Indoor Molds


Fate and Transport in the Environment

Methods for Monitoring in the Environment

Exposure Pathways

Methods for Measuring Human Exposure

Strategies for Preventing or Controlling Mold Exposure

Harmful Effects

Absorption, distribution, metabolism, and sites of toxicity


Molecular mechanism of action

Risk Assessment

5103/5104 Home

Strategies for Preventing or Controlling Mold Exposure

Preventing mold growth on building materials depends upon keeping water off of mold food sources like cellulose. Waterproofing and water reduction methods for roofing, siding, and foundations are crucial during construction in order to ensure a watertight building. Maintaining the water tight seal is crucial over the lifespan of the building. However, even if a watertight seal is maintained, excess moisture from other sources can also contribute to mold growth. Other sources of moisture include:

  • Condensation
  • Leaking plumbing
  • Unbalanced HVAC controls
  • Improper venting of appliances
  • Cooking and dishwashing
  • House plants and aquariums
  • Bathing and showering
Deterioration of exterior mortar
Mold and debris inside a HVAC humidification system

If excessive moisture from these sources does become a problem, it is important to keep mold growth from occurring by drying the building material within 24 to 48 hours. This time period is practical for acute events like water spills, but is impractical for more chronic problems such as condensation and HVAC problems. If chronic moisture problems occur, building materials will most likely be wet for long periods of time which will lead to mold growth. It is very important to quickly identify and correct problem areas with excessive moisture in order to minimize the chance of mold growth.

Maintaining indoor air quality is also critical to reduce mold growth and airborne mold. The American Society of Heating, Refrigeration, and Air Conditioning Engineers, Inc. (ASHRAE) 62-2001 recommends that humidity levels be maintained within the range of 30% to 60%. High humidity levels (>60%) can lead to moisture condensation and mold growth in occupied areas and inside low velocity air ducts. Filtration of indoor air using high efficiency filters will help to reduce airborne mold spore concentrations. Building indoor air quality can be improved by keeping doors and windows closed during the summer, using air conditioning to reduce humidity, and allowing the HVAC system to filter air entering the building. In areas of elevated humidity, increasing ventilation rates can help to keep condensation from occurring.

Building with drainage too close to foundation
Water staining on an air duct from a rest room plumbing leak

Abating mold sources

Mold sources may be easy or difficult to identify. Some sources can be easily observed growing on building materials while other sources can be hidden within walls, ceilings, flooring, and HVAC systems. Finding the source of hidden mold may take special instruments and sampling methods. If a mold source is discovered, several steps should be taken to prevent exposure.

Preventing exposure

Once a source has been discovered, it is critical to repair the problem that caused mold growth. If the problem is not fixed, mold growth will return on the building materials. When dealing with mold growth, it is important to keep disturbance to a minimum before isolating the area. Disturbing mold can release millions of spores into the air. People that are sensitive to mold should be relocated during mold disturbance and remediation.

The following procedures should be used to deal with the contamination that encompasses 10 square feet or more.


  • Workers should be trained on the handling of hazardous materials.
  • At a minimum, workers should use half face, negative pressure respirators with cartridges that can protect against chlorine vapors, organic vapors, and particulates (HEPA filtered).
  • Workers should wear disposable coveralls with head and shoe coverings
  • Proper gloves should be used appropriate for the material to be removed
  • The contaminated area should be isolated (air tight) from occupied spaces using plastic barriers (4-6 mil poly).
  • An exhaust fan (HEPA filtered) should ventilate the containment.
  • A decontamination room should be constructed at the entrance of the containment with a minimum of a changing area and dirty room. For large projects a 5-stage decontamination unit should be constructed.
  • Isolate the HVAC system with plastic barriers inside the containment.

Cleaning a mold contaminated area A containment to remove mold

Removal of contamination

  • Apply a 5-10% bleach solution to the area prior to removal in order to reduce the release of dust and mold spores. Wait several minutes for the solution to penetrate the building materials.
  • Porous contaminated materials that cannot be cleaned should be bagged and sealed. Before transporting out of the containment, the outside of the bag should be wiped with the bleach and water solution.
  • The hard surfaces inside the containment should be cleaned and/or HEPA vacuumed until no visible debris remains.
  • After cleaning, apply the bleach solution to the solid surfaces and keep damp for at least 30 minutes.
  • Areas that are wet should be completely dried. Apply an antimicrobial paint to the building material surfaces affected by the contamination.
  • Air and surface mold testing is optional to ensure that the area is clean.
  • Monitor the building materials to see if mold growth returns.
  • Reconstruction of the area can be performed inside the containment to contain any dust.
  • Isolation barriers and the decontamination unit can be taken down after the cleaning is complete.


University of Minnesota Facilities Management Department, Fungal Abatement Safe Operating Procedure. October 2000.

The American Society of Heating, Refrigeration, and Air Conditioning Engineers, Inc. (ASHRAE) 62-2001, Ventilation for Acceptable Indoor Air Quality, Atlanta, GA.

New York City Department of Health and Mental Hygiene, Bureau of Environmental and Occupational Disease Epidemiology. Guidelines on Assessment and Remediation of Fungi in Indoor Environments. April 2000.