How much heat is transferred from the interior to the exterior when using ETICS anchors?

ETICS anchors are potential thermal bridges and may promote heat transfer in an insulated component, depending on the quality of the anchor. By using premium anchors with low heat conductivity, you may not require further insulation measures.

Together with the insulation material used, ETICS anchors have a significant influence on the heat loss through house facades. The amount of heat that anchors transfer from inside a building is measured at specific points using the Chi value. The basic principle is that the smaller the Chi value of an ETICS anchor the lower the impact of an anchor on a component’s U-value. Furthermore, the number of anchors per square metres also affects the value. A low number has a positive impact on the U-value.

The U-value is a specific value that compares the insulation properties of components. It indicates how much heat per square metres flows through a component. A low U-value gives an indication that the components used allow for little heat to transfer from the interior to the exterior. Consequently, a building stays warm for a longer time.

In Germany, the German technical authority Deutsches Institut für Bautechnik (DIBt) has carried out a recalculation of the role anchors play in thermal bridging, revising the respective tables in 2016 as the quality both of insulation materials and anchors has improved drastically in the past few years.

If anchors with a Chi value of 0.001 to 0.004 W/K are used, the component’s U-value must be revised upwards, if the cumulative thermal bridges of a component’s anchors deteriorate by more than 3%. The number of anchors per square metre has therefore been newly limited in Germany by the DIBt with regards to U-value calculations.

A case example shows: At a U-value between 0.15 and 0.25 W/(m2 * K) a component’s U-value deteriorates by up to 13% to between 0.17 and 0.27 W/(m2 * K) when using 10 anchors per square metre of the 0.002 W/(m2 * K) Chi value class. As a consequence, the heat loss caused by the ETICS anchors would have to be compensated by increasing the insulation thickness.

If, on the other hand, anchors with a Chi value of 0.000 W/K are used, the maximum number of anchors per square metre can be used, independent of the insulation material’s heat conductivity and thickness without having to correct the façade wall’s U-value.

Especially when using thick insulation materials and high-performance insulation materials, it is strongly advised to use ETICS anchors free of thermal bridging with a Chi value of 0.000 W/K.

Find out why the use of anchors with a Chi value of 0.000 W/K furthermore helps in avoiding bright anchor marks in the article How to prevent your insulated façade from getting the measles.

The bottom line is that in Germany a component’s U-value is revised upwards, therefore classifying the insulation performance as lower if anchors with a Chi value of 0.001 to 0.004 W/K are used. This means that the use of anchors with a Chi value of 0.000 W/K is advantageous also against the backdrop of the DIBt 2016 regulation. Since they do not cause thermal bridging they need not be disclosed when calculating the U-value.

Incidentally, as opposed to Germany, regulators in Austria and Switzerland currently do not ask for separate verifications.

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