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U Value

U-value is used to express and calculate the amount of heat loss through structural elements, measured in watts per square metre. It forms part of everyday specification and construction under building regulations, especially as environmental rules become more stringent to make buildings more energy efficient, residential or commercial. 

The TF range offers a better U-value in comparison with standard glass. The TF30 has two air chambers, with one cavity and four glass faces. TF60 has three air chambers and two cavities with six faces. 

TF U-value characteristics

TF30: U-value = <2.0 W/m2 0C

TF60: U-value = 1.6 W/m2 0C

These are all tested and assessed by the CEBTP of France in conjunction with La Rochere (TF manufacturer). Test data document reference B232.3.047.

U-value calculations are based on construction with Rods & Mortar. Using a premade factory-controlled mortar ensures a constant, stable and calculable U-value. Using sand and cement will increase the heat loss. 

An important part of specifying glass blocks for U-value is the perimeter opening and ensuring it is sufficiently insulated to assist against cold-bridging. Ensure expansion joints are not restricted and are flexible.


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