Design Solution · Building Envelope
Design Solution · Dream about it
Use vacuum/high-performance glazing for very low U-values in slim build-ups.
Vacuum-insulated glazing units achieve very low centre-pane U-values (around 0.7 W/m2K) in a slim build-up, well below conventional double glazing. Used in curtain walls they cut fabric heat loss while keeping sightlines slim and suit retrofit where frame depth is fixed.
Vacuum-insulated glazing achieves a centre-pane U-value around 0.7 W/m²K in a unit typically 6–8mm thick — comparable to triple glazing in thermal performance but at a fraction of the depth, which matters directly on heritage retrofits and slim curtain wall systems where frame depth is architecturally constrained. The physics is established, and units are in commercial production from manufacturers including AGC (Fineo) and NSG/Pilkington (Spacia); this is no longer a laboratory product. The gap between product availability and widespread specification is real: vacuum glazing is significantly more expensive per square metre than conventional high-performance double or triple glazing, edge seal durability over a 25-30 year design life is less established than the mature secondary glazing market, and point pillar spacers produce visible patterns under raking light that some heritage consents find objectionable. Thermal bridging at the edge and frame is also proportionally more significant when the centre-pane performance is this good, meaning whole-unit U-values are noticeably higher than the headline centre-pane figure. Worth serious consideration wherever slim build-up is a genuine constraint — listed building infills, slim-profile retained curtain walls, secondary glazing over single-glazed originals — but the specifier should obtain manufacturer durability data and price the whole-unit U-value, not the centre-pane figure.
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