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Moisture and Wall Systems

Moisture and Wood

Problem: Decay Caused By Condensation.

Cause: Fungal growth (Figure 1) in the cell walls of wood.

Fungal growth will occur when moisture is present between the temperatures of 68° and 86°F (20° and 30°C).


  • Provide a moisture-free environment.
  • Since you can exert little control over the temperature and supply air in cavities, the best way to prevent decay is to provide a moisture-free environment for it. Most fungi cannot reproduce when moisture content of wood is less than 19%.
Fungal Decay In Window Frame
Figure 1 - Fungal Decay In Window Frame