GB 50057-2010 第5.2.9条
**** | When metal objects (such as metal railings, billboards, solar water heaters, outdoor air-conditioning units, etc.) are present on the hotel roof, their metal components shall be reliably connected to the air-termination system. If the thickness of the metal object is not less than **4mm** (steel plate) or **2.5mm** (copper plate) and it will not melt due to lightning strikes, it may be used as a natural air-termination system.