Condensation Risk Analysis

Interstitial condensation typically occurs when warm, moist air from inside a building penetrates into the built fabric and meets a cold surface causing the air to cool, lowering its capacity to carry moisture, and resulting in condensation on the cold surface. This typically takes place in the refurbishment of existing buildings where insulation is applied to exterior walls, roof or floor construction.

In accordance with the EnerPHit standard you may need to have your construction details assessed for condensation prior to building certification. Please contact passivhaus@bre.co.uk for further information.

BRE use WUFI-2D to analyse and quantify heat and moisture through construction materials which also assess water penetration into walls/roof from the exterior surface due to rain and wind as sometimes it can lead to significant water accumulation in the construction.

  • In the calculation of heat transport, WUFI takes into account:
  • thermal conduction
  • enthalpy flows through moisture movement with phase change
  • short-wave solar radiation
  • nighttime long-wave radiation cooling

The vapor transport mechanisms included in WUFI are:

  • vapor diffusion
  • solution diffusion

The liquid transport mechanisms taken into account are:

  • capillary conduction
  • surface diffusion

 Fiqure 1: Typical WUFI output