Light steel framing

6.10.19Breather membranes

Breather membranes shall be capable of allowing vapour to pass into the cavity, and provided to protect the sheathing and frame from external moisture.

Breather membranes should be:

  • vapour resistant to less than 0.6MNs/g (0.12 Sd) when tested in accordance with BS EN ISO 12572 using the set of conditions C and using five test specimens
  • capable of resisting water penetration in the anticipated exposure
  • „self-extinguishing
  • durable
  • installed so that each joint is protected and moisture drains outwards
  • lapped to a minimum of 100mm at horizontal joints and a minimum of 150mm at vertical joints.

Breathable membranes should be used to protect sheathing board and insulation. Breather membranes may be omitted where water resistant insulation boards with taped joints are used. Tape should be of a type recommended by the insulation manufacturer, breathable to allow water vapour to move freely and resist water penetration. Suitable taping should be applied at the lintel interfaces and other penetrations to direct water outside.