U–Value is the measure of the rate of heat loss through a material. With glass the aim is to achieve the lowest U–Value as possible, since the lower the U–Value, the less heat will escape from your conservatory when all the doors and windows are closed.
Technically, U–Values are calculated as the amount of heat lost through one square meter of glass for every degree difference in temperature either side of the glass.
In descending order, these are typical U–values for glass:
- Single–glazing 5.6
- Double–glazing with 16-20mm gap 3.0
- Triple–glazing with 16-20mm gap 2.2
- Double–glazing with 16-20mm gap low–e coating 1.6
- Double–glazing with 16-20mm gap low–e coating and argon filled 1.4
- Double–glazing with 16-20mm gap soft coat low–e coating and Argon filled 1.2
- Double–glazing with 16-20mm gap SmartGlass® Ultra86 Solar Control roof glass with soft coat low–e coating and Argon filled 1.0
- Double–glazing with 16-20mm gap SmartGlass® W Ultimate Solar Control frame glass with soft coat low–e, multiple coating and Argon filled 1.0
- Triple–glazing with 16mm gap multiple low–e coatings, Argon filled, 44mm overall thickness 0.8 (typically 75% more cost
- Triple–glazing with multiple low–e coatings and Xenon filled 0.7 (typically 5-6 x the cost)
To keep your heating bills low, you will need to invest in the lowest U–Value glass. There will be a point at which the investment reaches the point of ever diminishing returns, this will depend on the total volume of glass, how much you pay for your energy, as well as how much time you plan to spend in your conservatory or orangery in the winter months. A glazing or conservatory consultant should be able to help you with these calculations.