Between too little and too much additional weight lies a narrow margin: If ballasting is missing, the system loses its stability in critical situations. If it is over-ballasted, unnecessary costs, structural problems, and discussions with building authorities may arise.
But how do you find the right balance? Which factors determine the ballasting – and which mistakes occur most frequently in practice?
In this article, we show why precise weight calculation is the key to safe and economical PV fall protection systems – and what planners and installers should pay particular attention to.
Why correct ballasting is so crucial
Ballasting is the core element of any ballasted fall protection system. It ensures that cable and rail systems or single anchor points remain secure even under load. This is not just about pure physics – legal and economic aspects also play a major role.
- Safety aspect: Insufficient ballasting can lead to system failure in critical situations. The consequences range from property damage to personal injury and liability issues.
- Economic aspect: Excessive ballasting means more material, higher costs, and increased roof loads. This often results in additional structural assessments or even reinforcement measures.
- Legal aspect: Only correctly ballasted systems meet building authority requirements and retain their approval. Deviations put insurance coverage and warranty claims at risk.
The basics: additional weight beyond the PV system
All ballasting specifications refer to the additional weight beyond the existing PV system. The modules and the PV substructure already have their own dead weight – the ballasting is added on top.
Depending on the system element, a distinction is made between:
- Corner and end points: They absorb the highest forces and therefore require around 90 kg of additional weight per point.
- Intermediate supports: Here, 60 kg per point is sufficient to safely absorb the longitudinal forces.
- Single anchor points: Also 60 kg additional weight, as they are always used in combination with lifeline- or rail systems.
The principle of module block weights
A stable system setup depends not only on the safety points, but also on the mass of the PV module blocks themselves. This is where the so-called 720/570 rule applies:
- Single module block: at least 720 kg total weight (including modules, PV substructure, and additional ballast).
- Connected module blocks: at least 570 kg per block, as the connection provides additional stability.
Typically, six PV modules together weigh around 110–150 kg. Adding the PV substructure (20–40 kg) results in a remaining requirement of around 550–600 kg of additional ballast per module block.
Common mistakes in practice
Even experienced installers and planners make typical mistakes when it comes to ballasting – often due to routine or time pressure. You should avoid these three pitfalls:
- PV weight counted twice: The dead weight of the PV system is already included – ballasting values always refer to additional load.
- Module block weights ignored: Underweight module blocks compromise stability, even if the safety supports are correctly ballasted.
- Uneven ballast distribution: Incorrect weight distribution can lead to local overloads – particularly critical on green roofs and soft roof structures.
Documentation and approval: not a formality, but a requirement
Every ballasting setup must be clearly and transparently documented – rom calculation and implementation through to annual inspection. This is not only important for liability reasons, but also for building authority approval and insurance coverage.
- Load-bearing capacity verification: demonstrates that the roof structure can safely support the additional load.
- Building authority approval: ensures compliance with the type approval.
- Complete documentation: forms the basis for maintenance and future inspections.
Think economically – plan for safety
Proper ballasting is not a cost factor, but an investment in durability and legal certainty. With smart planning ballast quantities can be optimized without compromising safety:
- Structure the system sensibly: Fewer corner and intermediate points mean less additional load.
- Use standardized concrete slabs: simplifies logistics and installation.
- Plan early: When ballasting is taken into account already during the design phase, later adjustments are rarely necessary.
In the long term, precision pays off – through lower maintenance costs, stable system performance, and reduced risks.
Conclusion
At first glance, ballasting may seem like a purely technical detail – in reality, it is the key to safety, efficiency, and cost-effectiveness in PV fall protection systems. Those who make use of the interaction between structural engineering, standards, and experience can plan systems that deliver what they promise – reliably and in compliance with standards.
Or in short: Correct calculation is half the protection.
What does ballasting mean for PV systems?
Ballasting refers to the application of additional weights to secure PV systems and fall protection systems without roof penetration. It ensures that wind, snow, or other external influences cannot shift or lift the installation.
Why is excessive ballasting problematic?
Excessive ballasting can exceed the permissible roof load, lead to structural issues, and cause unnecessary costs. The goal is a solution that is safe yet economical and complies with structural requirements.
What is the 720/570 rule?
This rule defines the minimum weights for PV module blocks:
- Single module block: at least 720 kg total weight
- Connected module blocks: at least 570 kg per block
This ensures that the system remains stable even under wind loads.
When should ballasting be planned?
Ideally already in the early planning phase. Coordinating the PV system, substructure, structural design, and fall protection helps avoid later corrections and reduces costs.
Does ballasting need to be documented?
Yes – every calculation, every photo, and every ballasting measure must be documented in a traceable manner. These records are relevant for insurance purposes and form the basis for building authority approvals.
