Thermal Transmittance is a Key Parameter in Glass Performance

Keeping a conservatory warm in winter and cool in summer is an important consideration. And the U-value of the glass plays an important role.

Thermal transmittance describes heat flow through a solid substance, and in building materials, this is defined by a property called the U-value. We all know that in an old conservatory that has stood for years, you are likely to feel freezing cold in winter, while in the height of summer, you feel as if you could cook an egg by cracking it on the floor. This is because the thermal transmittance, or U-value is high, and heat comes in through the glass in summer, and goes the other way just as quickly in winter.

Clearly, then, understanding the U-value for the different types of glass you might choose for your new conservatory is an important consideration. Here, we look at U-values in a little more detail, and find out how some of the most popular windows stack up.

Measuring the U-value

The U-value describes how much thermal energy, or heat, is transferred through one square metre of a given substance when there is a temperature difference of 1K (scientists use Kelvins, which are conveniently the equal to Celsius) on either side. Thermal energy is measured in Watts (W) so the unit of measure for U-values is W/(m2K).

Some typical U-values

From a homeowner’s perspective, the rule you need to remember when it comes to U-values is “the lower the better.”

To give you a feel for what is a good or bad U-value, here are some typical U-value examples:

  • Traditional single glazed window: 5.7 W/(m2K)
  • Traditional double glazed window: 3.3 W/(m2K)
  • Advanced double glazed window: 1.2 W/(m2K)
  • Well insulated roof: 0.15 W/(m2K)
  • Poorly insulated roof: 1.0 W/(m2K)
  • Well insulated wall: 0.25 W/(m2K)
  • Poorly insulated wall: 1.5 W/(m2K)

Modern conservatory glass and U-values

The above examples show just how big a difference the glass can make when it comes to thermal insulation. Suddenly, that complaint that an old conservatory is either freezing cold or boiling hot for 50 weeks of the year starts to make sense if it is single glazed with traditional glass.

The U-values of advanced double and triple glazing are a world away from these old fashioned materials.

At Caulfield conservatories, our Solarlux windows and bi-folding doors do not just look modern and sophisticated, they also offer astonishing levels of efficiency and comfort when it comes to thermal conductivity. The manufacturers quote a U-value of just 0.8 W/(m2K).

Meanwhile, our Internorm glass products are best in class. With 80 years of innovation behind them, Internorm are renowned as one of the top quality glass manufacturers in the world. Their products have thermal conductivity properties that are an industry benchmark, quoting a U-value of 0.62 W/(m2K).

By using these industry-leading materials, Caulfield conservatories provide a living space that is energy efficient, and most important of all, is a comfortable place to be all year round, whatever the weather.