is considered as it has higher efficiency?"

Could be but you have not given us enough info to offer much in the way of help. "U" Value will definitely have much to do with the energy efficiency of the windows.

millworkman I think you meant 8' 6"...

I can only imagine that you are looking at multiple smaller windows that will be either mulled (joined together) or else individually mounted in a framed wall?

uPVC may be the choice for efficiency from this manufacturer. There will be other efficient choices from different manufacturers with different color options. I'd investigate some more.

My quote and specs are in Italian so ive used goodle translate. Im still not fluent! And i am trying to get pictures.

"Good morning, as per your kind request, I am sending you the estimate of the Internorm model KF410 windows, they have the following generic characteristics: - 93mm frame with six chambers; - standard triple glass according to law with safety tempered glass (to avoid possible shocks thermal insulation) with perimeter glazing I-Tech glazing to ensure stability, thermal insulation and a exceptional safety; - black ISO glass spacer channel; - triple perimeter seal; - hidden hinges and satin chrome handles; - tilt and turn standard on windows and French windows; - color: internal wood effect film or pvc / external aluminum shell wood effect painted. POS.160: Lift and slide model KS430 - 200mm frame with six chambers; - triple glass with safety tempered glass (to avoid possible thermal shock) with gluing perimeter I-Tech glazing to guarantee stability, thermal insulation and exceptional safety; - black ISO glass spacer channel; - internal square G80 satin chrome handle and Dallas satin chrome external handle; - color: internal wood effect film or pvc / external aluminum shell wood effect painted"

Example of a frame: 1 fixed door and 1 sliding:

Frame width: 4500mm, Frame height: 2600mm,

Div. In width: 2250/2250, Disassembled version,

Frame: Normal frame, Lowered threshold,

Fields: FIX / IF,

Fixed element:

IF door:

Lifting door (HST) Left side: right,

Item version:

Transport depth / coupling: Without transport profile (-)

Extras: Internal glass seal color: Black, Glass seal color

ext .: Black,

Pre-drilling for 3-sided screws (81)

Altitude (a.s.l.) <700 m

Transport: Logistic XL transport costs, The outer plate comes

made of ESG-H instead of ESG., Edges of float glass sheets

if> 1700 x 2500 mm,

Uw (calculated on described finish, EN ISO 10077): 0.78 W / m²K

Where is the home being built?

Italy I think and IMO often in Europe for large windows clients go commercial metal windows both for esthetics and function. Yes you could easily do charcoal and white this is done all the time in the US so pretty sure easy to do in Europe.

@millworkman the house is being built in Italy. I am adding a huge modern glass extension looking over the Apennine mountains

So this evening i went to see the glass company and finally i have a choice of the inside and outside being the same colour. Then of course i had wrecked my head for a week thinking i couldnt and now i find it hard to decide to have outside and inside charcoal grey OR outside charcoal grey and inside white.

The material is recommended is uPVC with aluminum surround on the outside due to weather conditions