Water and high humidity can have many different effects on building materials and personal property, depending on the amount and length of time. Secondary damage (damage not caused by direct contact with water) is the form of damage that materials may have when exposed to high humidity levels of 60% RH and above for prolonged time periods.
There are two types of secondary humidity damage in buildings:
- Hygroscopic – This is humidity damage that occurs from materials absorbing water to the point where the material cannot continue to hold it in. Most indoor materials are designed for a normal humidity RH of 50% and below. The results range from odors, staining, buckling, deforming, delaminating and swelling of materials. The actual effects, time frame, and whether temporary or permanent is dependent upon how porous the material is.
- Fungal – bacterial odors and potential mold growth