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Friction coefficient determination for flat roof installations

Friction coefficient determination for flat roof installations made easy

Installation on a roof must not pose a hazard and must guarantee the safety of people in the vicinity at all times. This requires a sufficiently strong connection between the substructure and the roof. With classic mounting on a saddle roof, safety is guaranteed by a fixed connection between roof hooks and rafters. In flat roof installations, on the other hand, this must be achieved solely by friction.

The static friction depends on the weight of the entire system (modules + substructure + ballasting), as well as on the interaction of the existing materials (roof cladding + protective mat of the assembly system). This results in a so-called coefficient of friction (formula symbol µ), which is required for the static calculation of the design programs, for example from K2 Systems. It is therefore imperative for safety reasons that the conditions on site are determined correctly!

Procedure for on-site testing


To determine the coefficient of friction, a so-called Königsberg friction block is used, with which the value can be determined quickly and easily.

Bildquelle: K2 Systems

It includes a precision spring balance and a friction block, which can be fitted with various everyday surfaces through recesses. The test weight is exactly 1 kg to simplify the subsequent calculation of the coefficient of friction.

Once suitable surfaces have been selected, the block on the spring-loaded scale is pulled over the surface to be tested. The coefficient of friction is calculated by dividing the displayed value by the weight of the test block (1 kg).

Once suitable surfaces have been selected, the block on the spring-loaded scale is pulled over the surface to be tested. The coefficient of friction is calculated by dividing the displayed value by the In this case the value is 300g = 0.3kg. This corresponds to a coefficient of friction of:

µ = 0.3kg / 1kg = 0.3

This test must be carried out on site at several positions (edge, corner and middle area) as well as in wet and dry conditions. Just under all conditions that could actually occur in everyday life. The lowest value is used as the basis for further calculation.

This value should be properly checked by default in all circumstances, as negligent action can cause serious damage and consequential damage and, in the worst case, endanger human life.

The complete test set can be purchased from Krannich Solar under article number #20020.eight of the test block (1 kg).

02.05.2018 14:57
by Maik Wünsche

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