In the event you don’t want thick double glazing, trim double glazing has width of only all over 14mm (Though some are as slim as 10mm) and is more efficient. The U-Value (the measurement that signifies the window’s thermal efficiency) is better and slender glazing is much more aesthetically pleasing. https://sashwindowdraughtproofing50504.wizzardsblog.com/35778587/not-known-facts-about-sash-windows