The covering system’s theoretical operating conditions, calculated on the assumption of uniformly distributed loads, are not sufficient to ensure the dimensional stability of the roof. In the case of careless foot traffic or excessive tightening of fasteners or because of special events, stress above the endurance of some materials may locally occur.
In the Ondulit multilayer system the value of strength is that one of the steel that forms the internal support. This makes it unbreakable, with no lesions and adequate resistance to foot traffic and overload.
The following table shows the values of tensile strength and expansion coefficients of the most commonly metals used for roofing.