Solar Roof Mounting Systems

Solar roof mounting systems (racking) attach photovoltaic panels to a roof, hold them at the desired angle, and transfer wind, snow and dead loads into the building structure. The choice of system affects the roof's waterproofing, structural load and long-term maintenance.

Pitched roofs

On sloped roofs, arrays are usually mounted parallel to the roof surface with a gap of a few centimetres for airflow and drainage.

• Rail-based systems use aluminium rails fixed to the roof with brackets (feet or hooks). Brackets are fastened into rafters or the deck and sealed with flashing designed for the roof covering: flashed mounts for shingles, tile hooks or replacement flashing tiles for tile roofs.
• Rail-less systems fix panels directly to individual mounts.
• Seam clamps on standing seam metal roofs grip the raised seams, avoiding holes in the panels.
• Tile roofs often need tiles cut or replaced at each hook so the tile can sit flat and shed water.

Common guidance is roughly one support bracket per hundred watts of panels, but actual spacing depends on engineering for local wind and snow.

Flat and low-slope roofs

• Ballasted racks sit on the membrane, usually on protective pads, and are held down by concrete blocks or the weight of the system. They avoid penetrations but add significant load and must be engineered for wind and, in seismic areas, sliding.
• Attached systems use a limited number of flashed structural anchors, reducing ballast weight.
• Hybrid systems combine some ballast with fewer attachments.
• Lightweight options include plastic wedges and tension-based racking.

Panels on flat roofs are usually tilted at a low angle; spacing between rows reduces self-shading and leaves access for maintenance.

Wind design

Wind pressures on arrays vary across the roof, with edges and corners most severe. ASCE 7-16 in the United States introduced specific methods for rooftop solar panels parallel to the roof surface. Racking manufacturers publish engineering based on these standards and on wind tunnel tests.

Roof compatibility

• Racking metals should be compatible with roofing metals to avoid galvanic corrosion.
• Penetrations through membranes must be flashed in accordance with the membrane manufacturer's details to preserve the roofing warranty.
• Ballast pads must protect the membrane from abrasion.
• Access paths and setbacks are often required for fire safety.

Removal and reinstallation

Because roof coverings may need replacing during an array's life, mounting systems that allow panels to be removed and reinstalled without damaging the roof reduce future costs.