COP v3.0:external-moisture; sealing-washers

6.3 Sealing Washers 

All fixings that pierce the sheeting should be provided with adequate sealing washers to prevent leakage.

Fixings should be tightened only enough to form a weatherproof seal without damaging the sealing washer, or deforming the sheet profile.

Positive sealing is necessary with to prevent leakage with pan or valley fixings. The fixings should not obstruct the free flow of water and should not be over-tightened. Over-tightening may cause rotation of the washer while driving, and can cause inadequate sealing.

Over tightening nails or fasteners can damage the washers or deform the roof profile and water will 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.

Sealing washers should be made from:

  • Ethylene Propylene Diene Monomer (EPDM).
  • Neoprene, containing no more than 15% carbon black filler by volume or 25% by weight.
  • Closed Cell PVC foam or another UV resistant, resilient material that will perform its function for at least 15 years, and is compatible with the roofing material. Some foam washers do not remain flexible for this long and may jeopardize the sealing capacity of the washer.