Serviceability limit state (SLS) checks verify that a structure continues to function correctly under working loads without excessive deflection, vibration, or cracking. For rooftop solar PV assessments, SLS checks are applied to purlins and rafters carrying the combined dead load of the array and any imposed maintenance loads.
Eurocode structural design requires SLS verification alongside ultimate limit state (ULS) strength checks. SLS combinations use characteristic (unfactored) loads. In practice, SLS deflection limits often govern the design of longer-span purlins under PV dead load, particularly where purlin sections are undersized relative to current Eurocode standards.