Cracking noises are mainly caused by sunlight or cooling of light roof or wall elements made of metal, whereby these elements themselves do not produce any noise.

Due to the relatively low local strength, absolutely 'solid' connections are difficult to achieve in wooden substructures, e.g. between trusses and the suspended purlins or connections between supports and wall transoms.

In this respect, slight displacements in these connection areas are to be expected with corresponding changes in length and thus stresses, e.g. due to thermal stress caused by solar radiation on the fixed cladding components.

If such displacements do not take place without friction, the stresses are discharged jerkily with cracking noises.

Due to the stable connection of components with the substructure via screws, temperature stresses arise which are compensated either by deformation, sliding displacement or, in case of correspondingly strong friction between component and substructure, by jerky displacement and a corresponding noise.

With multi-layer building systems, such as a roof system consisting of two metal skins, thermal stresses of the outer skin within the roof system are reduced via the relatively flexible intermediate construction made of Z-profiles, so that cracking noises occur less frequently and are also quieter.

In contrast, sandwich panels with a PUR core and metal face sheets have a 'shear stiff' connection between the outer and inner shells, which means that internal stress relief is only possible to a limited extent and noise is more frequent.

Due to the relatively low mass of the outer sheet of the sandwich panel, it heats up or cools down quickly, causing dilatations or contractions.

Light exterior colors have a more favorable effect due to the lower heating of the outer shell, aluminum outer shells have a less favorable effect due to the thermal expansion coefficient which is twice as high as that of sheet steel.

Since a sandwich panel, in addition to the change in length, also deforms convexly like a BI metal when heated externally, there are additional stresses in the substructure due to twisting of the purlins and transoms and additional lifting forces on the central supports of the purlins or transoms. In addition, a supporting structure made of wood is a much better resonance body than one made of steel or reinforced concrete, and noise is amplified as a result.

Cracking noises cannot be reliably avoided with such relatively inexpensive metal roof and wall construction systems, so must therefore be regarded as normal and are not a defect.

Only in the case of high-quality curtain walls, which cost between approx. EURO 600 and EURO 3,000 per m2, do cracking noises represent a defect.

These noises are prevented by elaborate, three-dimensionally tension-free sliding connections or by mounting the fastening points in rubber-elastic profiles.

Netphen, March 2001
Addition, May 2007

Write a comment