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U-value

WHAT IS HEAT LOSS AND WHY DOES IT MATTER?

The importance of U-Value

The U-factor or U-value is the overall heat transfer coefficient that describes how well a building element conducts heat or the rate of heat transfer (in watts) through one square metre of a structure divided by the difference in temperature across the structure.

The elements are commonly assemblies of many layers of components such as those that make up walls / floors / roofs etc. These values measure the rate of heat transfer through a building element over a given area under standardised conditions.

The usual standard is at a temperature gradient of 24° C (75° F) at 50% humidity with no wind. It is expressed in watts per meter squared kelvin (W / m²K). A lower U-factor / value indicates a greater reduction of heat transfer.

Impact due to substructure

Today’s targets, requirements and standards relating to the efficiency and sustainability of buildings inevitably demand new, innovative solutions, also for facades.

Various studies, including tests carried out by the Swiss Federal Laboratories for Materials Science and Technology (EMPA — Eidgenössische Materialprüfanstalt) have shown, for example, that the requirements of the «Passivhaus» standards can no longer be met by facade substructures constructed only from aluminum.

Through use of brackets such as the Hilti MFT-FOX VT / HT, designed to eliminate thermal bridging, not only can the thickness of the insulating layer be reduced, but an up to 40% better U-value can be achieved compared to metal structures.

The diagram compares standard aluminium substructures to substructures designed to reduce thermal bridging.

The isothermal image clearly shows the uniform heat distribution.
The result is a facade with virtually no losses due to thermal bridging.