Built-up roofs are one of the oldest and most prevalent commercial flat roofing systems in the UK. The multi-layer construction creates a durable waterproof membrane, but the weight of the system must be included in dead load calculations when assessing the underlying structure to carry solar PV. Older BUR systems may present substrate condition issues identified during a drone roof condition assessment.
For solar PV mounting on a BUR, structural engineers confirm that fixing penetrations through the membrane are appropriately detailed and that the underlying deck and structural members can carry the combined dead load of the membrane, insulation, PV array, and maintenance imposed load. Where penetrations are unacceptable, ballasted mounting systems may be used subject to structural confirmation.