G-value (solar factor / SHGC)

The g-value — also called the solar factor or solar heat gain coefficient (SHGC) — is the fraction of the sun's radiant heat that passes through a glazed unit, on a scale of 0 to 1. A g-value of 0.4 means 40% of the solar energy hitting the glass ends up as heat inside. In Dubai you want it LOW, because blocking radiant solar heat is half the battle against the cooling load — the other half being conducted heat, which is the U-value. The two are different and you want both low: U-value handles the temperature-driven heat, g-value handles the sunshine-driven heat. Low-E coatings, body tints and reflective coatings all pull the g-value down. The catch is the trade-off with visible light: push the g-value very low with heavy tint and you also darken the room, so good glazing aims for a low g-value while keeping reasonable daylight (a high 'light-to-solar-gain ratio'). When you're specifying facade or window glass for a sun-exposed elevation, the g-value is the number that most affects comfort and running cost — one to get right with Al Ghubaiba's glazing and façade team rather than choosing on frame looks alone.