Photovoltaics is one of the most effective ways to make buildings more energy-independent and meet rising electricity demand. More and more new-builds plan PV systems in from the outset and the range of retrofit solutions for renovation projects keeps growing too. Depending on location, orientation and roof pitch, different mounting methods come into play: roof-parallel, slightly tilted, or steeply tilted and rotated relative to the actual roof pitch.
The decisive question for architects and planners, however, is this: which solution is technically the best, and which roof substrate will carry it reliably for the long term?
The answer lies in the standing seam roof. It can be combined with the BEMO-AKKORD rail system without penetrating the watertight layer at all. The rails are seamed directly onto the roof, transfer linear loads rather than point loads, and work for roof-parallel, tilted, and rotated tilted installations alike.
On-Roof Photovoltaics: Opportunities and Common Pitfalls
On every PV system, the roof covering is the connecting element between the modules and the load-bearing structure. On-roof solutions account for the largest share of newly installed PV systems. Here, substructures are fitted retroactively or already during construction, and subsequently carry the PV modules and the cabling.
Planning requires close attention, because mistakes happen faster than you’d think. Correctly calculated structural spacing and dimensioning of the fixing points are essential, as is accounting for the thermal expansion of the substructure rails. Choosing the right system is just as critical: it has to be compatible with the roof covering and, ideally, bring it no disadvantages whatsoever. A PV system is only ever as good as the roof beneath it, and that roof has to keep performing reliably for decades.
Why the Standing Seam Roof Is the Ideal Base for Photovoltaics
For a permanently watertight building envelope, the roof of choice should do without screw fixings, adhesives and cross joints. Every penetration makes a roof more vulnerable and creates a potential source of leaks. This is exactly where the industrially manufactured standing seam roof comes in. Its advantages for PV on-roof mounting at a glance:
- Carries general building authority approval and can be used from as little as 1.5 degrees of roof pitch
- Can be laid in any panel length, with no cross joints at all
- No screws whatsoever in the watertight layer, eliminating a classic weak point
- Linear rather than point load transfer for on-roof systems
- A life expectancy of at least 50 years
Combined with a matching substructure system that consistently builds on these properties, the connection to the roof is made entirely without screw fixings and without damaging the roof covering. The roof system retains its function in full, and the photovoltaic installation keeps working reliably for decades.
The BEMO-AKKORD Rail System: Penetration-Free and Structurally Sound
The BEMO-AKKORD rail system, which carries general building authority approval, is seamed directly onto the standing seam panels. It absorbs the thermally driven movements of the roof and slides along with them, without any constraint or restriction of the roof beneath. On new builds, the rail spacing can be matched perfectly to the module size, further improving the economics of the overall system.
A key structural advantage of the AKKORD rails is that they generate linear loads rather than point loads. These are precisely matched to the roof system below, allowing the structural design to be pushed to its full potential and enabling large spans. Custom width production also allows the roof covering and the PV module width to be aligned with millimetre precision.
Three Mounting Variants, One Principle
The AKKORD system works not only for roof-parallel installations but equally for tilted and rotated tilted constructions. The connection to the roof stays identical across all variants: seamed rails form the base, entirely without screw fixings and therefore without a weak point. Depending on requirements, cross profiles and tilt frames are then mounted on top. Orientation, system size and roof pitch determine the structural dimensioning of the substructure, which is then planned to fit precisely and delivered as a kit.
A mounted PV array on BEMO-AKKORD rails during installation
Installation of PV modules on BEMO-AKKORD rails in a roof-parallel orientation
PV mounting solution with curved BEMO-AKKORD rails for arched roof surfaces
PV mounting solution perpendicular to the standing seam direction on a metal roof
PV substructure with additional cross rails on a standing seam roof
Conclusion: Photovoltaics Needs the Right Roof
Whether roof-parallel, tilted, or rotated relative to the roof pitch: a photovoltaic system is only as durable as its substructure and the roof it rests on. With the standing seam roof and the BEMO-AKKORD rail system, architects and planners have a solution that requires no penetration of the watertight layer, is structurally sound, and keeps working reliably for decades. A system that convinces for the long term, sustainably.
Further Reading
- BEMO-AKKORD rail: technical data sheet for the mounting system
- Standing seam roof & roof covering: system overview
- On-roof solutions for metal roofs: all on-roof systems at a glance
- Reference: photovoltaic standing seam roof for aircraft manufacturer Pilatus
