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Controlling Mold and Mildew in Your Building

Key Points
  • Mold and mildew can cause discoloration, odor problems and the degradation of building materials.
  • Moisture control is the most important strategy for reducing the growth of mold and mildew.
  • Thermal bridges, windows and wall cavities are common areas for potential moisture problems.

ffMold and mildew can cause discoloration, odor problems and the degradation of building materials. Mold can also lead to health problems, including allergic reactions, in susceptible individuals. For mold growth to occur on surfaces, the following conditions must be present:

  • Temperatures between 40°F and 100°F
  • Mold spores
  • Nutrient base (most surfaces contain nutrients)
  • Moisture

Generally, spores are present in the air, and in most commonly used construction materials. Furnishings and grime on surfaces also provide nutrients to support mold growth. Cleaning and disinfecting with non-polluting cleaners and antimicrobial agents provide protection.

Finding and eliminating mold and mildew

Exterior corners are common locations for mold and mildew growth in winter, and in poorly insulated buildings in summer. Buildings with forced-air heating systems and ceiling fans tend to have fewer problems than buildings with less air movement. Removing obstructions to airflow will reduce growth.

Mold can be as extensive in summer as in winter. The same principles apply; either surfaces are too cold, moisture levels are too high or both. A common example of mold growth in summer occurs where cool conditioned air blows against the interior surface of an outside wall, creating a cold spot.

Mold can also occur within the wall cavity, particularly in rooms decorated with low-maintenance interior finishes, such as vinyl wallpapers, which can trap moisture between the interior finish and the wall. Mold growth can be extensive when these interior finishes are coupled with cold spots and exterior moisture.

Potential solutions for eliminating mold and mildew in these areas include:

  • Preventing hot, humid outside air from contacting the cold indoor finish
  • Eliminating cold spots by relocating ducts and diffusers
  • Ensuring vapor barriers, facing sealants and insulation are properly installed and maintained
  • Increasing the room temperature to avoid over cooling

Thermal bridges are areas of the building structure that conduct heat, causing localized cooling of surfaces. Dust particles sometimes mark the locations of thermal bridges, because dust tends to adhere to cold spots. The use of insulated sheathings significantly reduces the impact of thermal bridges.

Windows have colder surfaces in winter, which can lead to condensation. Higher-performance glazing systems increases moisture problems because buildings operate at higher interior moisture levels without visible surface condensation. Condensation is often controlled by using storm windows or insulated glass to raise indoor surface temperatures.

Controlling moisture problems

Moisture control is an important strategy for reducing mold growth. Mold growth can occur in areas with high relative humidity (RH), or when building surfaces absorb and retain moisture, allowing mold to accumulate.

Maintaining relative humidity below the dew point near surfaces will help control growth. Strategies include:

  • Reducing the moisture content of the air
  • Increasing air movement near the surface
  • Raising the air temperature

Increasing surface temperatures is the simplest method for stopping growth. By raising the thermostat setting or modifying air circulation, the supply air becomes more effective at heating room surfaces. Methods available to control moisture in the air include:

  • Direct venting of appliances and equipment
  • Ventilation to bring less humid outside air
  • Direct dehumidification

Which method is appropriate depends on the type of facility, the level of moisture problems and climate.

HVAC systems play an important role in controlling moisture and mold. Make sure your system is sized correctly for your facility and maintain a program of regularly scheduled maintenance and inspections.

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