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.
Mold and mildew are fungi that grow on the surfaces of objects, within pores and in deteriorating materials. They can cause discoloration, odor problems and the degradation of building materials. They 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 ranging 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. Moreover, furnishings and grime on surfaces provide nutrients to support mold growth. Cleaning and disinfecting with non-polluting cleaners and antimicrobial agents provide protection.
Reducing Moisture
Moisture control is an important strategy for reducing mold growth. Mold growth does not require the presence of standing water; it can occur in areas with high relative humidity (RH), or when building surfaces absorb and retain moisture, allowing mold to accumulate.
Maintaining proper humidity levels is possible with energy recovery ventilators (ERV) because they precondition outside air coming into a building, precooling and dehumidifying in summer and humidifying and preheating in winter. Interest in ERV systems has increased in recent years due to lower installation costs, the Air Conditioning and Refrigeration Institute (ARI) Certification program and new building ventilation regulations.
Mold and mildew growth can be reduced where relative humidity near surfaces is maintained below the dew point. This can be accomplished by reducing the moisture content (vapor pressure) of the air, increasing air movement at the surface or increasing the air temperature.
Simply increasing surface temperatures is the best method for reducing surface temperature-dominated mold and mildew. By raising the thermostat setting or modifying air circulation, the supply air is more effective at heating the room surface.
Vapor pressure-dominated mold and mildew can be reduced by direct venting of moisture-generating appliances outside, dilution of moisture-laden indoor air with less humid outdoor air or by dehumidification.
Identifying and Correcting Mold and Mildew Problems
Exterior corners tend to be closer to the outdoor temperature because of poor air circulation, wind-washing, low insulation levels and greater surface area heat loss. As a result, 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 mold and mildew problems than buildings with less air movement. Removing obstructions to airflow will reduce mold and mildew growth.
Mold and mildew issues 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.
A mold problem can also occur within the wall cavity as outdoor air comes in contact with the cavity side of the cooled interior surface. It is a particular problem in rooms decorated with low-maintenance interior finishes, such as vinyl wallpapers, which can trap moisture between the interior finish and the gypsum board. Mold growth can be rampant when these interior finishes are coupled with cold spots and exterior moisture. Possible solutions for this problem include:
- Preventing hot, humid exterior air from contacting the cold interior finish
- Eliminating cold spots by relocating ducts and diffusers
- Ensuring that vapor barriers, facing sealants and insulation are properly installed and maintained
- Increasing the room temperature to avoid over cooling
Thermal bridges are elements 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 in building envelopes.
Windows have colder surfaces in winter, which can lead to condensation. Condensation is often controlled by using storm windows or insulated glass to raise interior surface temperatures. The advent of higher performance glazing systems has led to a greater incidence of moisture problems because buildings can operate at higher interior moisture levels without visible surface condensation on windows.
Concealed condensation often results from using thermal insulation which, while increasing surface temperatures, also decreases heat loss from the conditioned space into the wall cavity. Wall cavity temperatures are reduced, increasing the likelihood of condensation in this concealed area. Concealed condensation can be controlled in colder climates by installing exterior insulation. In warmer climates, install insulating sheathing to the interior of the wall framing, and between the wall framing and drywall.
Heating, ventilating and air conditioning (HVAC) systems
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. AAC Services is here for you and we are happy to help.
Article supplied by Consumers Energy
