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As leading double glazing specialists in the West Midlands for over 40 years, we’re often asked about window energy efficiency and U-values.
In this comprehensive blog, we’ll explain everything you need to know about U-values and why they’re crucial for your home’s thermal performance.

A U-value measures the rate of heat transfer through building materials, including glazing. Put simply, it tells you how effective your windows are at preventing heat loss. For double glazing in the UK, U-values are measured in watts per square metre kelvin (W/m²K). The thermal transmittance through your windows directly impacts your home’s energy efficiency and comfort. With U-values, the lower the number, the more energy efficient the windows are.
With rising energy costs, understanding U-values is more crucial than ever. Windows with lower U-values provide better insulation, resulting in significant energy savings. When your windows have good thermal resistance, they maintain a more consistent indoor temperature, which is important during the winter but also in the summer. This means less energy consumption and a more comfortable living space throughout the year.
Current UK building regulations require replacement windows to achieve a maximum U-value of 1.4 W/m²K for double glazing. At Leamore Windows, our high-performance double glazed units meet and often exceed these standards. We understand that compliance isn’t just about meeting minimum standards – it’s about providing the best solution for your home’s energy efficiency.
Double glazed windows achieve thermal efficiency through several key components working together to create an effective insulation system. The primary elements include two panes of glass separated with a high-quality spacer bar and filled with argon gas, which provides superior insulation compared to air. The addition of low-E glass coating reflects heat back into your home, improving the window’s thermal performance.

The overall performance of your double glazing depends on multiple factors that work together to determine its U-value. Frame material plays a crucial role, with modern uPVC frames offering excellent thermal resistance. The type of glass used, particularly when improved with thermal coatings, can significantly impact performance, and the width of the gap between panes must be precisely calculated to optimise thermal efficiency.
As manufacturers of our own double-glazed units since the 1980s, we bring unparalleled expertise to every installation. Our manufacturing process incorporates the latest technological advances in thermal efficiency, ensuring optimal performance across our range. Each unit is carefully constructed to maximise energy efficiency while maintaining structural integrity and aesthetic appeal.
With growing concerns about sustainability, choosing windows with optimal U-values contributes positively to the environment. Better insulation means less energy consumption, which directly reduces your carbon footprint.
Investing in high-performance double glazing isn’t just about immediate benefits; it’s also about future-proofing your home. As energy costs continue to rise and environmental regulations become stricter, having efficient glazing becomes increasingly important. The long-term savings on energy bills can make quality double glazing a cost-effective choice for homeowners looking to improve their property’s energy performance.
High quality glazing will improve the value of your property, offsetting at least some of the initial investment.
While standard double glazing offers excellent thermal performance, triple glazing windows can achieve even lower U-values. At Leamore Windows, we offer both options to suit different requirements. Triple glazing adds an additional pane of glass, providing better insulation.
When choosing the right glazing for your home, experience and expertise matter. As a family-run business established in 1983, Leamore Windows has been at the forefront of window manufacturing and installation in the West Midlands for over 40 years. Our journey began with two brothers who envisioned transforming the double-glazing industry’s reputation through quality and exceptional customer service.
Unlike many other companies, we manufacture our own double-glazed units in our factory, giving us complete control over quality and lead times. This in-house manufacturing capability allows us to provide consistent, high-performance products that excel in both thermal efficiency and durability.

Understanding U-values is crucial for making informed decisions about your home’s glazing. At Leamore Windows, we’re committed to providing energy-efficient solutions that meet and exceed building regulations and help reduce your energy consumption. With our expertise in manufacturing and installation, we ensure every customer receives the perfect balance of thermal efficiency, durability, and value.
We offer our double and triple glazing on a wide range of products. From our casement windows and flush sash windows to our glazed extensions.
We have a huge showroom with two floors full of our products, ready for you to see and use. You can find this at Reaymer Close, Bloxwich, WS2 7QZ.
You can call our friendly team on 01922 473 737, email us at info@leamorewindows.com or use our online contact form.
We hope you now understand U-values and energy efficiency better, enabling you to make an informed decision. With over four decades of experience in the West Midlands, we’re here to help you at every step of your home improvement project.
We look forward to hearing from you.
The typical U value range for modern double glazing is between 1.2 to 1.6 W/m²K, depending on the quality of the materials used and the design of the window.
U values for double glazed windows are calculated by measuring the rate of heat transfer through the window, taking into account factors such as the type of glass, the spacing of the glazing, and the frame materials. The calculation is expressed in watts per square meter per degree Kelvin (W/m²K).
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