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.
Figure 1 - Moisture-Related Factors Influencing Wall Systems
| Area | Primary Consideration | Problem | Cause |
Dimensional changes |
Swelling and shrinkage as moisture enters and leaves the wood. |
||
Decay caused by condensation. |
|||
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. |
||