Glazing Basics: Reading the Numbers Without the Noise

U-value: heat moving through

U-value describes the rate of heat transfer through an assembly under defined conditions. Lower values generally indicate less heat transfer, but compare like with like: centre-of-glass figures are not the same as whole-window figures, which include frame and edge effects.

Request the scope and test basis behind any figure. A number without its unit, configuration and reference standard is incomplete information.

Solar heat gain: energy arriving with sunlight

Solar heat gain coefficient, often abbreviated SHGC, indicates the fraction of incident solar energy transmitted through the glazing system. A lower figure usually means less solar gain. The appropriate balance depends on orientation, shading and desired daylight.

Do not treat the lowest available value as automatically suitable. Dark or highly reflective glazing can change interior brightness, exterior appearance and night reflections. A representative sample viewed in real conditions is more informative than a small swatch under showroom lighting.

Visible transmittance and glare

Visible transmittance describes how much visible light passes through. It is useful alongside SHGC because two products can manage solar gain while producing different daylight conditions. Room depth, wall colour and neighbouring buildings also affect perceived brightness.

• Review the glass from inside and outside.
• Check colour under sun and shade.
• Consider screen and curtain layers.
• Assess glare at the actual viewing angle.

Safety, laminated and tempered glass

Safety glazing requirements depend on location and applicable rules—for example near doors, low-level openings or areas with human impact risk. Tempered and laminated glass behave differently when broken. Laminated glass uses an interlayer that can retain fragments; tempered glass breaks into comparatively small pieces.

Only a competent project professional can determine the required glass type and thickness for a specific opening, loading condition and location. Keep glass markings and documentation with the property records.