Curtain walling and cladding

6.9.9Damp proofing and vapour control

Curtain walling and cladding systems, including damp proofing materials and breather membranes, shall adequately resist the passage of water into the building and allow water vapour to pass outwards.

Damp proofing should:

  • be installed correctly to provide a physical barrier to the passage of water, and to ensure water is directed to the outside
  • include cavity trays with stop ends at the base of the system, above openings, above cavity barriers, interfaces and other interruptions to the cavity where necessary
  • use DPCs/DPMs where necessary, including the junction between the system and any other component or systems
  • use only appropriate tapes and sealant (but not solely rely on sealant) in accordance with the design and the manufacturer’s recommendations.

For curtain walling systems, the DPC/DPM should extend the full height of the system and have appropriate details at each interface (including floors, walls, roofs, balconies and terraces).

DPCs/DPMs and flexible cavity trays

Damp proofing should be:

  • formed from materials which are compatible with adjoining components
  • the correct dimensions to suit the detailed design
  • constructed from preformed components at complicated junctions.

The following materials are acceptable for use as DPCs/DPMs:

  • BS 6515 polyethylene
  • EPDM
  • Neoprene
  • Materials assessed in accordance with Technical Requirement R3.


The following materials are acceptable as flashings:

  • BS EN 12588 rolled lead sheet (minimum Code 4)
  • BS EN 485 and BS EN 573 aluminium and aluminium alloys
  • BS EN 988 zinc alloys
  • Stainless steel.

Breather membranes

Breather membranes should:

  • comply with BS 4016 (Type 1 in areas of very severe exposure), or
  • be in accordance with Technical Requirement R3.