This article elaborates on the rationale behind maintaining a 30-50% relative humidity (RH) level during water damage restoration processes, inspired by the principles outlined in both the ANSI/IICRC S500-2021 Standard for Professional Water Damage Restoration and PAS 64:2013; Mitigation and recovery of water damaged buildings. Code of practice.
Equilibrium Moisture Content (EMC) Explained:
Initially, buildings and their contents, such as floors, walls, and furniture, would have a moisture equilibrium with the air, described by the Equilibrium Moisture Content (EMC). EMC is the point at which materials do not gain or lose moisture, dictated by the surrounding air's relative humidity and temperature. Material-specific adsorption and desorption isotherms determine the precise moisture levels.
Importance of Adsorption and Desorption Isotherms:
These isotherms are crucial for understanding how various materials interact with the humidity in the surrounding air, depicting the dynamics of moisture absorption (adsorption) and release (desorption) at different humidity levels. Achieving EMC signifies a material's moisture balance with the environment, emphasising the need to restore or reduce indoor humidity to pre-damage levels for effective restoration.
Restoration Dynamics:
Materials generally release moisture more slowly than they absorb it, highlighting the necessity for extended drying periods. Reducing indoor humidity by 5 to 10% from pre-damage levels can significantly accelerate drying, which is crucial for effective restoration and damage mitigation.
Targeting a 30-50% RH for Dehumidification:
Dehumidification aims to adjust indoor humidity levels to match or be lower than before the damage, ensuring materials return to their original moisture conditions. The optimal relative humidity (%RH) varies according to external weather conditions and the temperature inside. The appropriate RH target can be found by evaluating an undamaged room of comparable temperature. In a North European setting, this leads to a desired humidity range of 30-50% RH for heated environments (20°C).
Finding the right dehumidification technology
Obtaining a relative humidity of 30-50% at 20°C will be challenging for most condensing dehumidifiers, and it only gets worse if the temperature gets lower than 20°C. Desiccant dehumidification, however, will work effectively in most conditions – one size fits all. See more here: Desiccant vs Condensation Dehumidification for Water Damage Restoration