Solar PV on a flat roof: ballast, anchoring and layout
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A flat roof can provide a useful PV site when it supports the designed loads and the installation preserves the roof layers. Panel orientation and tilt can be chosen, but row shading, roof edges, drainage and service access reduce the usable area.
Assess loads and waterproofing together
The choice between ballast and anchoring depends on the roof and project-specific wind and snow calculations. There is no universal ballast weight or panel spacing. Ballast changes roof loading; anchors require properly detailed penetrations.
Check the roof structure, covering, insulation and condition before ordering. Establish how compatible protective layers and mounting details preserve the waterproofing system.
Ask for a dimensioned layout
The design should show rows, clearances, obstructions, drains and access routes. Compare output with the actual spacing and shading rather than multiplying the entire roof area by module efficiency.
Get a written scope covering structural assessment, waterproofing responsibility, installation and maintenance access. A suitable-looking empty roof is not enough evidence for a standard package design.