Pitched roof or flat roof? What fastening options are available?

As explained in part 2 of our solar guidebook, the two most common roof shapes on which solar systems are installed are pitched roofs and flat roofs. Using two installation examples, we show the various options for fastening solar installations. We also provide information on the specific details that need to be considered.
 

Assembly example: pitched roof

The existing mounting systems on the market are very diverse, and manufacturers usually have their own individual systems and products. As an example, we will look at two options for fastening the mounting system to the roof substructure of a pitched roof.

Generally, the mounting system comprises the following components:

1. Fastening in the roof substructure, for example with a solar fastener or a roof hook
2. A support structure, such as mounting profiles
3. Module fastening, such as module clamps or insertion rails.

The illustration on the left shows the installation of a solar system with solar fasteners as it would be applied to trapezoidal sheet metal, sandwich panels or corrugated fibre cement sheets. The solar fasteners are screwed directly into the steel or timber roof substructure. The mounting rails that support the solar panels or solar collectors and to which they are fixed with the help of module clamps can then be attached to the solar fasteners.

In contrast, the illustration on the right shows a tiled roof, as found in many residential buildings. In this case, roof hooks are used as connection between the roof substructure and the mounting rails. These roof hooks are usually attached to the rafters with flat head screws. As with the solar fastener, the roof hooks are used to fasten the mounting rails, to which the panels are fastened in turn.

For trapezoidal profiled sheets and sandwich panels, there is the alternative option of screwing the mounting rails into the roofing in addition to fastening them in the roof substructure. With these systems, so-called short rails or trapezoidal sheet flashings are fastened to the trapezoidal profiled sheet or the cover shell of the sandwich panel using thin sheet metal screws. Once the short rails have been installed, it is possible to either attach the modules or collectors directly to them using module clamps or, alternatively, to install an additional longer rail into which the modules can be inserted. In this system, the loads are transferred directly into the trapezoidal profiled sheet. Therefore, it is important to mention that the trapezoidal profiled sheet must absorb the entire load at the points where the short rails are mounted.

Assembly example: flat roof

In addition to pitched roofs, flat roofs are particularly well suited for installing a solar plant. In this case, the installation can be planned independently of the roof pitch and orientation, allowing the solar modules to be optimally aligned.

The ballasted systems used on flat roofs are not fixed on or in the roof. The system is secured only by its own weight or additional load such as gravel in mounting troughs, concrete slabs or similar. Ballasted systems cover the largest share of flat roof mounting systems and are usually aerodynamically optimised. This means that the systems have been developed to minimize air resistance. This in turn reduces the required ballast and also eases the load on the roof. It must always be checked in advance whether the roof structure is designed to have a solar installation mounted.

The next part of the solar guidebook will take a detailed look at the structure and fields of application of the solar fastener and explain the main differences between it and the conventional hanger bolt. What are the benefits of the fastening element and what special options does it offer?