Moisture Management – Analysis

Steady-State Analysis

We study the potential for excessive moisture in several ways, always aiming to adopt a control layer approach. The steady-state method is a simple and practical method used to determine the dew point within the building envelope.

The dew point, the temperature at which airborne water vapour condenses to liquid water, is determined by both the temperature (or of the surface that is in contact with the air) and the relative humidity of the air. The dew-point temperature equals the air temperature when the relative humidity is 100%. In other words, the lower the relative humidity, the cooler the air must be to condense water saturated in that air.

As a simple approach to moisture management, a steady-state assessment is one-dimensional, considering heat flow and vapour diffusion along a straight line passing through the exterior wall.

Where saturated and actual vapour pressures meet, water vapour is deemed to condensate, and thus the dew point has been met. The results are approximations, and their validity and usefulness depend on the accuracy of the data used, including interior and exterior temperature and relative humidity, and the thermal resistance and permeance of the materials.

In climates where daily temperatures can vary significantly during a day and season, the transient analysis method is more appropriate for analysing heat, moisture, and air movement. One form of transient analysis is hygrothermal analysis.

Of course, Speckel undertakes steady-state assessments of your wall systems on the fly. Read more here:

• Wall System Tutorial 5 – Condensation Risk
  
• Speckel Wall System Condensation Calculations