Eurocode 1 defines characteristic values and combination rules for principal actions applied to building structures. For rooftop solar PV assessment, three parts are critical: EN 1991-1-1 for dead load and imposed maintenance load, EN 1991-1-3 for snow load based on site ground snow load and roof geometry, and EN 1991-1-4 for wind actions including fundamental basic wind velocity and pressure coefficients.
UK National Annexes to each part of EN 1991 define the nationally determined parameters. For wind loads, the UK NA provides the fundamental basic wind velocity map from which site-specific design wind speeds are derived. For snow loads, the UK NA provides ground snow load maps with altitude correction. These parameters are essential inputs to accurate structural calculations for UK solar PV projects.