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When you think about new windows, it is easy to focus on the frame and forget that the glass does much of the hard work. Glazing is what keeps heat in, noise out and your home comfortable, and the option you choose affects performance, sightlines and even whether a window suits a period or listed property.
Here is a clear guide to the glazing options we offer on our timber windows and doors, and how to choose between them.
The performance of glazing is measured by its U-value, in watts per square metre kelvin (W/m²K). It tells you how easily heat passes through, so the lower the number, the better the insulation and the less heat your home loses. A modern window should sit well below the old single-glazed standard, and the glazing you choose is the biggest single influence on that figure. Whole-window U-values also depend on the frame, size and configuration, so treat the figures below as a guide.
Double glazing is the established standard: two panes of glass separated by a sealed cavity, usually filled with an insulating gas. It offers excellent insulation and noise reduction for the majority of homes, and on our Lignum timber range it achieves a U-value of around 1.2 W/m²K. For most projects it strikes the right balance of performance and practicality, and it remains our most popular choice.
Triple glazing adds a third pane and a second cavity, pushing thermal performance further still. On our timber range it reaches around 0.9 W/m²K, making it a strong choice if you want the warmest, quietest result, live in an exposed location, or are building to high energy-efficiency standards. The trade-off is a thicker, heavier unit, so it suits some designs better than others.
Vacuum glazing is the most advanced option we offer, and it solves a problem the others cannot. Like double glazing it uses two panes, but instead of a gas-filled cavity, the air is extracted to create a vacuum. Because a vacuum transfers almost no heat, the gap between the panes can be as little as 0.3mm, far slimmer than any conventional unit. The result is exceptional thermal performance, with our vacuum-glazed timber windows achieving around 0.7 W/m²K, alongside excellent noise reduction and a long service life. Its slim profile is what makes it special: it can deliver modern efficiency while looking almost like original single glazing, which is why it has become the standout choice for heritage and listed properties.
For period and conservation properties where the look of the original windows must be preserved, slim heritage glazing offers narrow sightlines that conventional double glazing cannot match. It allows the fine glazing bars and slender profiles in keeping with the age of a building, while still improving on single glazing. For the most demanding heritage projects, vacuum glazing takes this further, combining the slimmest possible profile with the best performance, which is why the two are often considered together for listed work.
As a rough guide: double glazing suits the majority of homes and renovations; triple glazing is for those chasing the highest thermal performance or building to demanding standards; and vacuum or slim heritage glazing is the answer for period, conservation and listed properties where slim sightlines matter. Because every window is bespoke, we will talk through your property, your priorities and any planning requirements, and recommend the glazing that fits. If you would like to discuss the right option for your home, please get in touch.
