Mounting systems

Step 1: identify the roof and its covering

The covering determines the fixing component, and the substructure determines whether that component can be loaded at all. Check rafter spacing, batten condition and insulation depth before ordering.

• Tile and slate pitched roofs: height-adjustable roof hooks fixed to the rafter, or to battens where the manufacturer permits it. The tile above the hook is ground or shaped so it lies flat again with no point pressure.
• Trapezoidal sheet: short rails, bridges or trapezoidal adapters fixed into the crown of the profile with self-drilling screws and EPDM sealing washers. Never fix into the trough, where water stands.
• Folded sheet metal: standing seam clamps grip the seam and require no hole in the roof. Clamp choice depends on the seam profile, single fold, double fold or snap seam.
• Shingle, cardboard and bitumen roofs: hanger bolts or double-threaded studs through the boarding into the rafter, sealed with EPDM and a flashing collar or a welded patch in the membrane.
• Flat roofs: ballasted trays and frames on protection mats, or penetrating supports where the roof structure and the membrane detail allow it.

Step 2: flat roofs, ballasted or penetrating

On a flat roof the governing load is wind uplift, not weight. A ballasted load system resists uplift with concrete blocks, paving slabs or gravel trays, so nothing pierces the waterproofing. It is the default on membranes still under warranty, but it adds mass, often 40 to 120 kg per module depending on zone and tilt, and the roof has to be able to take it.

• Ballasted, east and west facing: a back-to-back layout at roughly 10 to 15 degrees. Low profile, low wind attack area, less ballast, more kWp per square metre, flatter daily production curve.
• Ballasted, south facing: rows at roughly 15 to 20 degrees with row spacing to avoid mutual shading. Higher peak yield per module, more ballast and more roof area per kWp.
• Penetrating supports: the only option when the structure cannot take the extra mass. Every support needs a sealed sleeve or a welded flashing detail executed by a roofer, and the roof warranty has to be agreed in advance.
• Aerodynamic deflectors and wind protection: reduce uplift and therefore ballast, but they only work with the exact system components the calculation assumes.

Step 3: wind load, snow load and the static calculation

Loads come from EN 1991-1-4 for wind and EN 1991-1-3 for snow, applied through the national annex. The inputs are wind and snow zone, terrain category, building height, roof pitch and the position of the array on the roof. The output is either a maximum spacing between fixing points or a ballast mass per position.

• Zones matter more than averages: corners and edges of a roof see far higher suction than the interior. Arrays are usually kept a defined distance back from the roof edge for exactly this reason.
• Rail span: the profile height and the load together set the maximum distance between roof hooks, typically in the region of 1.2 to 1.7 m. Heavier snow zones mean more hooks, not a longer rail.
• Existing structure: a mounting calculation proves the system, not the building. On older roofs, commercial halls and any penetrating flat roof solution, a structural engineer should confirm the roof can take the added load.
• Documentation: keep the configurator output with the handover file. It is the evidence that spacing and ballast were designed rather than estimated.

Step 4: rails, clamps and earthing

Rail profiles come in several heights. A taller profile spans further with fewer supports, which is usually cheaper than adding fixing points on a difficult roof. Clamps must match the module frame height, commonly 30, 35 or 40 mm.

• Mid and end clamps: mid clamps hold two adjacent modules, end clamps close the row. Both must sit inside the clamping zone the module manufacturer marks in the installation manual, otherwise the module warranty is void.
• Torque: tighten to the value in the system manual, not by feel. Undertightened clamps let modules creep, overtightened clamps deform the frame.
• Rail splices: connectors extend a rail but have their own span rules, and a splice should never sit directly over a support unless the manufacturer says so.
• Bonding and lightning protection: rails and frames are bonded into the equipotential system, and separation distances to any external lightning protection have to be kept.

Step 5: aluminium, stainless steel and galvanic separation

Aluminium profiles with A2 (1.4301) stainless fasteners are the standard pairing and behave well inland. Choose A4 (1.4401 or 316) stainless near the coast, on industrial sites and in swimming pool or agricultural atmospheres where chlorides and ammonia attack A2. Corrosion problems almost always come from a third metal or from contamination.

• Keep copper and lead away from aluminium: the potential difference is large, and runoff from a copper flashing onto an aluminium rail is enough to start pitting. Separate with EPDM pads or route the water elsewhere.
• Galvanised and Aluzinc sheet: use the fixings and sealing washers the roof sheet manufacturer allows, and avoid dragging bare aluminium across a coated surface.
• Fresh concrete and mortar: alkaline attack corrodes bare aluminium, so ballast blocks and foundations need a separating layer or a coated contact face.
• Do not cut aluminium with tools used on steel: embedded ferrous particles rust and stain the profile. Deburr and protect every cut end.

Step 6: carports, ground and balcony structures

A solar carport is a load-bearing building, not a roof accessory. It needs foundations sized for the ground conditions, either concrete pads or ground screws, clear headroom for vehicles, and a decision on whether the roof must be watertight, which calls for module clamping into drainage channels rather than open clamps. Carports pair naturally with a wallbox, so plan the cable route before the columns are set. Balcony structures are far smaller but still see full wind load, so the bracket must suit the railing type and every fixing needs a secondary securing against the panel dropping.

Quick comparison of roof types and fixings

Swipe the table to the left