Vapour diffusion resistance (μ) (Source: ONROM B 8110-7)
The vapour diffusion resistance figure is taken from ÍNORM EN ISO 10456 or for materials made from masonry products and mortar from ÍNORM EN 1745, whereby a unique column is added in which to record the dry and wet measurement value respectively. For some construction products not included in ÍNORM EN ISO 10456, the values for the vapour diffusion coefficients can be taken from test reports or approvals.
Masonry, wall and plastering mortar, dry build sheets:
The vapour diffusion resistance figures apply to materials used for masonry products. The dry (higher) value must be used for dehydration calculations, the wet (lower) value is to be used for diffusion into the component itself (in accordance with ÍNORM EN 1745).