COP v3.0:roofing; fastening-roofing

7.2 Fastening Roofing 

All fastenings that pierce the sheeting should be provided with adequate sealing washers to prevent leakage. Sealing washers should be made from Ethylene Propylene Diene Monomer (EPDM).

Fastenings should be tightened only enough to form a weatherproof seal without damaging the sealing washer or deforming the sheet profile. Deformed sheeting will cause water to pond around the seal.

Swarf should be removed from under the sealing washer as it will not only cause staining but also interfere with the seal.