Design Solution · Building Envelope
Design Solution · Dream about it
Model and reduce curtain-wall joint psi-values and glazing U-values to cut heat loss.
Each curtain-wall thermal joint (mullion, transom, head and cill) is modelled and the psi-value driven down through detail variations and improved glazing. Moving from as-built double glazing to higher-performance and vacuum glazing dropped the unit U-value from around 2.15 to 1.26 W/m2K, lowering heat loss and improving compliance margins.
Every curtain-wall joint — mullion, transom, head, cill — is a thermal bridge, and their cumulative effect on a glazed commercial building can undermine the fabric performance implied by the glazing unit U-value alone. This solution models each joint in detail, drives down psi-values through detail variations, and pairs that with higher-performance glazing to close the gap between certified component performance and whole-element heat loss. The illustrative data here — U-value improvement from roughly 2.15 to 1.26 W/m²K — is specific and credible as a design target, though the record carries only claimed status and the as-built performance of the referenced project has not been independently verified. The value is most material on buildings with a high glazed-to-opaque ratio in heating-dominated climates, where thermal bridges can account for a disproportionate share of fabric heat loss and can tip compliance calculations. The discipline required is upstream: psi-value optimisation depends on having fully developed connection details and agreed glazing specifications early enough in the design programme to feed into energy modelling iterations rather than appearing as a late substitution. The honest risk is that contractor substitutions during procurement — different framing systems, lower-specification glazing units — can erode calculated improvements substantially, so specification enforcement and post-installation verification are as important as the design-stage modelling.
#thermal bridging #curtain wall #glazing #U-value