The U-Value of your windows plays a crucial role in the performance of your property, from improving its market value to reducing your energy bills. If you already have high-quality timber windows installed, you're already on the right path, but paying attention to U-Values ensures you maximise every benefit available.
What Is a U-Value?
A U-Value measures how effectively heat is transferred through a window or door, including the frame, sash, and glazing. The lower the U-Value, the better the window or door retains heat within the building — an essential feature for both comfort and energy savings, especially during colder months.
What Is the Best U-Value for Your Windows?
When considering windows for your home, the lower the U-Value, the better.
In line with updated Building Regulations, new timber windows must achieve a U-Value below 1.4 W/m²K to meet current energy efficiency standards.
At Mumford & Wood, our timber windows are fitted with thermally enhanced insulating glass units, achieving U-Values as low as 1.1 W/m²K — significantly exceeding regulatory requirements and ensuring superior thermal performance.
For new buildings, U-values are assessed across all components of the building envelope and contribute towards the Standard Assessment Procedure (SAP) calculation, which ultimately determines the Energy Performance Certificate (EPC) rating upon completion.
How Is a U-Value Calculated?
Several different factors are measured to determine the overall U-value for a window:
- Ug Value: The thermal performance of the glass.
- Uf Value: The thermal performance of the window frame.
- PSIG: The thermal performance of the spacer bars between panes.
These combined factors provide a comprehensive view of how energy-efficient a window or door unit will be.
U-Values for Timber Windows
Timber is a naturally insulating material, providing a significant head start in terms of thermal efficiency. However, the overall U-value will also depend heavily on the glazing units chosen.
Mumford & Wood timber casement and sash windows typically achieve U-values of around 1.1 W/m²K, thanks to the use of thermally enhanced insulating glass, which is almost twice as effective as standard glazing units.
It’s important to note that while Building Regulations updated the required U-Value for windows to 1.4 W/m²K in June 2022, timber windows have been granted an extended transition period for compliance. Choosing a manufacturer that already meets or exceeds these standards provides future-proof peace of mind.
Choose Timber Windows Designed for Energy Efficiency
At Mumford & Wood, we specialise in the creation of beautifully engineered, sustainable timber windows and doors. Our commitment to high-quality materials and meticulous craftsmanship ensures that every product not only enhances the aesthetic of your home but also delivers exceptional thermal performance for years to come.
Explore our brochure or contact us today to find out more about our collection of bespoke timber windows and doors.
