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Surface and Interstitial Condensation in Insulation

Surface and Interstitial Condensation in Insulation

What are the different types of condensation, and how it relates to insulation.

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 heat is drawn out, leaving the inner surface cold.

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 can substantially reduce the performance of insulation. In order to foresee any potential condensation when installing insulation, a Condensation Risk Analysis can be performed.

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