Whether you’re replacing the windows in an existing property or are project managing a new build, windows are one of the most important things to consider. It’s a given that they provide a source of natural light. But the type of windows you choose can also have a significant impact on the energy efficiency of a building.
We’re not talking about regular versus sash windows here. What we’re referring to is how much heat is lost through the windows. This is expressed as a U-Value. To find out what a U-Value is, why it matters, and how it can affect your heating bills and carbon footprint, read on.
What are U-Value Windows?
The U-Value of a window is a measure of its thermal efficiency. U-Values indicate how effectively energy is transferred. In simple terms, a window’s U-Value tells you how much heat is likely to be lost through it.
Calculating the U-Value of a window involves dividing the rate of heat conduction through a square metre by the temperature difference on either side. In the case of sash windows and other types, this means comparing the inside and outside temperatures to work out how much heat is being transmitted through the glass.
U-Values are not only applied to windows. Many parts of a structure can also be given a U-Value, including the walls, the roof, the floor, and of course the doors.
How U-Values are calculated
U-Values are expressed as watts per square metre. For example, a sash window with a U-Value of 1.4 transfers 1.4 watts of heat per square metre, for each degree of temperature difference on either side.
Ug and Uw values
If you want to compare U-Values, it’s important to know that these can be expressed in two ways. The Ug value only applies to the glass, whereas the Uw value includes the frame in addition to the glass.
Factors Affecting the U-Value
The U-Value of a window is influenced by a range of factors. These include the type of glass, the sort of gas and distance between the panes, the number of panes present, how energy efficient the spacer bar is, and the frame materials.
High vs Low U-Values
So should you be looking for a low or high U-Value? In this instance, a low U-Value is better, as it means less heat will be lost. A sash window with a 1.2 U-Value, for instance, will transmit less heat than one with a 1.4 rating, therefore providing more effective insulation and keeping the building warmer.
Glass vs Frame
The Uw value for the whole window will usually be higher than the Ug rating of the glass alone. This is because the frame, spacer bar, and seals transfer more heat than the glass. Window glass is more energy efficient than the frame and other components surrounding it. In other words, more heat will be lost through the frame than via the glass.
Large vs Small windows
Larger windows tend to be more energy efficient than smaller ones. Remember that U-Values are expressed per square metre. As there is a higher ratio of frame to glass, a smaller window loses more heat than a larger one. This, however, is per square metre, rather than in an absolute sense.
Good vs Bad U-Values
Whether you’re looking to replace or install glazing such as sash windows, it makes sense to look for as low a U-Value as possible. Current Building Regulations require a U-Value of 1.4 or lower for windows. This is likely to fall in the future.
For comparison, single glazed windows may have a U-Value as high as 4.8. This rating might drop to 2.4 for old double glazing. U-Values as low as 1.2 are typical for double glazing with argon glass, such as K Glass. Triple-glazed windows may have a U-Value of under 1, such as 0.95 or 0.8.
Impact of U-Value Windows
Energy Efficiency
If you want the most energy efficient windows, look for a low U-Value. A lower wattage per square metre means less heat is lost. This, in turn, means that products such as sash windows with a low U-Value are more energy efficient.
Heating Bills
So, if low U-Value windows are more energy efficient, it stands to reason that they can help to keep your heating bills down. Improved energy efficiency retains more heat inside the building, so you won’t need to use as much power to stay warm.
Carbon Footprint
Due to their improved insulating properties, low U-Value windows are also better for the planet. Better energy efficiency means you’ll use less gas or electricity to heat the building, thereby reducing your carbon footprint.
Windows from Woodcock Sash Windows
At Woodcock Sash Windows, we specialise in crafting bespoke box sash windows and casement windows designed to enhance both the performance and aesthetic of your property.
Whether you’re upgrading to energy-efficient glazing, restoring your traditional windows, or in need of expert window repairs, our team ensures a solution tailored to your needs. Experience the perfect blend of timeless design and modern efficiency with Woodcock Sash Windows – where quality and craftsmanship meet innovation.
For more information and to get a quotation, please get in touch with us today.