U Values for Different Types of Windows

Different glass windows have a different set of u values. Some of the most common glass window u values are listed down below:

Window Type	Average U Value
Single Glazing	5.2 W/m2K
Uncoated Double Glazing	2.7 W/m2K
Coated Double Glazing	1.2 W/m2K
Triple Glazing	0.8 W/m2K
CU.In Glazing	0.4 W/m2K

Selecting the best glass for your windows can be tricky, especially when numerous glass options are available in the market. However, there are certain factors you should be mindful of before making the final choice.

One such factor is the U value of the glass. Most certainly, the majority of people do not know what is u value of glass. Therefore, this blog will enlighten you on the basics of u value, why it is important and which glass has what u value. So let us begin!

What is U Value?

U value, in simple terms, is the measurement of heat loss in a glass and the rate at which the heat is lost. It indicates the performance of the glass based on its ability to retain heat and not let it pass through the windows.

U value is typically measured in Watts per square metre Kelvin or W/m2K. In layman’s language, the lower u value, the better the thermal performance of the glass.

How are U Values Calculated?

Once you are familiar with what is u value, the second question arises about how u values are calculated. Calculating u value of glass is simple. A mathematical formula is used to calculate u value of the glass.

You need to find the reciprocal sum of the thermal resistances for each material making up the building element. Remember, the internal and external faces of the glass also have certain resistance that needs to be added to the formula. Accordingly, u value for different glass types is calculated, and their quality can be analysed.

What are the Minimum U Values for Windows?

Glazing in the windows can have highly variable u values. Traditionally, double-glazed windows used spacer bars around the sealed unit with air in the left-out space. These kinds of glasses usually had a higher u value than modern glasses.

Today’s glazing, whether double or triple glazing, leverage a low-emissivity or Low E glass coating with warm-edge spacer bars and gases such as Argon and Krypton in between the glass. All new or replacement timber windows, aluminium windows or PVCu have a minimum U-Value of 1.6 W/m2K or less.

Here are some of u values measured for an average household:

Property	Insulation	Approximate U-Value
Roof	✔️	0.5
Roof	❌	2.4
Cavity Wall	✔️	0.7
Cavity Wall	❌	1.7
Floor	✔️	0.7
Floor	❌	0.9
Old single glazed window	None	5.8-5.9
Old Double-Glazed window with air in between	None	2.8-3.0
Double glazed units with argon gas	None	1.2-1.2
Triple glazed units with argon gas	None	0.9-1.0

Single Vs. Double Vs. Triple Glazing Windows: What is the Difference?

Now that we are a little familiar with different types of glass windows and their u values, let us break them down for a more comprehensive study.

Single Glazing U Value

This is the most basic form of glazing. It consists of one pane of glass in the window. Generally, single glazing windows were used in traditionally styled homes. The average single glazed window u value is approx. 5.2 W/m2K.

Benefits

• It is the most economical option for a glass window.

Drawbacks

• It has a higher u value compared to the other options.
• Current building regulations advise having a window with a U value of no more than 1.6W/m2. This means single-glazed windows do not fall anywhere near the prescribed window measurements.

Double Glazing U Value

It is one of the most prevalent forms of glazing used in the UK. It comprises two panes separated by a spacer bar. The gap between the windows traps the heat and does not allow it to escape from the windows.

Double glazing glass has good thermal and acoustic glass window insulation properties, making it highly suitable for standard modern properties. The average u value of double-glazing window is approx. 1.6 W/m2K.

Benefits

• It offers great thermal and acoustic insulation, which keeps the home warmer for a longer duration.
• It is a cost-effective option and is energy efficient.

Drawbacks

• Difficulty in installation, especially in the conservation areas, as it needs to blend with the surroundings to perform its function perfectly.

Triple Glazing U Value

It is one of the latest and most advanced types of window glazing. Triple glazing is highly like double glazing but is more efficient in providing thermal and acoustic insulation. It uses the same concept as double-glazed windows.

Three panes are installed, and the heat is trapped in between the panes to keep the glass and home warmer. The average triple glazed windows u value is approx. 0.8 W/m2K.

Benefits

• It offers the highest level of thermal and acoustic insulation.
• It significantly saves energy and helps reduce heating bills.

Drawbacks

• It is an expensive form of window glazing option.

C.U.in Glass U Value

This is one of the most prominent glass options that delivers exceptionally high performance. It is a lightweight glass with triple glazing glass properties and is available at a more affordable price.

The glass consists of Krypton gas in between the panes and includes an invisible suspended film, which lowers the thermal conductivity, offering better overall performance. The average C.U.in glass u value is approx. 0.4 W/m2K.

Benefits

• It has 30% less weight than triple glazing windows.
• It enhances the thermal performance of the glass.
• Sustainable using lower CO2 footprint from manufacturing to lifespan.
• Eco-friendly, resulting in lower fossil fuel energy usage.
• It is extremely easy to install.
• It is an energy-efficient option.
• It delivers the best results compared to all other alternative options.

Drawback

• It is a very similar cost to Triple Glazing and occasionally slightly higher but includes a host of benefits.

Which One to Choose: Single, Double, Triple, or C.U.in Glass?

All these glass types have their merits and demerits. However, in our opinion, if we analyze the overall performance and price of the glazing, C.U.in glazing seems to be the most viable option. It is lightweight, cost-efficient, sustainable and offers unmatched performance. Besides, C.U.in is known for their exceptional user service, which is the icing on the cake. So take the first step today, visit our website to see the benefits, and reach out to the C.U.in team if you need more detailed information.