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"Preventing Mold Growth
  in Temporary School Structures"

   March 2002
   by Bruce Stewart, CIH, ROH

Mold growth in general purpose buildings, including but not limited to schools, has emerged in the past few years as one of the most important issues confronting property managers.

Standards recently published by the New York City Department of Health and the US Environmental Protection Agency confirm that exposure to mold growth in such buildings is a risk factor for at least some occupants. Allergic responses such as asthma, hay fever, and rash may be triggered in those who have developed sensitivities to molds. A very limited number of molds may cause infections in occupants with compromised immune systems. In addition, it appears that exposures to some species of mold, capable of producing powerful chemicals known as mycotoxins, may cause a wide variety of symptoms including headache, stomachache, nosebleeds, and eye, nose and throat irritation.

One particular mold, Stachybotrys, a mold known to produce a number of powerful mycotoxins, has received a great deal of public attention. While there is considerable debate among environmental researchers as to the relative importance of the toxic versus allergic affects of this and other molds, it is clear enough that the growth of some or all molds in buildings can be harmful to at least some occupants.

The growth of mold in buildings requires the presence of organic building materials or debris that can be a nutrient base for the mold, and extended periods of high moisture. Many common building materials will support mold growth. Cellulose-containing building materials such as gypsum wallboard, ceiling tiles, jute-backed carpets, and pipe insulation are among the most commonly found supporting mould growth. However, soil and debris present in synthetic carpets, or present in crawlspaces beneath school facilities, if damp, may also be a breeding ground for mold growth.

Any source of moisture that will provide a minimum of 70% relative humidity at the surface of the material will allow germination of the spores. This mold growth can occur rapidly. The moist conditions only need remain in effect for a few days for some molds to produce spores. Witness the EPA standard that gives a grace period of only 24-48 hours in which to dry materials, after which time mold growth should be suspected.

Any school building, permanent or temporary can support mold growth, given the right materials being wetted for long enough. In fact, the diligence of maintenance may be a greater factor predicting mold growth rather than the type of building. However, for a number of reasons, some types of temporary buildings, including portable classrooms seem to have had a higher experience of mold growth. Certainly the recent Canadian experience has been that older portable designs were more prone to develop mold growth. Several local health departments have required Canadian school boards to actively inspect their portables for mold growth.

School boards in Canada and the US are responsible under federal and local regulations to provide safe environments for their staff and students. Where can building managers turn for direction on this issue? The most current advice is found in the New York City and EPA guidelines, referenced below.

Several Canadian provinces have posted either Hazard Alerts or detailed standards for employers regarding mold in workplace buildings. Particularly relevant advice is given in the 1999 Ontario Ministry of Health publication, "Boards of Health Working with School Boards and the Community to Address Concerns About Indoor Air Quality (with special reference to indoor mold contamination)." Not only does this guideline give advice on inspection, testing, and remediation of classrooms, but it also presents a number of suggestions to prevent future mold growth.

What can a school board official do to prevent mold growth in buildings?

To begin with, new temporary school facilities should be designed and built to resist water damage to the greatest extent possible. The prevention of mold growth really is a good investment for a property manager, especially in today's litigious environment.

Today, suppliers of temporary buildings have several improvements to offer school officials:

  • Cement board and non-cellulose based wall panels can be used to minimize the impact of water damage.
  • Roofs can be provided with overhangs and properly sloped eaves-troughs and downspouts to effectively manage water off the roof.
  • The siting and skirting of temporary structures is also important. The portable classroom should be placed over a well-drained surface and surface run-off should be directed away from the structure.
  • The space under the structure should be well-ventilated to prevent rot from ground moisture.
  • Diligent maintenance practices will also help prevent mold growth. Excessive use of water in cleaning of floors should be avoided.
  • Mats and trays should be provided for wet boots.
  • Maintenance personnel should carefully check caulking and flashing details around windows and service posts, especially after movement of a temporary structure.
  • Finally, classrooms should be provided with ventilation to meet current ASHRAE requirements. Although proper ventilation of a classroom will not necessarily prevent mold growth, it should reduce the frequency of general air quality complaints that are often taken as signs of mold exposure. Taken together, these precautions can go a long way to help school officials provide safe, comfortable learning environments, now and in the future.


New York City Department of Health,
"Guidelines on the Assessment and Remediation of Fungi in Indoor Environments", 2000;

US Environmental Protection Agency,
"Mold Remediation in Schools and Commercial Buildings", 2001;

Ontario Ministry of Health,
"Boards of Health Working with School Boards and the Community to Address Concerns About Indoor Air Quality (with special reference to indoor mould contamination)", 1999

US Environmental Protection Agency,
"Tools for Schools",