What is a normal moisture reading for drywall?
The normal moisture reading for drywall is between 6% and 12%. Moisture readings taken in the field are typically affected by the environment (temperature and relative humidity). Environmental conditions should generally be the same from room to room at time of testing, unless otherwise noted on the report.
Building Codes and Drywall Moisture Readings
Building codes are provisions that regulate the construction of buildings and are developed to protect public safety, health, and general welfare. Local building codes often adopt model codes such as the International Building Code (IBC) and the International Residential Code (IRC). Moisture content of drywall is generally regulated by these building codes or by referencing an industry standard such as the American Society of Testing and Materials (ASTM).
For example, the IRC states that “gypsum board shall have a maximum moisture content of 15% when installed.” (2021 IRC Section R702.6.1)
Moisture Readings and Mold Growth
Mold can grow on drywall with a moisture content of 16% or higher. A moisture reading above 15% would warrant further investigation. The presence of mold can cause allergic reactions and asthma, so it’s important to keep moisture levels in your home in check. Mold growth will occur on drywall when the surface remains wet for 48 hours or longer.
How Drywall is Damaged from Moisture
- Swelling and Expansion: Moisture will cause drywall to swell and expand. As drywall expands, the paper facings can become detached from the gypsum core, causing the drywall to become soft and lose its strength.
- Buckling: When drywall absorbs moisture, it can cause the drywall to buckle and distort. Buckling can occur when there is a significant difference in moisture content between the two sides of the drywall.
- Warping: Warping is a condition where the drywall becomes twisted or bent out of shape. Warping can occur when drywall is exposed to moisture for a prolonged period of time.