Why Windows Feel Draughty
The sensation of a draught near a window can be caused by actual air infiltration (gaps in the frame or hardware) or by cold radiation from the glass surface. Cold radiation creates a convection current — cold air falls off the glass surface and flows across the floor, creating the feeling of a draught even when there's no actual air gap.
This distinction matters because the solutions are different. Air infiltration needs frame work (gaskets, seals, hardware adjustment). Cold radiation needs better glass — and that's where we come in.
The Impact of Glass Specification
The difference between old and new glass technology is dramatic:
Old clear glass, air fill: U-value ~2.8 W/m²K. Inner pane surface temperature approximately 11°C when it's 0°C outside and 20°C inside. Cold enough to cause visible condensation and significant cold radiation.
Low-E + argon: U-value ~1.1 W/m²K. Inner pane surface approximately 17°C in the same conditions. Warm enough to prevent condensation and virtually eliminate cold radiation.
Triple glazing: U-value ~0.6 W/m²K. Inner pane surface approximately 19°C — almost room temperature. Zero perceptible cold radiation.
The Warm-Edge Factor
Even with excellent centre-pane performance, a standard aluminium spacer bar creates a cold bridge at the edge. This shows up as condensation at the glass perimeter and a cold strip around the edge of the window. Warm-edge spacer bars (composite or stainless steel) reduce this edge heat loss by up to 65%, making the entire glass area feel warm and consistent.
Frame Considerations
Always assess the frame alongside the glass. A new high-performance sealed unit in a frame with perished gaskets or worn compression seals won't deliver its full potential. Recommend gasket replacement as part of the job when gaskets are visibly deteriorated. We stock standard gasket profiles, or can source bespoke sections for older frame systems.