Structural Norms for PV Mounting Systems
Structural Norms for PV Mounting Systems: Fundamentals for Planning and Design
Anyone planning a photovoltaic installation eventually faces one unavoidable topic: structural engineering. The question of which structural norms for PV mounting systems apply and how wind and snow loads are correctly determined decides whether a mounting structure will hold safely on the roof throughout its entire service life. Modules, rails and fixing points form a load-bearing structure that must permanently transfer dead load, wind and snow into the supporting roof construction. This guide summarises the key fundamentals in a factual way and is aimed at planners, installers and operators in a B2B context.
Relevant norms and load assumptions
The structural design of PV substructures in Germany and the EU is based on the Eurocode framework, supplemented by the national annexes of the DIN series. Of particular importance are the action norms for wind and snow loads as well as the general principles of structural design. Material-specific verification norms for aluminium and steel are added on top. The exact norm designation and the applicable edition should be coordinated on a per-project basis with the responsible structural engineer, since editions and national annexes are continuously updated.
The central input parameters of a calculation are:
- Wind load – depending on the wind zone, the building height, the terrain category and the position of the module on the roof (edge and corner zones are more heavily loaded than the centre of the roof).
- Snow load – depending on the snow load zone, the altitude above sea level and the roof pitch.
- Dead load of the modules and the mounting structure.
- Load combinations – the norm requires the superposition of individual actions using defined safety and combination factors.
From load assumption to verification
The load assumptions yield the forces that each component and each anchorage point must absorb. On pitched roofs, this determines, among other things, the permissible spacing of the fixing points. On flat roofs, the focus instead shifts to how much ballast is required to reliably prevent lifting and sliding caused by wind. Verification is typically carried out separately for load-bearing capacity (does nothing break or deform impermissibly?) and positional stability (does the system stay in place?).
One central point: a mounting structure is only as load-bearing as the substrate into which it is anchored. On tiled roofs the loads are guided via roof hooks into the rafters, not into the tiles. On trapezoidal sheet roofs the screw connection in the profile and the structure beneath take on this task; on flat roofs it is the ballast and, where applicable, the roof membrane. The suitability of the substrate is therefore always part of the overall assessment.
Requirements for the mounting structure
A mounting structure that can be designed in accordance with the norms should be available for all relevant wind and snow load zones, use durably corrosion-resistant materials and be documented in a traceable manner. The systems from CLICKWERK in Hamburg are built as component systems that adapt to different roof types:
- T1 Ziegeldach – for clay and concrete roof tiles; the loads are guided via the multi-adjustable roof hook into the rafters without damaging the tiles. A hook spacing of up to 180 cm is possible; according to the manufacturer the system is developed for all wind and snow load zones.
- M1 Trapezblech – a universal single-rail concept for common trapezoidal profiles in commercial, industrial and agricultural construction.
- F1 Flachdach – an aerodynamic, low-ballast elevation system that deflects the wind and thus reduces the wind load; certified to EN 1090-1, manufactured from ZM-coated steel with clamps made of stainless steel 1.4301 (V2A).
The specific permissible loads always result from the project-related structural verification. For the CLICKWERK systems T1 and F1, a structural report can be created with the oneClick planning software; the binding design remains a task of the project's structural engineering.
FAQ – common questions on PV mounting system statics
Which loads must a PV substructure absorb?
Essentially the dead load of modules and structure, the wind load and the snow load. These are superimposed according to the norm in defined load combinations. The exact values depend on location, wind zone, snow load zone, building height and roof geometry.
Do I need a structural verification for every installation?
Assessing load-bearing capacity and positional stability is part of every proper PV plan. Whether a formal, verifiable proof is required depends on the project and local regulations and should be clarified with the structural engineer. For T1 and F1, the oneClick software supports the creation of a structural report.
What distinguishes flat-roof from pitched-roof statics?
On pitched roofs, loads are introduced into the roof construction via fixing points; the focus is on fixing spacing and anchorage. On flat roofs, the priority is positional stability through ballast and – with aerodynamic systems like F1 – the reduction of the attacking wind load.
Planning an installation and need a system that can be designed to the norms? For a complete overview of PV substructures, components and structural design, see our complete PV substructure guide. Get to know our mounting systems, learn more about CLICKWERK or get in touch directly with our team in Hamburg – we will advise you on the right substructure for your roof.