Rainbow International® of Baltimore County

Dehumidifiers are needed to properly dry most jobs. Excessive humidity in a structure is typical after water intrusion. Then, as the contractor uses rapid and massive airflow to evaporate moisture from materials, much more water vapor is added to the air. Evaporation will slow and materials will not dry quickly unless the humidity is reduced.

High humidity must not be allowed to continue, for two reasons. First, sensitive contents and materials run the risk of absorption, delamination, swelling, and so on. Second, indoor air quality is threatened by mold and other biologicals, which grow best when moisture levels are abnormally high. Microbial growth is the number one indoor air quality problem in the nation, according to a 10 year study by Healthy Buildings International (Indoor Air Review, July, 1994). And the primary cause of excessive microbial growth is abnormal moisture - excess moisture content in materials, and excess humidity in the air. Just as mold can grow in a shower stall that never dries out thoroughly, it can grow explosively after a water damage situation if the humidity is not controlled.

While the issue is complex, several criteria help determine when dehumidifiers are required.

1. Whenever the indoor humidity exceeds or will exceed 60% Rh, dehumidifiers are required for rapid drying, for mold reduction, and for indoor air quality. The Environmental Protection Agency, the Hardwood Flooring Association, and the Institute of Inspection, Cleaning and Restoration all recommend that indoor humidity should never exceed 60% Rh.
2. When porous materials like carpet and carpet cushion are wet, the most cost effective indoor humidity for drying is 40-50% Rh.
3. When structural materials like walls and floors are wet, the most effective humidity for drying is below 45% Rh, and a target of 25-45% Rh is helpful. In many cases, dry air is extremely beneficial in reducing the need for reconstruction costs, or for mold problems days or weeks after the job is apparently complete.

It is true that not every job requires dehumidifiers during water damage restoration. For example, when the outdoor humidity is below 40% and the temperature is above 60 F, dehumidifiers may not be necessary if doors and windows can be left open safely.