All timber frame walls are designed to ‘breathe’. The term ‘breathe’ refers to the ability of a wall to allow water vapour to diffuse through the structure. This is an important consideration to the long term durability of the timber structure.
A breather membrane restricts the passage of liquid water, whilst allowing water vapour to pass through.
This Wood Information Sheet (WIS) covers a number of topics surrounding breather membranes including the requirements of a breather membrane, the considerations which must be made to mitigate risk of condensation, and the measures which must be taken to mitigate heat loss caused by convection currents.
Breather membranes need to combine a high degree of wet strength and water resistance with very low moisture vapour resistance.
Air infiltration through gaps in the building fabric can accelerate the rate of heat loss due to convection. An airtight breather membrane can help to mitigate this heat loss, provided laps are sealed with a propietary self-adhesive tape.