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Moisture and Wall Systems


Directly or indirectly, moisture is the single greatest source of construction defects in wall systems. These defects can be the result of:

  • changing moisture levels in framing materials,
  • the movement of vapor-laden house air through the envelope,
  • The movement of external moisture into the building cladding systems.

These factors might cause structural failure, the deterioration and decay of wall assembly components, visual and aesthetic problems and poor performance of the building's thermal envelope as shown in Figure 1.

Moisture-Related Factors Influencing Wall Systems
Figure 1 - Moisture-Related Factors Influencing Wall Systems


Table 1 - Moisture-Related Factors Influencing Wall Systems
Area Primary Consideration Problem Cause

Moisture and Wall Systems

Moisture and Wood

Dimensional changes

Swelling and shrinkage as moisture enters and leaves the wood.

Decay caused by condensation.

Fungal growth in the cell walls of wood

Moisture and Air Leakage

The movement of ward, vapor-laden air through the wall system in winter.

Pressure differences between the interior and exterior of the building

External Moisture

Rain an snow penetration into building cladding systems.