Nothing in the headline requirements changed this year. What changed is the evidence. Codes in several markets now require the assembly performance of the installed unit rather than the centre-of-glass value of its component.
Why it matters commercially
It moves the specification conversation from the glass manufacturer to the fabricator, which is where the honest number has always lived. Manufacturers are adapting, but slowly.
Thermal bridging
The spacer and the frame edge are where the losses are, and they are the hardest elements to model. A number of test methods now exist, which is progress.
What to do now
Ask for a whole-window U-value with the calculation basis stated. If the supplier cannot state the basis, the number is not comparable.
