Remember that when moisture is present mold and dangerous bacteria start to grow in just a few days. One to 2 days for mold and 3 to 5 days for bacteria inside your home which can degrade into what is called category 3 water (or black water) due to abundant bacteria growth in as little as 2 days after the 3 to 5 day initial bacteria growth starts. This is the same category of water you flush down your toilet! This is a severe health hazard which is why you would want to address any signs of moisture quickly.
Industry guidelines normally use 18% moisture as a threshold for moisture being present in drywall. However, even 17% measured in drywall can cause the integrity of the drywall to degrade and become soft over a relatively short period of time. Typically, when I find 17% moisture in drywall at the top of the baseboard that usually means the reading is higher at the very bottom of the drywall that is behind the baseboard trim.
Drywall moisture is mentioned here because drywall is ‘food’ for mold growth where other materials are not as much. So, whether you purchase a moisture meter yourself and measure moisture (you need to learn how to use them and interpret the readings) any moisture reading in drywall at 17% or higher is not good. Usually, when there is an active leak or some type of water intrusion the moisture found will be much higher and you want to address the situation promptly to safeguard your health and that of your family.
Steve Mullins (i.e. Mold Detector)
CMC, Certified Microbial Consultant
Moisture and Mold Detection, Inc.