The installation of photovoltaic (PV) and solar systems on existing roofs requires not only thorough technical planning, but also a detailed structural analysis. This verification is essential to ensure that the roof structure can withstand the additional loads and that the system can be operated safely over its entire service life. In this article, we explain the most important aspects of a structural analysis and give you an overview of the key steps and requirements.
Why is the structural analysis required?
Retrofitting a roof with PV or solar systems entails additional loads, including:
- Dead load of the system: The weight of the modules, the substructure and the fastening elements.
- Snow and wind loads: These vary depending on the location, roof pitch and regional climatic conditions.
- Dynamic effects: Vibrations and point loads are caused in particular by wind forces.
A structural analysis ensures that the existing load-bearing structure is not overloaded and thus prevents possible damage such as cracks, deformations or even collapses.
Procedure of the structural analysis
- Survey of the roof structure
First of all, a precise analysis of the existing roof is required. The materials used, the construction method and the condition of the supporting structure are checked. Construction documents such as structural plans or older calculations are often helpful for this. If these are not available, an assessment by a structural engineer may be necessary. - Determination of the additional loads
The loads of the PV system including the substructure as well as the local snow and wind loads are calculated in accordance with the specifications of DIN EN 1991 (Eurocode 1). The roof pitch and orientation also play a role here. - Calculation of the load-bearing capacity
The loads determined are used to check whether the existing construction meets the requirements. Different calculation methods are used for timber, steel or concrete roof beams. In older buildings in particular, it may be necessary to plan reinforcement measures. - Checking the fastening systems
In addition to the load-bearing capacity of the roof, the secure fastening of the system is also crucial. This involves checking whether the fastening points can withstand the forces of wind and snow and do not cause any leaks or material damage.
Special challenges for existing buildings
Existing roofs often have special requirements as they were built according to older standards or may have age-related weaknesses. Common problems are:
- Insufficient load-bearing capacity: Particularly in the case of roofs that were built several decades ago, the dimensions of the supporting structure may not be designed for additional loads.
- Inadequate documentation: Missing or incomplete construction documents make structural calculations more difficult.
- Damage caused by moisture or ageing: This can impair the load-bearing capacity of the structure and may require remedial measures.
In such cases, it may make sense to carry out a thorough inspection and, if necessary, repair the roof in addition to the structural analysis.
Legal requirements and standards
The structural analysis for PV and solar systems on existing roofs is carried out in accordance with the applicable building standards and legal requirements. The main principles are:
- DIN EN 1990 to 1999 (Eurocodes): They regulate the requirements for structural design and load assumptions.
- State building regulations (LBO): These specify when a structural analysis is required and which authorities must be consulted.
- Technical guidelines and manufacturer’s specifications: The manufacturer’s specifications are particularly important for the selection and installation of fastening systems.
Conclusion
A carefully carried out structural analysis is an indispensable basis for the installation of photovoltaic and solar systems on existing roofs. It not only protects the building fabric, but also ensures the safety and durability of the entire system. If you are planning a PV system on your roof, we recommend that you consult an experienced structural engineer or structural engineer at an early stage and provide all relevant construction documents. This means that nothing stands in the way of the safe and efficient use of solar energy.
