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“There is a limited knowledge of how moisture moves in and out of solid wall construction, and in particular what happens to moisture movement when insulation is added, and natural ventilation is reduced” 

“The standards, advice and certification of internal wall insulation (IWI) for solid walls are currently wrong or misleading both in terms of moisture and heat loss. This can lead to very inefficient design and considerable mould problems” (May and Griffiths, 2015, p. 10).

The knowledge gap within the industry and the difficulty in regulating buildings of such unknown and diverse backgrounds and performances means assessment and attempting to understand how individual buildings work in their environment with people and nature are essential prior to recommending any retrofit measure as the uncertain consequences and risk must be considered as part of a wider view of building retrofit (May and Griffiths, 2015).


Traditional buildings rely on the permeability of the materials used to allow moisture to disperse via diffusion and capillary action, spreading the moisture widely and evenly to avoid any potentially damaging concentrated build ups (Historic England, 2017).

Hygroscopic, vapour permeable or breathable are terms all given to materials that are open to absorbing water (not larger air molecules) from their surroundings. This ability is advantageous as it allows the material to regulate humidity by storing excess moisture from the air to be released later when RH is reduced (Ahlberg, Georges and Norlén, 2014), thus reducing condensation and mould growth. However, this ability to buffer moisture is largely dependent on the surface finishes of plaster and paint, the exposed area, moisture quantity (Ge et al., 2014), and ventilation rate (Yang et al., 2012). Latif et al. (2015) demonstrated that a water based matt emulsion paint may reduce this ability by 62%.

Moisture in buildings