I am currently looking at wooden and aluclad windows and have contacted a number of the companies recommended on this post. All of these companies have been great so far.
As a matter of interest, is it possible to have a u-value of 0.6 in the glass and a combined u-value (glass and frame) of 0.8?
passive houses recommend u values for windows between 0.63 and 1.3... so it must be possible.... again it all depends on the spec of the window.
Ecoglaze claim to be able to get a u value of 0.68 with their 'edition' window... triple glazed alu-clad timber windows with krypton gas fill. These are austrian Internorm windows...