Mounting solar panels on a trapezoidal sheet roof

Fixings and rails

• Trapezoidal sheet: Mini rail + 5 self-drilling screws 6.3 with EPDM → sheet (top corrugation). Steel sheet ≥ 0.5 mm. Self-drilling screws into the crest, not into the sheet overlap.

Check before installation

• The sheet thickness, from its marking or the roof documents. It decides whether mini rails can be used or the fixings must go into the purlins.
• Where the sheet overlaps run: mini rails are marked out so that no screw lands in an overlap.
• The purlin spacing under the sheet. You will need it if the sheet is too thin for mini rails and the fixings move to brackets.

Calculation for three cities

A typical 12 × 7 m slope at 30°, rafters every 600 mm, 20 panels of 2,350 × 1,100 mm in 2 rows. Snow and wind under DBN V.1.2-2:2006 for the regional centre; a 6 m high house.

Uplift and pressure are the design forces on one fixing next to the typical capacity the calculation assumes. An array near the eaves or the gable lies in the wind edge zone, where the calculation places fixings closer together.

Where the fixing fails (Kyiv, Lviv, Kharkiv), the calculation suggests placing fixings closer together or choosing a fixing with a higher datasheet capacity. The constructor shows the effect as soon as you change the spacing.

Drawings

Bill of materials for the typical roof (Kyiv)

20 panels, 11.00 kW. Quantities from the calculation for Kyiv; open the constructor for your own roof.

Installation step by step

On trapezoidal sheet the order differs from roofs with rails, so all the steps are here. The Solispec engine writes them for the typical roof in Kyiv: marking out and quantities come from the same calculation.

1. Roof inspection: from the attic, check the rafters (section ≥ 50×150 mm, no rot or cracks, spacing ~600 mm) and the condition of the roof covering. Prepare the mini rails, self-drilling screws and clamps per the bill of materials. Safety: harness with an anchor point, never work alone.
2. Mark out the 11 180 × 4 720 mm array: 1 190 mm from the eaves, 410 mm from the left gable. Mini rails: 11 per row, under every panel joint. Check: array diagonals equal within ±10 mm.
3. Fixings: along the lines under the panel joints, screw 44 mini rails onto the corrugation crest — 5 self-drilling screws 6.3×25 with EPDM washer each (220 pcs), EPDM pad under the rail. Do not fix into the sheet overlaps. Screwdriver with depth stop: washer compressed to the edge, sheet not dented. Sheet thinner than 0.5 mm — only brackets into the purlins. Check: mini rails of one row in line (string line ±2 mm).
4. Earth the array: bond the rails of each row to each other and to the rails of other rows with a 6 mm² Cu conductor via rail earthing clamps. If the rail connectors are not conductive, fit bonding jumpers at the joints. Wire — to the building's MET. Check: test the continuity of the protective conductors and the connection to the MET with an instrument (resistance — per the electrical design).
5. Make the cable penetration through the roof covering above the array: a penetration with an EPDM collar or a cable gland, sealant under the flashing. Cable — in UV-resistant corrugated conduit.
6. Install the panels from bottom to top, starting from the gable. End clamps for 35 mm frames (8 pcs) are placed ≥ 20 mm from the rail end, mid clamps (36 pcs) — with a 20 mm gap. Bolt M8×50 + hammer-head nut into the rail slot (44 pcs). Tighten to 14–16 N·m.
7. Fix the cables to the frames and rails with stainless steel clips every 300–400 mm so that they do not lie on the roof covering or rub against its edge. Earth the panel frames with earthing clips under the mid clamps or with a lug in the ⏚ hole.
8. Install snow guards above the eaves below the array across the full width of 11 180 mm, fixed into the rafters.
9. Check the penetrations after the first rain (from the attic — for any traces of water). After 2–4 weeks, re-tighten the clamps (14–16 N·m) and T-bolts (15–20 N·m). Then — inspect yearly, after hail and strong wind.

Common mistakes

• Fixing a mini rail into the sheet overlap. The calculation allows screws only into the top corrugation of a single sheet.
• Putting mini rails on a thin sheet. If the sheet is thinner than the calculation requires, fixings go into the purlins with brackets.
• Driving screws without a depth stop. The washer must be compressed to its edge and the sheet not dented.