Light steel framed walls and floors

6.10.14Breather 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 (according to a BS 3177 test at 25°C and 75% relative humidity)
  • capable of resisting water penetration
  • self-extinguishing
  • durable
  • adequately strong when wet to resist site damage
  • 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
  • Type 1 to BS 4016 when in areas of very severe exposure.