If you've ever shopped for new windows and doors, you'll have seen "U-value" everywhere, sprawled across product pages and shown off proudly. But what on earth is it, and is a high or low number better? Here's the plain-English guide.
U-value measures how easily heat passes through a material, essentially, how good it is at retaining heat. It's measured in Watts per square metre per Kelvin (W/m²K), and the crucial rule is: lower is better. A low U-value means heat struggles to escape; a high one means it pours through.
Some real numbers help. A typical insulated house roof achieves around 0.11 W/m²K. A Guardian Warm Roof on a conservatory can achieve as low as 0.18, remarkably close to house-roof performance. Old single glazing, by contrast, can be worse than 5.0, which is why single-glazed rooms feel cold near the windows: heat is streaming out.
When you're comparing products, U-values let you cut through the marketing, the numbers are measured the same way everywhere, so you can compare fairly between brands, materials and quotes.
We'll happily explain the numbers on any quote, including ours. That's what honest advice looks like. Get in touch with any question.