There’s a lot of confusion out there about condensation, so here we explain what it is, how it relates to insulation and what controls it may help.
Condensation is the process of water vapour in the air condensing from a gas into a liquid. In buildings, it occurs when warm moisture-laden air meets with cold vapour-resistant surfaces. There are two primary types of condensation: surface condensation and interstitial condensation.
Surface Condensation
Surface condensation is condensation which occurs on the visible surfaces of a construction, rather than between the layers. Internal surface condensation can promote mould growth, thus reducing indoor air quality, as well as creating unsightly pattern staining. Thermal bridges can undermine effective insulation and can contribute to the formation of surface condensation as the cool is drawn out, leaving the inner surface warm.
Interstitial Condensation
Interstitial condensation is condensation which occurs between layers of the construction, i.e. ‘inside’ the roof, wall or floor elements. Interstitial condensation can cause deterioration or even failure of the components of the assembly, potentially shortening their useful lifespan. It is important to ensure an element is designed to avoid interstitial condensation, or to create an adequate ventilation solution to remove any condensation that forms.
Condensation Risk Analysis (CRA)
Condensation can substantially reduce the performance of insulation. In order to foresee any potential condensation when installing insulation, a Condensation Risk Analysis can be performed. Condensation risk analyses for individual elements, performed in accordance with BS 5250, are supplied alongside with U-value calculations by Kingspan Insulation’s Technical Services Department. Determining the risk of ‘interstitial’ or ‘surface’ condensation in a building depends on the components of the assembly, the order in which they appear in the construction, the building’s use and its geographical location (the calculation is based on specific local Met Office Data).