Mounting solar panels on an asbestos-cement slate roof

Fixings and rails

• Asbestos-cement slate: Hanger bolt M10×200 + EPDM + cap → rafters / purlins. Old slate may contain asbestos — drill wet, wearing a respirator, only on the corrugation crest, without hammer action.

Check before installation

• The age of the slate. If it was laid long ago, assume it may contain asbestos: drill with the spot wetted, wearing an FFP3 respirator.
• The condition of the sheets where the fixings go: drill only on the crest of the corrugation, without hammer action.
• Whether there is a counter-batten under the slate: it decides the hanger bolt length.

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.

In all three cities the typical roof passes with the fixing spacing the calculation chose.

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

The Solispec engine writes the steps for the typical roof in Kyiv: rafter numbers, marking out and quantities come from the same calculation. Steps that depend on the roof covering are given in full, those shared by all pitched roofs in short.

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.
2. Mark out the 11 180 × 4 720 mm array: 1 190 mm from the eaves, 410 mm from the left gable.
3. Fixings: asbestos! Respirator FFP3, keep the drilling spot wet. On rafters №2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 drill without hammer action Ø12–14 at the corrugation crest, pilot Ø7 into the rafter. Hanger bolt M10×200 (M10×250 with counter-battens), 72 pcs, ≥ 70 mm into the rafter. EPDM washer + cap + sealant, do not overtighten the sealing nut — the slate cracks. Bracket 15–20 N·m.
4. Rails: fix the rails to the brackets with T-bolt M8 (1 per fixing, 72 pcs), adjusting the bracket height so that the rails are in one plane.
5. 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.
6. 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.
7. Install the panels from bottom to top, starting from the gable.
8. 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.
9. Install snow guards above the eaves below the array across the full width of 11 180 mm, fixed into the rafters.
10. Check the penetrations after the first rain (from the attic — for any traces of water).

The shared steps in full are on the section page

Common mistakes

• Drilling with hammer action. Slate cracks; drill without hammer on the crest.
• Over-tightening the sealing nut. Too much pressure cracks the sheet just like an impact.
• Using the standard hanger bolt over a counter-batten. A longer one is needed then — the installation steps say which.